Episode 235 - Aquatic Plants

You're listening to the Common Descent Podcast. Hello, Will. Hello, David. Hello, listeners, and welcome to Common Descent, a podcast about paleontology, evolution, and the history of life on Earth. This is episode 235. Long-time listeners know what that means. Plants time. This episode, our topic is aquatic plants. Plants that are specially adapted for life aquatic. And as usual, since neither Will nor I know anything about plants, we will be joined for this discussion by our favorite guest of the podcast, Dr. Allie Baumgartner, plant expert extraordinaire, who will talk to us about what makes a plant aquatic, what adaptations allow plants to be aquatic, and what we know about the deep history and evolution of aquatic plants. Yeah. I feel like this is one of those categories people might not consider because, like, animals that go back to water get fins and flippers and very clearly, but many water plants to us layman's just look like more plants. Just more plants. That's just plants, but what? Yeah, I had never put much thought to how tough must it be to not grow in dirt or at least grow in dry dirt. Well, you know who put more thought into it than we did? All the people who requested this topic for us to talk about. This, we had to do this episode because the list of requesters was racking up. This topic was requested by Josiah, Eliza, Lydia, Athena, Luke, Gazeboist, Allison, Varun, Leaf Build Species, Tony, Azola Event, Lori, Noah, Amber, Mercedes, Ryan, Nina, Tara, Emmett, Chris, Richard, Amanda, Echevarria, Cinder, and Jackie. Woo! Good requesting, everyone. Thank you all for your request. Clearly, we don't talk enough about plants on the Common Descent podcast for all these requesters. Fortunately, there's a whole other podcast out there called Leaf It to Us, where friends of part of the podcast family, Nora and Allie, Dr. Allie Baumgartner, paleobotanist extraordinaire, talk all about plants. Season one of Leaf It to Us came out last year, 2025, 12 episodes, plus some bonus content. And season two is in the works as we speak. So if you can't get enough of plants or you can't get enough of Allie, go check out Leave It to Us for all of your plant needs. Yes. Before we move on, some announcements. As usual, we have an incredible community of listeners who not only submit requests for cool topics for us to talk about, but many of whom also support us on Patreon. The support we've received from Patreon allows us to do everything we do with the podcast This podcast is possible thanks to that support In exchange, patrons get access to bonus content Just the other day, we recorded the first bonus news and bonus noise of 2026 We do live streams, all sorts of cool stuff And at certain levels, patrons get their names shouted out here on the podcast when they join this episode we would like to welcome our newest patrons, Alessandra and Lucky Otter. Welcome, welcome. Thank you for joining and supporting us. Thank you so much to all of our patrons, past, present, and future. That could mean you. If you're interested in supporting us on Patreon and checking out our bonus content, go down to the episode description. There's a link in there. Or go to our website. Or basically anywhere you find us, somewhere we've snuck in a link that you can follow to the Patreon. Because it's that important. Anywhere Common Ascent products can be found. And speaking of ways to support us, every now and then people send us mail, like physical packages, which is a very old-fashioned thing to do. We got some mail from Elizabeth that includes some agates from Lake Superior, which are very pretty. They're shiny and all smooth. And then some neat stickers from state parks in Minnesota. We got temperance and Tedaguch State Park. Thank you, Elizabeth. Very thoughtful. When people send us, in addition to it just being like, oh, cool, a nice present, the mail we get is always from very thoughtful people. Yeah. And Elizabeth mentioned that the agates had been waiting to be sent, or the agates and stickers have been waiting to be sent. So, like, they had these in mind for us for a while. And that's very sweet. So it's just, yeah, thank you, thank you, everyone, when you send us neat stuff. It's a new year here in Common Descent land and also in, you know, the world. And we've got a couple of cool things coming up. For one thing, shortly after this episode comes out, the podcast is turning nine. We will be celebrating nine years of Common Dissent with an anniversary livestream public, not just for patrons. Anybody can join. It'll be on YouTube on Wednesday, January 28th, which is the ninth birthday of Common Dissent at 7 p.m. U.S. Eastern Time. Come to the livestream. We will do some chit-chat. We'll have Q&A with our audience, and we'll make some special announcements about things that are coming up later in the year. Yeah, it's going to be good. Show up. Shortly after that, we start releasing our first special series of the year. Poke-E is coming out in February, a spinoff of Spooky. Spooky is where we speculatively evolve monsters from popular fiction. Poke-E is a special series for February where we will be speculatively evolving Pokemon. I'm so very excited to see what people make of our creations. There will be five episodes starting to release the first weekend in February, and then every Saturday from there on right until the beginning of March, every episode our speculative evolution will be focused on legendary Pokemon in honor of the 30-year anniversary of the Pokemon franchise, which has brought us so much joy, and through this podcast, money. It's financial support. Speaking of special series, back for 2026 is Bricks with Basque. Yeah! We had so much fun doing it last year. I say we, I didn't do anything. Will does Bricks with Basque, where Will makes Lego builds based on topics we've discussed on the podcast. It was so much fun in 2025 that we thought that Will would do some more of it. Yeah, there'll be some 2026 updates that we'll discuss on our anniversary live stream, so check in then for all the details, but more Legos on the way. Very cool. You can find that on ConfidenceN YouTube channel, and you can find the builds for these Lego creations on that Lego site that I don't remember the name of it. Re-brickable. All of the designs that have been in the episodes are up there with instructions and parts lists. So if you're interested in building these, you can find all of that available there. And you can order the parts on various other sites. You can build your own Therizinosaur or your own other stuff that you've built. Owlbear. Yeah, everything from Therizinosaur to Owlbears to Godzilla. And that was the third one. Right. Listen, there is no end to the number of marine reptiles that you can build out of Legos. I can't escape. Well, those are some announcements. Before we transition over to talking about our main topic, we have to go over some news. In fact, this is our first news of the new year. Well, I guess that's not entirely true, but these news items are from the new year. Whereas in the last episode, I'm pretty sure all the news items were technically from 2025. But there's a lot of news, even though we have just begun the year. New stuff going on in the world of paleontology evolution-related sciences. Will you go first? Happily, my first news is about the age of fishes, you know, the famous boom in fish diversity in the fossil record, and that it may have been triggered by the mass extinctions in the late Ordovician. This is researched by Wahe Hagiwara and Lauren Sellin in Science Advances, and the article is a press release in phys.org. When we look at the fossil record, many and most of the vertebrate lineages, which are going to be your early fishes, are first really recorded in the mid-Paleozoic, which is well after the Cambrian, where many of their lineages got their earliest starts, and the Ordovician, where we see a bunch of biodiversification. So there's this gap between when the ancestors of these lineages should have first appeared or been evolving, and when we really see their fossil record appear. Right. These early fish were around for a while, but they didn't really explode in diversity until the Devonian period. Yes. This gap has often been attributed to either sampling issues, you know, that we're just missing those fossils. We don't have the fossils that would show us the diversity that would have been there or that there are lineages that have just hid away somehow, missed the fossil record or are very, very rare and would be showing this. They wanted to look into this gap and the dynamics. So they looked at some more recent data on fossil deposits of the Paleozoic that covers 200 million years of the late Ordovician and early Silurian to try and reconstruct the ecosystems of those times. integrating fossil record, but also biogeography and morphology and ecology to try to get a overall look at who's in the environments, what are the environments looking like, what's the dynamic. And they found an interesting pattern related to the late Ordovician mass extinctions. So toward the end of the Ordovician, there were mass extinctions that came in two major pulses. One, because of a bunch of freezing that happened on Gondwana, which was the massive southern supercontinent. This freezing dried up a bunch of shallow oceans and changed the ecosystem, cooling things down. As things began to recover from that, a few million years later, it began to warm back up, and those who had started to adapt to the cold now had to deal with a bunch of warming water. Yes. And this one, two killed like 85% of marine species. Massive amount of life on Earth. Details about that in episode 85 of this podcast. Based off of their research, it seems that this event may have been the triggering catalyst for the diversification of early fish and caused the sudden rise in fish. Interesting. They noted parallel radiations of jawed and related jawless fish, seeing things like jawed fish becoming dominant after this event and associating it with, you know, obvious things like the loss of previously more dominant groups, which often happens after mass extinctions. But also they noted some interesting ecological dynamics that most of the vertebrate survivors were confined to refugia, which we've mentioned at times before, are these areas of protected ecosystems, usually small, isolated areas, basins when it comes to the ocean. And on Earth, these could be valleys or even like mountaintops, places that can kind of hide away from changes happening elsewhere and act as a safe pocket for survival. It seems that bees acted as little biodiversity hotspots. And the surviving fish were able to then come out of the refugia and have an advantage in this post-extinction world. Interesting. The researchers said that from their data, the extinction led directly to a gradual but dramatic increase in fish diversity, gnaxostome, jawed fish, and jawless fish biodiversity, with a gap of like several million years from the extinction to us seeing this event, this biodiversity increase, and that they seem to have been concentrated in these refugia for millions of years until they somehow evolved the ability to leave them or something changed enough for them to be able to leave them and spread out. And that it seems that they then stepped into the niches and ecological roles left open by the previous victims of the mass extinction. And they noted that the pattern they saw with this specific event also matches those from other climactically similar events, things like the endovonian mass extinctions, and that those also had a post-extinction gap, like we see here, of low biodiversity that then was filled in by the survivors, and that they are calling this a diversity reset cycle. Yeah. That there seems to be a fairly similar pattern in these kinds of events of that gap, and then members filling back in the roles that were left vacant. It's a really intuitive explanation of what happens after an extinction. And we've talked about this before, that you have an extinction, and then after a mass extinction event, you have a changeover, right? The famous example being the end Cretaceous, dinosaurs largely go extinct, and then the Cenozoic is the age of mountains, because you lost that previously successful group, and now a new group comes in. But even though that is something we recognize happens on a broad scale, having details from the fossil record to help us understand how those survivors made it through and came to rise again, and on what time scale, in this case that these were certain groups of fish that survived in pockets. And then after some recovery period, they were able to come back out. And now you have fish, you know, because that those early parts of the Paleozoic, the Cambrian and Ordovician, there are fish, but they're not particularly a big deal in the ocean ecosystems as we think of them today. Then in the Silurian, after that extinction event, you see this rise in diversity of John Fishes. And then in the Devonian, famously, you get this wild diversification of them. Yes. So it's one of the first times where we've been able to actually get some data on why these groups might have been the ones to step back in. They seem to have been in the right, the survivable areas that they were in these refugia that then let them weather the storm of the mass extinction and eventually come back out. Now, why they stayed in the refugia and why they were able to eventually leave is not, you know, we don't have answers as to why exactly they ended up in those refugia and what eventually led them to spreading outside of them. That is information we can look into in future studies. But it's pretty cool that we have maybe a further look into this dynamic as a whole and specifically what happened with Fish. Yeah, well, and it's also a fun reminder that every mass extinction changes the world. Yes. You know, we tend to focus on the big two, the Permian and the Cretaceous, because they mark the end of the literal end of an era. The end of the Paleozoic and the end of the Mesozoic. And they both started and ended the age of reptiles. But the Ordovician Extinction and the Devonian Extinctions and the Triassic Extinction, even though they don't have quite as influential a place on the timescale, the world was still a different place before and afterwards. And so understanding the dynamics of what was different. And in this case, one of the big differences was fish. Fish became fish as we start to know them. Very cool. Well, as it happens, I also brought along some news about marine life in the aftermath of a mass extinction event. Nice. In this case, particularly ammonites, the famous coil-shelled, squid-faced marine creatures of the Mesozoic era, and an investigation into ammonites after the end Cretaceous mass extinction event. Cool. This is research published in Scientific Reports by Marcin Mikalski et al. And we'll link in the blog post. We'll put a link to a press release from phys.org attributed to Paul Arnold. Ammonite, if you are a fossil headed person, you've probably seen ammonites before. They look like modern nautiluses. They've got a squid face. They're cephalopods, relatives of octopus and squid. but particularly a group that is uniquely diverse in the Mesozoic era, the age of reptiles. They also are famous victims of the end Cretaceous mass extinction. When you look at the list, you know, who went extinct at the end of the age of dinosaurs? It was dinosaurs and pterosaurs and mosasaurs. But if you scroll down the list a little bit from, you know, the big famous stuff, Ammonites are one of possibly the most famous invertebrate casualties of the end Cretaceous mass extinction. Yeah, because they're one of the most charismatic fossils out there. It's them and trilobites as, like, the champs of invert fossil record. Oh, and, like, if you quickly need to let people know you're talking about fossils, you know, put an image of an ammonite. It's why video games so often. Yep, the little coiled shell. It's so iconic. So ammonites are restricted to the Mesozoic era because they go extinct at the very end of the Mesozoic, or so we believe. There have been over the years some examples of ammonite fossils that appear to be younger than the Cretaceous, which would suggest that they are survivors, right, lingering members of the group that survived after the extinction. There have been some suggested cases in New Jersey, in the Netherlands, and in Denmark, but they've been disputed, right? Because in some scenarios, it can be easy to either make a mistake about what layer you're in or for fossils to get shifted over time and moved out of their original layer into a new layer or reburied. So there's been a lot of question about, like, okay, are these actually survivors or are these just fossils in the wrong place? Yeah, when you first said that's what the news is about, I didn't process exactly what you said until I'm only and went, wait, what? Yep, yep. Yeah, this is the ocean invertebrate equivalent of finding T-Rex in the paleogene. Yep, yep. Right, where it doesn't belong. So this research is basically doing a re-evaluation of ammonite fossils from Denmark, from a locality called Stevens-Klint, which is a coastal cliff that you get. There's a number of these famous kinds of localities, especially over in Europe, where you have these cliff faces that preserve chunks of the geologic past. In this case, this is a cliff that is famous because the KPG boundary is preserved in the cliff. So you can see the end of the Cretaceous within these layers, which means that you have the layers just before that in the latest Cretaceous and the layers just after that in the earliest Paleogene. Stevens-Klint is actually a UNESCO World Heritage Site in part because of this incredible geologic resource. Here at this site, there are ammonites that were identified back in the 1990s in the early Paleogene limestone after the extinction boundary. There's been dispute about them. They have been considered most likely that they got shifted out of the lower layers. They were Cretaceous, and then they got moved by some geologic process and shifted up into the Paleogene layers where they didn't originally belong. This research is taking a closer look. They examined 10 ammonites that were excavated in 2009 and 2013, so relatively recent excavations, that were found in these earliest paleogene, post-extinction layers. All of these are shell molds, so either the internal or external mold of the shell. And the researchers note several features that seem to contradict the idea that these were reworked or moved fossils. For one, they note major differences in the species of ammonites that are identified before and after the extinction boundary. These after ammonites don't show evidence of, like, damage on the surface or remineralization, the kind of things that might happen if they got moved or reburied. They note that the ammonites aren't alongside other Cretaceous fossils, even some of the really durable ones. Like, if you would expect any of them to get moved, it would be these really durable fossils. And it only seems to be these ammonites. And the ammonite, the material, the sediment inside of them is filled with bits of sponge, right, fossil sponges, that are common in the paleogene sediments, not in the Cretaceous sediment. In fact, one of the 10 ammonites they looked at was found buried in a pile of Cretaceous fossil bits. And so they went, that one looks like it was shifted out of the Cretaceous. Like, it's a chunk of Cretaceous layer that got moved, and it's still surrounded by these Cretaceous microfossils. But the other nine don't show that pattern and don't seem to have shifted out of the Cretaceous layers. which suggests that they found at least nine ammonite fossils that are paleogene ammonites, post-extinction ammonites. Cool. What's more, they identified at least three genera. This wasn't like a species that eeked across the boundary. They identified Hoploscapites, Baculites, and Fresvillia, which I believe are also different families of ammonites. So a diverse assemblage of these ammonites. Now, if these are, in fact, early Stenozoic ammonites, which is wild, exactly how they survived is unclear. It's possible that this area was one of those refugia, right? It was a place that, for whatever reason, the conditions allowed some ammonites to survive. Also, how long they survived is not clear. the researchers note that in this cliff locality, these amoni fossils have only been reported from the very oldest part of these paleogene layers. So it seems that they probably lasted, you know, thousands or tens of thousands of years, as opposed to millions of years, right? They didn't actually make it all the way through the Paleocene. They are just present at the very beginning. And then the last open question is why they did eventually go extinct in this area. Also, we're not sure. But it seems that some populations of Ammonites possibly did survive in a region, but didn't survive well enough to then re-diversify and take over again. They were still on the way out. They were still a relict community. Yeah, which is, first off, very cool way to approach it of if this is indeed that they've been shifted, what would we expect to see? And do we see that? Yeah, I love it feels like a scene out of a legal drama that you're like, cool. Among our 10, here is an example that shows exactly what we would expect to see. Yep. The others don't. Yep, it's very cool. Yes. Well, and also, like, noting that these are not the species that we do see that would have been the ones we'd expect to be shifted. So it would be very weird if the only ones shifted were only species that also did not preserve in. It's just a very logical breakdown of it sure does seem like it makes more sense that they actually lived here. Yeah. And it's a really good point to make that, like, they weren't surviving a huge long time after the mass extinction. They hung on for a little bit. Because we see this happen, like the first thing that came to my mind was like the Tuitara, where we have a little island population that it is quite potentially likely that millennia and millennia from now, people might not be able to find that fossil record of that small population. And they'll be like, oh, yeah, they went extinct this far ago. Right. We know that they lasted much longer than that, but not widely, not diversely, not super successfully, just technically. And that happens. Yeah, these ammonites weren't getting eaten by whales. They were really just at the very beginning of the Sinozoic. And I'm sure that this information will continue to be disputed because, frankly, this is a big claim. Yes. Right? That's a big deal, if that's true. It's not a huge game changer, but it is a significant piece of information we didn't have before. So I'm sure there'll be continued disputes. I'm sure that other researchers will come in and want to do a double, triple check. But if this holds up to scrutiny, not only does it mean that Ammonites survived past the Cretaceous, at least for a little bit, in Denmark, but it means that those other areas where this has been suggested to have happened, it makes that much more likely. that those could be true. So now we have to go back to New Jersey and we have to go back to the Netherlands and look at those examples. Were there multiple refugia around the world? And if Ammonites were eking through the extinction event, are there other things, right? Was there a refugium of tiny mosasaurs somewhere that just survived a few thousand extra years? Yep, yep. Well, it's because we get this question of, like, could, how likely is it that this group might have survived a little bit past? And it's very likely that a group did, you know, that a species somewhere hung on for a little bit longer, just that not widely enough or maybe in a place that doesn't fossilize well. So we have not gotten a glimpse of this exception that proves the rule of, they still functionally went extinct, but not technical. And that's really the important point about this is the functional extinction. These ammonites, if they did survive, almost certainly were a negligible impact on early Cenozoic ecosystems. Yes. Right. They weren't around making big changes. They were lingering and then they disappeared finally. Yes, exactly. This is one of those we're splitting hairs in our definitions of what counts as fully extinct. but functionally things have not actually shifted much. Yes. Very cool. My next news is modern, but it is something interesting, something we don't talk about very often. It's about our gut microbiome. Ooh, we don't listen. If plants are something we rarely ever talk about on the podcast, microbes are really, they really get the short end of the short straw here on the podcast. Absolutely. This news is about how our gut microbiome evolves. Ooh. Yeah. Our own little internal ecosystem. Yes. This is research by Richard Wolff and Nandita Garud in Nature. And the article is by Dr. Priam Bose in News Medical Life Sciences. So our gut microbiome are the many, many different microbes, many bacteria, but also viruses and other things that are inside our digestive tract and are a big part of our digestive process. These are helping us break down different foods and chemicals and minerals to make some of them usable, to make some of them accessible and are key to the way we survive. This is the thing that lets cows and other plant eaters digest plant material. They have special microbes for that. Also allows us to digest plant material. Yep, yep. And we have a bunch of different species all in there helping out with different jobs. Some not helping out. Some just living inside us. But many, many of these organisms are important to our survival and a key aspect of how we function. And since they are little living organisms, they do evolve themselves separately from us, or at least in their own way. You know, our DNA is not affecting their DNA. Yeah, in the same way that, like, our parasites evolve separately, separately but related to us. Yes, they are evolving through a bunch of different means of adapting to the foods we're eating, adapting to, you know, chemicals that might enter our system, and they can adapt quite rapidly. Much of this adaptation is through horizontal gene transfer of sharing genetics between bacteria, both of the same species and of different species. Wild microbe stuff. Yep. This is allowing them to share that this microbe adapted to antibiotics. And so it's going to share that with another or to process some new nutrient. And it's going to share that with the others. This study was wanting to look at how much of this gene transfer and this adaptation and evolution of our microbes inside us was selective, was for survival and adaptation, not just random changes happening and random new genes developing. They developed a new technique for scanning the genetics and this pattern of transfer that they named Integrated Linkage Disequilibrium Scores, which is going to identify adaptive genes, alleles, spreading across the microbes so that they can see the pattern of these genes and how they move and when they're being spread. Yeah, this comes up a bunch in evolutionary genetic studies where there are certain patterns of gene spread that reflect selective pressure. Yes. This is this is a gene that improves survival. So it's going to spread more rapidly rather than just a random pattern of this happened to get passed along here and there. Exactly. Part of how they are able to track these things is that when horizontal gene transfer happens and when this spreading happens, when the adaptive gene, you know, the useful gene gets carried over, it sometimes can carry with it random, you know, neutral and sometimes maybe negative genes that were attached to its sides or whatnot or within the code. So you get these hitchhikers along with the gene being actively shared and looking for these patterns of hitchhikers and adaptive genes is helping them to track the movement of these genes across a microbiome. Cool. And so you can find these combinations of genes across different individuals to represent that they were shared. They used simulations to test how positive selection and hitchhikers would raise what they call linkage disequilibrium, which is the pattern that you see when you get this elevated sharing of DNA, and whether the pattern is unique to selection or occurs at random. And they found that the genetic pattern that they see with this does not arise without positive selective force. Interesting. That was under various evolutionary scenarios. So it seems like this spreading does not happen if there isn't some benefit. They measured then this pattern, looking for this pattern in human gut bacteria to see if it actually occurs in natural populations. They analyzed the metagenoic data of 693 people across three continents, looking at a total of 3,316 haplitites from 332 species. I love listing the numbers for genetic studies because it's always just hilarious and wonderful. And you just had gut stuff from 700 people. Yep. They identified 155 sweeps of that spreading of a gene affecting 447 different genes. Some genes were like in classes that were repeatedly under these selections and sharing. Some of these being things for like starch utilization and targeting other specific nutrients. So they did find that it seems that this does indeed happen with the similar patterns they modeled. One example was they found notable focus on genes specialized for carbohydrate metabolism, which does indicate an adaptation to host diet, that it seems like they are adapting to our intake of carbohydrates, and that they found these targets differ significantly between populations in more industrialized and less industrialized populations. That makes sense. You see a lot of dietary differences. Yep. In those different communities. And that it seems that our microbiome is adapting to those different diets and that we can see it in these patterns. that's super cool because it's one it's another one of those things that like i i would have guessed that that was happening yep but until we actually look at it and see how is it happening is it happening on what scale is it happening but also that each of our bodies has a little ecosystem inside of it and it evolves that like your internal ecosystem is evolving on a different trajectory than my internal ecosystem. And it might be because you ate more chicken than I did. Yep. Or whatever. Right. That like you drink milk more than I do. And so your internal ecosystem is like, all right, we got to be ready. Be ready for milk. Yep. Absolutely. One specific example they gave was one of the sweeps was at a locus for metabolizing maltodextrin, which is a synthetic starch that has become more widespread in industrialized diets. So they were able to say like, yeah, this ingredient we found sweeps specialized for digesting it specifically. So even very specific ingredients, we can actually identify that in the pattern. This makes me, the first research that this makes me want to do is you see those news stories every now and then of this like this man has eaten mcdonald's every day for seven years what is that guy's microbiome look like yeah yep yep those were like uh people who fast you know who go on these like long fasts find find people in those extremes of dietary habits like what does that person's microbiome look like oh very interesting when you appreciate that Like you said, you have your own little community that is specialized, that has evolved to your diet. It really does then make so much more sense when you have things like someone goes to another country, you know, visits another country on vacation, eats the food there. That's perfectly normal food there. But then they have a horrible time with it. It's like, well, yeah, because you have not adapted your microbiome to that venue. You spent 10 years training your microbiome to handle hamburgers and french fries Yeah And then you went to Thailand Yes exactly And you ate something completely different and now your body doesn know what to do with it And so it makes so much sense once you realize that, yeah, your body actually does process it differently. It's not just your preference or your open-mindedness or lack thereof. It is, my stomach literally doesn't quite know what to do with this fully because it hasn't seen a lot of these things and it's not ready for them. Yes. Yeah, my stomach is not vaccinated against this culture's food. Yes, which is, it's cool. Well, I've got one last bit of news for this episode and bringing it back to our roots, this is about dinosaurs. Specifically, this is about a hidden diversity of dinosaurs in late Cretaceous Europe. Secret dinosaurs. Secret, and these are secret dinosaurs. This is research published in Nature by Susanna Maidment et al., and we will link in the blog post to an article on Discover Magazine written by Anastasia Scott. In Europe, during the late Cretaceous, right before that extinction event that we were just talking about before, Europe was along the edge of the Tethys Sea, episode 171. So Europe was mostly a bunch of islands. It was an archipelago of these islands. And so you get these sort of unusual communities where you have island populations. You have a bunch of species with restricted ranges. You have distinctive groups such as the rhabdodontids. Rhabdodontids are this group of kind of mysterious dinosaurs that are generally considered an early branch of Iguanodontians. So in the realm of your hadrosaur, duckbill-style dinosaurs. But we also don't know very much about them because mostly they're incomplete remains. They're very abundant, but we just don't have a lot of really good skeletons. So you have distinctive groups, and you also have missing groups. Very notably, Late Cretaceous Europe has no horned dinosaurs. Weird. The Triceratops group, they're extremely abundant in North America in the Late Cretaceous and extremely abundant in Asia, but no definitive horned dinosaurs in Late Cretaceous Europe. So you have this interesting sequence of ecosystems where you've got unusual populations, unique lineages that are present and lineages that feel like they should be there but don't seem to be there. Yes. This paper took a look at some new material of a dinosaur and discovered that this diversity is maybe not what we thought it was. Ooh. This paper focuses on a skull material of one of those rhabdodontians, one of those sort of mysterious iguanodontian-like dinosaurs called Oikoceratops from the late Cretaceous of Hungary about 84 million years ago. Now, the name Oikoceratops does make it sound like it is a horned dinosaur, and it's named that because when it was originally described in 2010, it was identified as a ceratopsis, that this was a horned dinosaur, but this was disputed over time. Other researchers have come in and said, no, it looks like it's one of these rhabdodontian dinosaurs. Part of the confusion came from limited remains. Originally, it was only known from partial snout material. This new paper is describing more complete skull remains. So now we have more of a skull of this animal. Looking at this skull, they were able to identify a number of distinctive features, including the high roof of the mouth and a hooked beak at the end of the mouth, along with other features that are distinctly horned dinosaur features. That this does not appear to be an Iguanodontian relative. This is a relative of Triceratops. This is a horned dinosaur. With this information, they plugged the details into a phylogenetic analysis to sort of computationally compare species, see where they fall out, and the phylogenetic analysis agreed, yeah, this is a horned dinosaur. But not only that, in their phylogenetic analysis, some of the other rhabdodontians also came out as horned dinosaurs. Oh! So, for example, there's a species, a genus called Machlodon, known from Austria and Hungary, which their analysis found is the same as Oikoceratops. So, also Ceratopsian. There's also a few species of the genus Zalmoxes, which I think we've talked about on the podcast before. And one of the species of Zalmoxes came out as a Ceratopsian in their analysis. And when they took a closer look, they found that it lacks certain features that would link it to Iguanodontians. Okay. So they actually went ahead and renamed that species, and it is now Pharynxeratops, named after Franz Napcha from episode 106. Oh, hey. All of this seems to suggest that, A, some of those Rhabdodontians that have been a little bit mysterious appear to be horned dinosaurs, actually. It shows, if this is all true, that horned dinosaurs are in late Cretaceous Europe. and in fact kind of all over the place. There are a bunch of them. They describe it in the paper as a substantial hidden diversity of horned dinosaurs. They were right in front of us, but we didn't recognize what they were. Part of the reason why we haven't recognized them might be because late Cretaceous Europe is so unusual. You have these unusual ecosystems with this unusual composition. But if these are Ceratopsians, that makes Europe fit a lot better into the late Cretaceous world because Ceratopsians and Hadrosaurs or, you know, the Ornithopod lineage being together is pretty much the default for the other northern continents in the late Cretaceous. That's what you would expect to see. Also, the fact that Ceratopsians are present in Asia and North America, Europe is a very likely transit point for what connected those two continents. So this actually does fill in some nice gaps, if it is the case. There should have been horned dinosaurs here, and this paper is saying, yeah, there are. We just missed them up until now. Very neat. it's always exciting when we realize that the fossils we've had actually are the missing pieces we've been looking for we just didn't have enough or did not have the research tools yet or whatever it was that led us to not realize that's what we've been looking for and it brings up the question for me of were these you know because it sounds like that even with this analysis, the remains are still pretty patchy, you know, not nice, pristine skeletons. Were these weird ceratopsians, and that's why it took so long for us to recognize them? Yeah, I get the impression that they're not like triceratops ceratopsians. Yeah. You know, they're probably, or I assume they're smaller. I don't actually know. I didn't actually look at those details. But I assume that they are, I'm picturing protoceratops. seratops. Yes. Which might not be quite exactly what this is, but something a little bit less recognizable and iconic. Yeah. The other reason I wonder if they were weird is they were also potentially island seratopsians. Mm-hmm. So it's like, yeah, were you adapting in a way that we don't see as often in others, so you did not have as many or as obvious seratopsian features. Very, so not only did we find a missing diversity, but it might be a unique diversity because we got a whole bunch of islands that might be doing weird stuff. Yeah. Well, and this is also, it's a great example to put into context whenever we talk, because you'll talk about like, oh yeah, this group of dinosaurs isn't known from this continent. Yes. And anytime you have a statement like that, there is almost always somewhere in a museum cabinet. There's a specimen that they're like, except that one might be that. Yes. Yep. That one we're not sure because we are looking for that. Yes. We expect it to be here because it's everywhere else. And if you talk to an expert in that field, they're going to go, yeah, there are actually a couple of them. Yeah. But we're not sure if that's what they are, but people are suspecting enough to have gone, hey, this might be it. I don't know. It's a chunk of bone. this might be the first one and you have to wait until you know you find something better well and you'll get the thing where like the research will be like i think yes but the chunks we have are not quite enough for us to do a solid paper off of but i i'm 98 i but i need a better specimen to actually be able to confirm it that that happens a lot i've talked to a number of paleontologists where it's like is this known and they're like well like officially no because there isn't actually enough material to publish that like to be convincing for the scientific literature but speaking as a person who's been working on this particular thing for 40 years i'm i'm so confident that that's what this is and it's just like all right that yep and then you'll see it in a paper and it'll be like, these are probably present according to personal communications with this expert. This guy thinks that they are actually there. It's like we'd get that question at the fossil site where they're like, is this a new species? And a lot of times we'd be like, probably, but we don't know yet. Officially it is not new yet. Yes, but we haven't done the research to identify what species it is, so we don't know. But if I were a betting person, yeah, probably. So, listen, Europe, you might be getting your own horned dinosaurs. That's pretty exciting. That's excellent. Yes. Because if you're going to miss a group of dinosaurs, that's a bummer one to miss. That's a real bummer. Listen, over here in the U.S., we're rolling in them, and they're great. It's fantastic. We're just drowning in horned dinosaurs. Well, hey, you know what horned dinosaurs eat? plants. And you know what there was a lot of in the archipelagos of late Cretaceous Europe? Water. And that brings us to the end of our news section. And we're going to take a short musical break and come back afterwards, joined by an extra voice, the voice of Dr. Ali Baumgartner, paleobotanist to the stars, to tell us about aquatic plants. It's going to be good. Don't go anywhere. Don't touch that dial. Stay tuned. Hello, Allie. Hello, David. Welcome back to the podcast. A pleasure as always to have you. I'm thrilled to be here. Hi, Will. Hi, Allie. Allie has to whisper so as not to break her body. That is true. My breather is lightly broken. So Will and I will do our very best this episode to not make Allie laugh. We'll see how that goes. It's going to go great. I mean, according to certain reviews that we have, we're not very funny, so that should be easy. All the laughs are fake, so we just have to not do that part. We're really forcing it, so not doing it should be really easy. Allie, you are here today to regale us with information about aquatic plants, as requested by many of our listeners. I would love to start this discussion by you explaining to us what an aquatic plant is. What counts as an aquatic plant? That is a great question. Well, thank you. And as I was like digging through the literature and double checking things, yeah, the concept of an aquatic plant is lightly contentious, I would say. So broadly speaking, these are plants that are specialized to survive prolonged inundation. So oceans, lakes, rivers, wetlands. The definition from the Aquatic Dicotylitans of North America textbook, which is massive, and it's just North America and it's just dicots. Anyway, that definition is taxa capable of perpetuating their life cycles and continuing their existence in still or flowing standing water or upon inundated or non-inundated hydric soils. They can have their feet wet and not just survive, but also complete their life cycle. I guess this is a tricky, because we've talked about this elsewhere on the podcast about aquatic animals, and that it can be a little tricky because basically all animals can be in the water. Most animals can swim, animals hold their breath, and plants, obviously plants can get rained on a whole bunch, they can be covered in water. So I assume that most plants have some ability to survive being covered in water to a degree. To some degree. You know, some are obviously better at it than others, but even not aquatic plants can typically handle some degree of inundation. But again, it's the how long, how much, how often that's really going to be the deciding factor. So these are plants that are specialized to, you know, be in these situations all of the time. There are a couple of terms that you'll see associated with this. So one of them is hydrophite, which is, I think, a very obvious, you know, etymologically, it makes a lot of sense, right? Hydro water fight plant. It's a water plant. We're going to get into this a little bit. Initially, I'm going to talk a little bit about algae. But, again, we'll get into it. We'll get into it. But when I'm talking about aquatic plants, bear in mind that aquatic is technically freshwater. Marine is marine, saltwater. Sure. But when I am talking about aquatic plants, that is going to include marine and freshwater. So I will specify if I am talking about just freshwater or just marine. But by and large, I'm going to be speaking generally. Yeah, great. If I may, a little extra question for you just real quick. What is it that happens to a non-aquatic plant if it gets inundated? Do you want to talk about this now, or do you want to wait until I talk about the pros and cons of being aquatic? Oh, great. Okay, fantastic. This is going to come up. It will. I have a plan. Fantastic. All right, the short answer for now is they probably die. The same thing that happens to everything else. Yes, do you know what happens to a tree when it gets covered in water? All right. Well, let's get then into aquatic plants. So what kind of diversity are we talking about? I can think of a couple of different aquatic plants off the top of my head. How common and diverse is this lifestyle for plants? I need to immediately get really pedantic. what else are we here for exactly a penantre that is our way so i'm going to teach you some quick terminology that i love to use and i am going to use so i have to define it first so sensu lato sensu stricto amazing so sensu lato means in a broad sense sensu stricto means in a strict sense. So if you are talking about plants, plantae, since you stricto, so plants in a strict sense, green plants, verita plantae, includes land plants and green algae. Okay. Algae is aquatic. Yeah. Like that's kind of the whole thing about algae is that it's really good it being aquatic and like mostly aquatic. So I have acknowledged the existence of algae. So now we are going to talk about, so embryophyta plantae sensus strictissimo, so in the strictest sense, so just land plants. Right. Listeners, sending your requests now for an episode where we force Allie to talk to us about algae. Yeah. I really had to work around algae in this episode. No hate to algae. Love to algae. The whole history of Allie's appearances on this podcast is just dodging the topic of algae so we don't have to get into it. Ignoring the algae in the room. Yes. Yes. It's always there. Okay. Literally, my day job is also avoiding algae. So this is just par for the course. But no, because if you include algae, it is an entirely different picture. Right. because, you know, so land plants evolved from algae. Algae today are aquatic. So that is its own thing. So I have acknowledged the existence of algae. Now we are going to talk about plants in sensu strictissimo, in the strictest sense. We are just talking about land plants. All right. So now that we've oriented ourselves on the tree of life, aquatic plants have evolved from very different genetic and ecological backgrounds. backgrounds. So this has evolved so many different times. Normally, this is the part where I would make you throw out numbers. But even I know how unfair that is at this point. So instead, I'm just going to blow your mind with some numbers. Okay, so like I just mentioned, this has evolved multiple times throughout the evolution of every group of land plants. So some of these groups are aquatic at an order of family level, which means you're going to have a whole bunch of species or interrelated genera that are all aquatic. But others, so things that have evolved a little bit more recently, are going to be isolated species within genera, or even certain varieties or populations within species. So this is something that is still evolving. Plants are still going to the sea. Well, less the sea, more freshwater. The rivers. The rivers, the wetlands, all of those places. So inland plants, aquatic species are found in 103 families, more than 440 genera. It has arisen, and this is the reason I am not making you guess, because again, it's been found in all of these groups. It has arisen at least 222 times. Yeah. But it could be as high as 271 or more. Amazing. Yes. Other than the scale, I'm really loving how much this is paralleling the secondarily aquatic. Yes. tetrapods that we talked about in that we had to do the same thing of aquatic vertebrates includes fish which is redundant but we're gonna so we're gonna exclude that we're talking about amniotes that came to land and went back and similarly here you have to make that distinction well i was actually thinking about this that specifically the whole time that i was going through this episode because I am bilingual in vertebrate paleontology and paleobotany. So I am familiar with both of these, the evolution of triestiality in both of these groups. And on so many levels, there's a whole lot of similarities. And so it's also not surprising that when they go back to the water, again, you have a lot of similarities. Yeah. And like, then there's a huge diversity. It's much greater in plants, but it is still notable that there is such a trend in heading back to the water among land life, which is very cool. Like we've talked about before, this planet is covered in water. Yes. So on the one hand, it's not that surprising that so many lineages went, you know what? Why don't I live in the other 90% of the surface? Right. Yes, exactly. diversifying, you know, diversifying your portfolio is, you know, really important. And also getting back to your roots. I appreciated that. I just can't laugh because it hurts. All right, fair. Okay. Imagine that I laughed at that. That's what I do anyway whenever I tell a joke, so. I would have laughed too, but it hurts. That's why I didn't laugh. Oh, my gosh. Oh, my goodness. So every group of land plants has at least one aquatic species. So, all right, we're going to just briefly go through all the different types of land plants just to acknowledge this. So in liverworts, hornworts, mosses, these are your non-vascular plants. They're actually shockingly terrestrial. So they require proximity to water, but they would prefer not to be inundated by and large. There are plenty of aquatic species, but they are mostly terrestrial. So there are roughly 11 families and 22 genera of aquatic plants. And this secondarily aquatic nature arose 10 to 19 times. This is going to be a trend. Well, it's like even in the group that you start by saying they mostly like to hang out on land, they only went back to the water like almost 20 times. Yeah. A handful, you know. So ferns and friends, so ferns and fern allies, I have talked about the ones that are aquatic before. So there are nine families in 11 genera of ferns and fern allies, excuse me, that are aquatic. And this arose at least seven times. So, gymnosperms. This one is interesting because until relatively recently, we did not think there were any aquatic gymnosperms. Okay. How foolish we were. I was wondering because I couldn't think of any. I also until recently didn't think that there were any aquatic gymnosperms. Very, quite recently. Quite recently. Undersea pine cones. So the prevailing wisdom, in fact, many textbooks said that gymnosperms were hydrophobic, which initially should, some alarm bells should go off for that because of like, you know, all of those, you know, Cyprus and all of those friends that like, is that not aquatic or at least aquatic adjacent? So they're not technically, again, depending on certain where you draw the line of aquatic. They're not, but they're definitely not hydrophobic. Like those are very much water loving plants or at least water tolerant plants. So there is a single species. It's Retrophilum minus. So this is a podocarp as a small tree, three meters to 10 feet tall, not getting taller than that, endemic to New Caledonia, which is very funny because the only species of parasitic gymnosperm is also a podocarp, also endemic to New Caledonia. That's where gymnosperms go to get weird. Exactly. So this is a tree, like I mentioned, and it is a type of aquatic plant called a raophyte. A raophyte is an aquatic plant that lives in running water. So like, you know, flowing water. So this is found in lakes and rivers in this part of New Caledonia. Okay, so a final group of land plants, the angiosperms. There are so many aquatic angiosperms. Before we recorded, you named multiple for me. Yep. This is also the only group that lives in marine environments. So no other group of aquatic plants lives in marine environments. So that is the seagrasses. It is, in fact, in the name. Yes, the only marine plant. Yes. Sensu strictissimo. Yes. Yes. Exactly. We are not counting algae because algae aren't actually marine plants, but it's fine. It's fine. Algae is just like, what do we need to do? I'm right here. I feel about algae a similar way that I feel about fungi. That, like, they're so cool. I'm so sorry. I'm excluding you in everything that I talk about, but you do complicate my story just a little bit. Yeah, understandable. Which is why we did three massive episodes on fungi because they didn't get any other attention. So in angiosperms, there are 83 families and 407 genera of aquatic plants. So the majority of aquatic plants are angiosperms. And the aquatic lifestyle arose in angiosperms 205 to 245 times. And this is why I didn't make you guess. Yeah, it's really crazy that earlier when you were like, there's over 400 groups of aquatic plants. And it evolved over 200 times. And then you listed all the other groups, and we still did not break below the 4 or 200 when we got to angiosperms. Right. That was just the over were the other groups. Yes. Yes. That is a statistical, like, error. The overburden. Yes. Yes. Ridiculous. Absolutely. And this also does make sense because, you know, so much of the diversity of plants today are flowering plants. So, well, it's unsurprising to me. I say that. Maybe surprisingly. We'll find out based on your reaction. I plan to be surprised. You know what? I should have expected that. Aquatic plants have a global distribution. What? Wherever you can have plants. What? you can have plants and water and water you can have aquatic plants well because like personally i was like you know you why would you must not have aquatic plants in like alaska absolutely you do like up into the boreal forests so basically where you can have plants and where you can have water you can have aquatic plants so unsurprisingly this one is genuinely unsurprising The greatest diversity is, in fact, in the tropics. Yeah, that I'm not surprised by. Right. But so especially in South America, but also like South and Southeast Asia. Right, yeah. Which, again, these are the places in the world where you're like, yes, there's a lot of diversity there. Unsurprising that that would also be true for aquatic plants. But we'll get into in a second the pros and cons of living in different places as an aquatic plant. Sure. Sure. And it makes like also the tropics, the two terms that always come up is warm and wet. And if you're going to be in the aquatic plant, that feels like the place to be. There are some downsides to warm in the wet, though. So aquatic plants are associated with permanent water bodies. So rivers, lakes, wetlands, oceans. And again, this is the whole argument of what makes it aquatic. Right. So like ephemeral ponds, seasonal ponding is does that fall under that? Again, we like to argue about boxes a lot. Yes. So I did not realize how widespread the distribution of seagrasses is. I was just wondering if you had made me guess because I associate seagrass with manatees. It's like Florida. It's like, I don't know, the Gulf of Mexico. And that is where my guesses would have stopped because anything else was just speculation. So I looked it up. I looked into it because I was like, I need to know this because someone's going to ask me. I was going to ask you. Exactly. I'm so ready. I've done enough of these that I could kind of predict some of the questions. So like I said, globally, a lot of times they tend to be on the east coast of continents. You'll get them on both sides, but a lot of it is on the east coast. So temperate North Atlantic, so both sides of the Atlantic, the tropical Atlantic, but this is primarily on the South America side, the Mediterranean, the tropical Indo-Pacific, and the temperate Southern Ocean. So the west coast of Africa does not have very much seagrass at all, which is interesting to me. I mean, in that case, it does make sense that that's the opposite of the direction that, you know, like the water is flowing, right? Sure. You're getting the currents coming back down south over there. Yes, exactly. So that does make some degree of sense, but it's like the only bald spot on the map for seagrasses. Yeah. So a little strange. So a couple of fun examples that I will give you some fun facts about a group you do know. And some fun facts about a group you don't. Do you want to start with the one you do know or the one you don't? Let's start familiar. All right. Yes. Sounds good. All right. Seagrasses. Great. Okay. Seagrasses are not grass. Oh. I didn't think they were. Oh. All right. Apparently, I didn't know them as well as I thought I did. Right. You think you know a plant. I used to know them better because we talked about them at the aquarium. because we had the Manatee Viewing Center and talked about the importance of seagrasses. And I felt like I remembered that being one of the facts is that its name is a lie. Yes, it is very reminiscent. So seagrass isn't grass, but it is a plant. Yes, it is. For anyone out there who is wondering why we haven't mentioned seaweed or kelp yet, because seaweed and kelp are not plants. Those are algae. Those are different. They're algae. I mean, technically they are plants, but they're not landslides. Again, it's fantastic. Seagrass is a plant. Strictly speaking, it is a plant. Yes. But not a grass. Correct. It is a monocot, though. All right. All right. So you'll give it that. So it's grasses are in the order Poelis. This is in a different order, Alyssimoteles. And there are multiple families that are all in this order. So they are, as I mentioned before, the only marine land plants. They are, unsurprisingly, and this, again, I think is going to be unsurprising for you, restricted to the photic zone. Because you know what plants do, they photosynthesize. You got to have the photic for the photosynthesis. You don't really get, not really a lot of dark adapted plants. Not, not really. But the leaves lack stomata. Okay. Yep. Makes sense. Yeah, they don't have the stomata. You know, sometimes you write the outline, right? You fill in the outline. You're like, this is the thing. This is the moment that I'm like, this is going to blow their mind. They were thought to be pollinated by currents, right? Just releasing the pollen into the water column and it goes where it goes. Recent research shows that they have animal pollinators. Yeah, I was wondering. crabs, polychaete worm larvae. Yay! Larvae in the ocean, that's the way to do it. Stick your pollen on the plankton and just have it float around. Exactly. So the plants produce nutritious, musogenous clumps of pollen. So basically sticky, nutritionist clumps of pollen to attract and stick to the animal pollinators. Fantastic. That's awesome. I've never for a moment considered how marine plants would pollinate. Yeah, honestly, same. I had never thought about it before. Again, like I said, when I found that, I was like, this is going in. This is going in. Do they have flowers? I believe they do, but I believe they're highly modified. I did not look into that too deeply. They have to have something, given that that is how flowering plants work. Yeah. But so many morphological features, so many characteristics of aquatic plants are super, they're weird. They're weird. They've done so many things with their morphology. And we'll get to that actually immediately with this other group. So you haven't heard of this group. So this is the family Pedastomacy. Oh, Pedastomacy. Yeah, obviously. I know a George Macy. Basically the same thing. So my counterpart, the other collection manager of vascular plants, Brad Rufel, he is an expert in podosomacy. And so I made him talk to me about podosomacy yesterday. I was like, tell me what I need to tell people. And he got really excited and brought me a book and everything. And it was great. So the first thing, so the common name is river weeds, which is unhelpful in terms of a common name. So they are found primarily in the tropics or the subtropics. I think there's one species that goes, it's in temperate North America. The first line of my note says weirdos in all caps. So these are the kinds of plants that are often mistaken for algae. So a lot of the times when you will come across a Podosomaceae in a herbarium, they may be categorized as algae and they're going to be moved over to the land plant. So they're so weird looking. So they have a lot of ambiguity in their organs. So identifying their roots is one of the ways that you identify them. But it can be difficult to tell the difference between the roots and the shoots. which seems like, you know, when you interact with plants that have very obviously differentiated roots and shoots, the idea of like, what do you mean you can't tell the difference? It's a little confusing. So they are one of two families with this very particular lifestyle. The other family is a single genus that was actually originally classified in Pedosomaceae because their lifestyle is dissimilar. So they, if you're a geologist, these are the plants for you because they are, I get real excited about them because they are so firmly attached to the rock that you, you, they are often collected with the rocks, which is really fun. So, you know, like we recently got a big, a big collection of them. And yeah, it's just a little box with rocks with green smears on them. so they are attached to these rocks in these tropical rivers in south america primarily and they need rapidly running water so either river rapids or in waterfalls they can't handle silt it has to be clear running water um like i said they're cemented to the rocks and they require changes in water level in order to complete their life cycle so they spend most of their time completely submerged. They're really important food for some young fish or the tadpoles of like the goliath frog. But as the water levels drop and the waters recede, the plants are no longer submerged, then they can flower because they don't want to be submerged. They want to actually distribute their pollen in the air. And so then when the water level comes back up, that, you know, after they've fruited, flowered and fruited and everything, then they're good. But there are, like, so that change in water level is required for them to reproduce. Yeah, so they're kind of like sea turtles. Yeah. They spend their lives in water, but they have to leave the water to release their offspring. But sea turtles can move. Yeah, well, you're cemented to a rock. Yeah the idea that you require changing water levels to move in and out of the water That very interesting And that means that dams really ruin their lives Yeah. A lot of them are endangered or threatened, and a lot of it, you know, due to habitat loss. And some of it is just as simple as with dams, you don't get these drops in water levels like the plants need, and they can't reproduce. Yeah. So, yeah, even though the plants aren't dying, they are not perpetuating, and that's kind of the same thing. Yeah. Yeah. It's fascinating to think about the diversity of aquatic plants just off the top of my head, because we've talked about plants that are fully underwater, the seagrasses. We've got plants that go in and out of the water, like these river weeds. The other thought that always immediately comes to mind are, like, water lilies. With their lily pads, which float on the surface of water. You are doing such a good job of leading into what we're going to talk about. And the other one that came to mind is, and here we're in that blurry area, mangrove trees. Which, as far as I understand, root under the water. Right. But the tree, it is an emergent aquatic plant, perhaps. well i know i know terms okay i know terms i just don't know how to apply them that is a term that is a term yeah so oftentimes mangroves again mangroves are in this like in between like is it aquatic is it just good at living in like it like wet soils again it's man we're fighting i mean that That is kind of the definition of mangroves is in between environment. Like that's kind of their whole shtick is being in between stuff. Yes. Well, I'm sure that we will have more examples as we continue to discuss aquatic plants and their lifestyles and such. For now, let's get into the question of what unites aquatic plants. What are, and this gets me back to that question before. Most plants don't want to be underwater. Correct. So what are the major challenges that face aquatic plants? What happens to a plant when it gets covered in water? Exactly. So one of the papers that I read was a little bit sassy, and I really enjoyed that. I love when you get like the flavor from an author. And he made a joke that to understand the difficulties of evolving an aquatic lifestyle, one must read the chapters on becoming terrestrial backward. Yep. Which, I mean, there's some truth to that. But they also suggest that making an embryo may be the primary terrestrial trait that is retained by all land plants. So as aquatic plants get barely recognizable as plants in some ways, they still retain the embryo. So, for example, wolfia is a flowering plant. So it's an angiosperm. It is less than one millimeter long, and it has no differentiation between root and shoot, and it has no vascular tissue. So it's just a blob. 100%. It is absolutely a blob, but you know what? It makes an embryo. Okay. So there are some pros and cons to aquaticness. Let's lead with pros. Water. Bingo. So much. You never have to worry about getting a drink. Bingo. Because so many adaptations that plants have are to conserve water. Yeah. And if you are just living in water, that is not a concern. It's water, water everywhere, and it's awesome. It's great. Yes. You can drink it. The other big pro is maybe not one that you'll think of immediately. Buoyancy. Oh, you don't have to grow up as much. You don't have to grow up. You don't have to grow like stiff tissues like lignin. You know, to support yourself. Uh-huh. Because the water will do that for you. And there is some, like the way that plants actually address this is definitely very variable. But in general, you're getting more help holding yourself up than the atmosphere would give you. Yeah. You don't need to be a tree. Yeah. Yes. Right. We've talked before about how that is the thing about trees. The thing that makes trees so successful and incredible is that they built themselves a plant skeleton. Exactly. This incredible skeleton that allows them to grow tens, hundreds of feet tall. If you're in the water, you can just float there. So the evolution of plants coming on land, and I'll talk about this a little bit more in a bit, but one of the big innovations was this ability to grow in a direction, right? To, like, you know, follow gravity, all of these things, because you need to be able to orient yourself on land in a way that you don't so much in the water. Yeah. Yeah. So the presence of water and buoyancy are two really big pros of aquaticness. And also just, I didn't write this down. I can't believe I didn't write this down. It's just more options for places to live, right? Yeah. There's a lot of fresh water. There's a lot of fresh water. There's a lot of salt water if you're down with that. Sure. I would also imagine that being aquatic gets you away from a lot of the typical plant predators. Yes. Well, obviously there are things, like we mentioned manatees, and obviously there are lots of aquatic animals that eat, you know, algae, seaweed, whatever. Yes, yes. But typically aquatic things are not eating true plants in the water. Yeah, I would be curious. I am purely speculating at this point. I would be curious about the, because one of the big predators of plants are insects. And I would be curious about, you know, if aquatic plants are, you know, more protected from predation from herbivorous, you know, insects. I'm very curious. I don't know the answer to that. There are a lot of aquatic insect larvae. That is very true. Yeah. But are they herbivorous? Yeah. Also frog larvae, which are often herbivorous. That's true. Okay, I'll give you that one. And lots of crustaceans. Lots of your things like that. I know nibble on plants. You could just distract them with the algae. Yeah. But you don't get a lot of large-bodied herbivores in the water. I mean, you do get some. That is not a common. But moose will do that, right? Yep, yep. That's true. And then, you know, managing. I guess water, especially if you have to stay where it's light, a lot of animals will just kind of go down there and get you. I mean, moose have such long legs. Yep, yep, yep. Yep. So these are the big, like, main pros for aquaticness. The cons of aquaticness. Air. Air. moose moose you know weirdly i didn't include moose but yeah so plants need light oxygen and carbon dioxide all three of these things are a little more difficult to get in water than just from the air so photosynthesis is therefore more easier, more, you know, it is way easier to photosynthesize on land because you don't have this, you know, extra layer of difficulty. Because here's the thing that I was kind of alluding to before. So water in general has less oxygen, less carbon dioxide in it than air. Warm water has less in it, like has less gases, you dissolve gases in it than cold water. And flowing water has more than stagnant water. Yes. So if you have warm, stagnant water, that is hard mode. Yeah. But if you have flowing, cold water, like, let's go. Which, once again, is very fun because these are the same difficulties that we've talked about fish and marine and aquatic life having. Yes. This is why fish in a still lake you will see come up and gulp air because there's none in the water. This is throwing me back to when I was doing my PhD. I taught a class called, it was called World Oceans, but really it was a global water class. And I have taught many an undergraduate about the fact that there's more dissolved oxygen in cold water than in warm water. Like, I'm very comfortable teaching this to people. Us Earthlings, we are all at the mercy of chemistry. of basic chemistry. Absolutely. I think that one often surprises people because when it comes to dissolving soluble things like sugar, it's the opposite. Hot water will dissolve more sugar or whatever thing you're wanting to mix into your drink than cold. That's why if you want to make iced, you know, tea, like sweet tea, like cold sweet tea, you have to brew it hot, mix the sugar, then cool it down, or else you won't be able to mix the sugar in. Or have a liquid sugar. Yes, yes. But trying to do a solid into the liquid. Yes, exactly. But if you think of, like, a carbonated drink. Exactly. There's way more carbonation in a cold drink than a warm drink. Yes. Gas behaves differently. It's almost like it is a different phase of matter. It just has to be difficult. That's my take of it. I agree with that. And then the last option, the last con of aquaticness is pollination is trickier. You have more options for pollination methods in the air. You can use wind. You can use animals. Clearly, you can use animals in the water, too, but it is a little bit trickier. So, I mean, you win some, you lose some. There are definite tradeoffs. and clearly a lot of plants gave it a go. It also seems like pollination would have a drawback because if you're in a lake, you can only pollinate really within that lake. Like pollination in the air can travel miles potentially if it's on the wind or, you know, on a bee. But in that lake, you're kind of stuck in that lake. And this is why a lot of aquatic plants, I'll talk about this in a little bit, but they may be have parts of them above the water or may have be above the water for parts of the year to try to capitalize on that. Because the whole thing about pollen is that it is meant to be dispersed. And so if you are, you know, limiting yourself to like a pond or something like that is defeating the purpose of the pollen. So I was reflecting on, you said the big pro of being aquatic. And I said water. And you said the big con of being aquatic. And I said, air. And I was reflecting on that, and I came to another pro of being aquatic, fire. No, that's true. Or a con, depending on what plant you are. Correct. There are plants that need fire in order to reproduce, so they would not be happy in an aquatic setting. Go listen to that episode of Leave It to Us, all about fire. I was like, I talked about this. You did. I believe it does. So is me. All right. So how do aquatic plants then evolve to overcome these challenges? What are the sort of typical or shared adaptations that we see? This is – I had to rewrite this part of the outline multiple times just to figure out how exactly to talk about this, to categorize it. Because, you know, scientists, we love a box. We're like cats, right? Just like so pro box. Yep, yep, yep. So I found a set of boxes that I like, and I'm going to broadly go over them because the trouble is, or not trouble, the reality is, you know, it's biology. There's not boxes. It's just a spectrum, but it's like multiple spectra on multiple axes because biology. So here are some broad categories of types of lifestyles within the framework of aquatic plants. And we'll use this to kind of talk about, you know, broader characteristics. So first category I'm going to acknowledge are the amphophytes. So these are your amphibians of plants. So they can live either submerged or on land. So they can, you know, whether or not they count as aquatic is debatable and is variable. And this is the category that people seem to, like, get hung up on just because, like, is it? You know, not everybody, you know, not every part of the species may react the same way. But, you know, with that definition of, you know, they can. They go through their lifestyles. that can continue their lives in either wet soil, inundated soils, or actually submerged. Yes, these totally count. The next one are the reophytes that I mentioned. So these are plants that are specialized to live in flowing water. And it is interesting, as we'll get into in a second, the speed of the water, whether or not you have flowing water or more calmer water, is going to impact the kind of adaptations that you have. so you have the elodeids so these are stemmed plants that spend their life cycle submerged or they just have flowers above the water you have your isoatids these are rosate uh or excuse me these are rosette plants so basically just like you know around around plants uh so without a stem that spend their entire life cycle submerged. There's the heliphytes. So these are plants that are rooted at the bottom with their leaves above the waterline. So when you said emergent aquatics, this would be an emergent aquatic. I love emergent aquatics. But then you have your nymphaeids. So these are plants that are rooted to the bottom with floating leaves. Again, different category like we discussed earlier. And then you have, there are plants that float freely in the water. So not necessarily floating on the water. You have some that are floating on the water, but some just might be like, you know, in the water column itself. With oftentimes they'll just have like hanging roots, not attached to anything. Just dangling in the water. Yes. Yep. Yep. I knew of those because I've seen those in aquariums because they're very popular as surface cover in aquariums. Yes. Let me tell you, when I was trying to Google things, I got so much aquarium information. Like, no, no, no. Yes. Welcome to the struggles of trying to look up things that aquarists are interested in. Oh, my God. I struggled with that all the time when I was like, oh, I want to learn about this species. And they're like, this species is really popular and pretty. No, that's not what I care about. No, I absolutely ran into that problem when I was trying to look up, like, specific species, right, that are common in Aquaria. Or when I was trying to get in the weeds, literally, of the relationship between plants and oxygen. Oh, yeah. You'll learn a lot about filters. Oh, my goodness gracious. Yeah. So anyway, broadly speaking, there are some characteristics that are common amongst aquatic plants, but there are many ways of being an aquatic plant. And so some of the things that I'm going to mention are true for some, may not be true for others. So just broadly speaking, here are some things that you might see in an aquatic plant. So one characteristic that is mentioned a lot are the fact that they often have finely dissected leaves. So either just very narrow leaves, if you think about seagrasses, or they're like very like wispy leaves. Some plants will have two different leaf morphs. So they'll have the finely dissected leaves below the water and more leaf shaped leaves above the water. Oh, cool. And part of that is just because, like, it's more hydrodynamic, right? That way you're not fighting with the water so much. You're just kind of chilling, man. You're not. Your leaf isn't shaped like a sail under the water. Yes, exactly. Or an oar. Or an oar, yeah. Yes. Exactly. So they do tend to be rooted in the substrate or they have roots that are dangling in the water. But there are plenty of floating plants. So again, getting into those like really little ones, your pond weeds sort of things that are going to reduce their roots and shoots and basically be just like little photosynthetic blobs. submerged plants, so ones that are entirely below the water, tend to have soft and flexible stems so that they can just go with the flow literally of the water and don't have to worry so much about being, you know, battered and pushed around. On the other hand, emergent aquatics, like if you think about like cattails, like those sorts of plants that are, you know, have stems that are coming out of the water, those stems are going to tend to be much more rigid in order to, because they have to withstand the water that they're in. I believe I've mentioned this at some point in the podcast, but aquatic plants have a type of tissue called Arranchyma. So this is spongy tissue that has air channels that go through it. And this allows plants to exchange gas through their tissues. And this is especially important for, well, it's important in general, but emergent aquatics will use that so that they can collect gas above the water and it can be used below the water. Oh, yeah. Because plant vasculature, right, your xylem and flood, your plant blood vessels, as it were, are transporting water throughout. the plant, but they're not transporting gases. Yeah, they super don't want that. Like you don't want bubbles in your vasculature. No, typically you don't want air bubbles in your vasculature. No, no, no, no, no. That's real bad. That's real bad. That's an embolism. Yes, that's how you explode. Yes, that is how you explode. That's really interesting. That's another thing I would not have thought of as a challenge is how do you get the gas all the way down under the water? Yes, exactly. Well, especially because roots are how land plants, like terrestrial land plants, get a lot of their oxygen. But that's trickier for aquatic plants. They can do that to some degree, but it's, again, like being an emergent aquatic, I think honestly sounds like the best situation because you are able to capitalize on, you know, this terrestrial environment that your, you know, your group evolved for while also getting some of those perks associated with being aquatic. Another interesting thing that I got really hung up on, so I was glad I was able to find some sort of answer. So dissolved gases. It's difficult. So water is H2O, but that is not O that the plants can use. So you have to have dissolved oxygen. Dissolved carbon dioxide is often a limiting factor for plants. So they will, there are a lot of submerged aquatic plants, so the ones that are completely under the water, that are able to get carbon from bicarbonate ions. So they're getting their carbon from a different source. You know, same purpose. All you need is carbon. The oxygen is a little bit easier to get, but yeah, to get the bicarbonate. crack off the carbon and do it that way. And it's bicarbonate. So technically, that's more carbon. And then the last one I kind of mentioned, so reophytes, these plants that are living in flowing water, they need to be pretty rigid in order to withstand the fast flowing water. They also tend to have spreading root systems to support them. Sure. They have a wide base, you know, a wide stance. Yes. Well, that's why those river weeds you were telling us about are just smeared onto rocks. Yes. Yes, exactly. Because they're living in these really, you know, high energy environments. So there are a lot of other, like, very esoteric characteristics that are associated with aquatic plants. Like some of the papers that I was reading is like, oh, I do not know how I would explain what this very specific thing means. But I think the biggest thing to bear in mind is that they're unlike some of the other groups that we've talked about. Right. Parasitic plants. There's pretty much one way to be a parasitic plant. Sure. That is super not true for aquatic plants. There are a lot of ways. And part of it is because of how many times at how many levels and how many different groups this aquatic lifestyle has evolved. They're coming at it from so many different directions. And it's so many different types of environments. Right. You have your tropical wetlands, which are different than temperate rivers, which are different than Arctic, near Arctic wetlands. And then that's always all going to be different than the ocean. So we have all of these different groups. So when I was trying to put together like characteristics of aquatic plants. Yeah. Well, like talking about characteristics of aquatic animals. Yes. It's like, well, yeah, there's a million of them and they do it a million ways. Yes. A couple of questions come to mind. One that I've been wondering is plants that float. Yes. How do they maintain buoyancy? I'm picturing because, like, kelp have those – some kelp have those, like, big gas bubbles, those, like, gas bladders that help them float. Are plants – I assume that some plants are just – they're tiny and they sit on the surface and it's not a question, or they're, like, planked in and they're just carried in the current. Some of them do have inflated leaves. Oh, cool. Water wings. Yeah, basically. Well, and if you look at, so Nora and I, I believe we're both really into this. The Water Lily Way Off is a competition between global botanical gardens where they will take these big old tropical water lilies and they will see how much weight they can make the water lilies hold. That's so what I was hoping you were going to say. Yes. And it's great. It's a really fun competition because it's, again, it's a global competition. It happens every summer. And it's wild to see. So they do, like, they show, like, the differences in sizes of their water lilies. And then they try to pack on as much weight as possible. Like, they build supports to, like, even out the weight. It's wild. Basically, some of these water lilies, you can support a person. Wow. Yeah. So the way that they do this is that, so they are these very large leaves, right, that float, but also they have this eranchyma, right? They have this spongy tissue, these air-filled tissue that allows it to float on top of the water, which is, so there's a lot of, there's a couple of different ways, right? You know, you can just be small enough, actually inflated versus, yeah, just using an eranchyma. But yeah, basically there's a lot of ways that they can use tubes to be full of air in order to float. Amazing. Yeah. That's very cool. The other question that comes to mind, and only because this is such a big deal for aquatic animals, is temperature. Yes. Is that a problem? Because water habitats tend to be colder than being out in the air because water pulls heat away from you much more effectively. which is why we see so many aquatic animals with like blubber or fat stores or dense fur. Do plants care about that? Is this a problem for plants? I mean, plants care about temperature. Yeah. But yeah, so I'm thinking about like plants in both like warm environments and cool environments, right? So you tend to get much smaller plants in the boreal environments just because, you know, there's less of you to freeze or that, you know, to be damaged by that. I think the bigger problem with temperature is not necessarily like the way that it's going to impact the plant per se, because like plants can overheat, but, you know, not in the same way I feel like animals do. But yeah, I think the bigger concern for them, like the biggest limiting factor for them with temperature is honestly just like how much dissolved gas is there? Because plants are kind of fish in that way. All right. Yeah. Cool. Yeah. That makes sense. Plants are fish. You heard it here. Plants are fish. Allie Baumgartner, 2026 by the time this comes out. Vegetarians rejoice. this has been a fascinating uh quick exploration of the diversity of aquatic plants i'm sure we've missed some people's favorites uh let us know out there if we didn't mention your favorite aquatic plants let's take a little musical break and then after that get into the evolutionary history of aquatic plants i'm very excited for what surprises await on the other half of the episode All right, Allie, let's go all the way back to the beginning. Animals started out in the oceans. Did plants start aquatic? So this gets back into the, like, pedantry, right? Of what is a plant. So because algae are plants, well then, yeah. Okay. So I'll modify the question to make it a question that sounds stupid. I love that. Did land plants start off aquatic? Okay. So land plants evolved from green algae, which is aquatic. So yes. Yes. Yes. So let's talk really briefly about what plants had to do in order to become terrestrial. Because it is, again, it's the reverse of what they're doing, kind of, in order to become aquatic. So very, very similar to animals. For plants to become terrestrial, there were three key things that they had to evolve. Protection from desiccation. So for plants, this was cuticle, right? So like a waxy covering on the leaves. and sporopollinin, which is what pollen is made out of, which is one of the most robust organic substances on the planet. Second thing that they need was an anchoring mechanism, which is quite different, actually, from what animals needed. Kind of the opposite, actually. So they need an anchoring mechanism. So for nonvascular plants, that's going to be the rhizome. for vascular plants, this is going to be roots. And then the last thing that they need are pores to let gas in and out. Because again, gas exchange is very different in air than it is in water. So this is going to be things like stomata. So the earliest land plants, so again, like the strictest sense, land plants, were non-vascular. So even after they came onto land, they needed to be in moist environments. So they were in close proximity to water, even if they weren't necessarily in water. So this is the point where I make you guess. Oh, hooray. Okay. Land plants. When do you think that land plants as a group, so like the first part of the group, when do you think the first land plants became secondarily aquatic? I'm going to stake, I'm going to make a bold claim here. Okay. I'm going to say the Silurian or the Devonian. I'm going to say that like animals, they did it almost immediately. Okay. That was going to be my guess as well. All right. Final answer? Final answer. Correct answer. That's it, Regis. Correct answer. Y'all are going to be devastated. Oh, no. Cretaceous. The Miocene. Cretaceous. Yeah, I was going to say angiosperms. That was my other, my second guess was no one did it until angiosperms did it. But that's not true either. Everybody started doing it in the early Cretaceous. What? That's when ferns start doing it, too. It was in vogue. Uh-huh. No, it's actually genuinely kind of wild because you have hundreds of millions of years of just terrestrial land plants. The plants finally caught on to, you know, the dinosaurs aren't going in the water. Yeah, they were like, oh, no, this is the last straw. Dinosaurs, that's too much. It's genuinely kind of wild because I had that same thought of like, oh, this must be an A.G. sperm thing. But, no, we're also seeing the same pattern in, say, ferns. And ferns have been around for a very long time, but they did not. Okay, that's the thing, right? Birds have been around for hundreds of millions of years. They did not become secondarily aquatic until the early Cretaceous. But angiosperms had not been around for very long by the early Cretaceous. So, like, angiosperms. I'm very, I'm fired up. But angiosperms basically went back to the water pretty much immediately upon evolution. In fact, some of the earliest fossils that we have, spoilers, there are fossils. Oh, whoo! Thank goodness. I know. Oh, that cacti was devastating for a lot of people. But some of the earliest fossils that we have of angiosperms are aquatic. So, two thoughts come to mind. One is that the Cretaceous is famous for an abundance of shallow ocean. Uh-huh. Yes. That is a very famous thing about the Cretaceous because it was high sea levels and it was relatively warm. So you did have a lot more shallow ocean area. It's not the first time in Earth history that had a lot of shallow ocean. Correct. So it's not unique. And my only other thought is, did angiosperms somehow prime other plants for, Or, like, did ferns follow angiosperms into the water somehow? This is the thing that I, like, genuinely don't know. So, yeah, like, is it something that because angiosperms went into these environments, they became easier for other plants? I genuinely do not know. Aquatic plants, there's not a great fossil record. We're going to talk about that in a second. Sure. So it is really hard to see this beginning. I wonder if there could be anything with, like, shift. Because, like, I assume in your freshwater environments there would have still been green algaes and those things growing because they grow wherever it's wet. And I wonder if there could have been any shift in that dynamic that made way for land plants to come in, like, if there was something that changed there. But that is truly, like, evolutionarily very bizarre. Yes. And so to be fair, we don't really have the fossil record of land, bryophytes, you know, mosses and friends is kind of terrible. So unsurprisingly, the fossil record of aquatic, you know, bryophytes and friends, also terrible. So we might just be missing the earlier aquatic. It's entirely possible. Well, especially since we went through periods of, like, super swamps well before the Cretaceous, that it seems like some plant would have gone, I'm going to live here. Well, and some of this, too, can be some degree of pedantry, right, of what is an aquatic plant. So even though we had the Carboniferous coal swamps, like, which is a lot of, like, there's definitely water. Like, we know that those were very wet environments, but does that count as being aquatic? Like, you know, it's aquatic in kind of the same way that, like, a mangrove swamp is aquatic. But when we're talking about, you know, the early Cretaceous, these are very clearly, like, there is no doubting that these are aquatic plants. Yeah. Once again, I'm loving the parallel between the animal discussion of depending on how you define it depends on who's the first and when it happened. And I mean, yeah, we're having a marine revolution in the plants, too, in the Cretaceous. Yeah. You have already answered the most dramatic question of the episode, which is, are there aquatic plant fossils? Yes, thank goodness. Thank goodness we can keep having the podcast. Which shouldn't have to be a dramatic question. Cacti really ruined us. It was a real problem. It's really put y'all on edge. Every plant episode. It's just like, Allie, are there fossil ferns? I'm pretty sure there are fossil ferns, but come on, tell me. So, knowing that there are aquatic plant fossils, how do we identify an aquatic plant fossil? There are a variety of ways that we can do this. So the easiest and probably the most common way is based on affinity to known aquatic plants. So basically, this looks like it's in a group that is aquatic today. Right. This is a seagrass, therefore. Right. Right. And so sometimes it's easy because you find the part that has like very obvious aquatic out of patience. Like, oh, yes, this has what is clearly, you know, it has a rank of muck. All right. This is an aquatic plant. But sometimes it's just based on like, you know, we today this entire family is aquatic. Therefore, this is likely aquatic. And there are some characteristics that if you find them like, oh, yeah, you know, this seems likely to be aquatic. So, you know, like highly dissected leads. Again, that's something that you can definitely see in the rock record. And there are other, like I said, sometimes very esoteric seeming adaptations that can be documented. Like it was in this section that I was going through that I was reading these papers. And, oh, man, I am not that kind of paleobotanist. So I will not be going into that detail. So another thing that we can do is, this is very fun. So we can reverse engineer a record of plants by looking at something else. So, for example, seagrasses. Remember those? Mm-hmm. They have an abysmal fossil record. Like, there are fossil seagrasses, but it's a truly rotten fossil record. Would you say it's an abyssal fossil record? Me? No, because there's no light down there for them. Exactly. That's fair. But Sirenians, so manatees and friends, have a better one, especially because they have really dense bones. Yeah, they sure do. They fossilize quite well. Yes. So analyses of their diet indicate that they're eating seagrass. So you can use, and they eat it today, right? So you can use the presence of Cyrenians in the fossil record as a seagrass proxy to some degree. That awesome There are manatees here ergo there must have been some seagrass around Yes exactly And it actually really interesting because using that gives a different picture of the paleo distribution of seagrasses than what we have today But again, this is like indirect, right? So you're looking at the thing that eats the grass. It's probably grass there because this is what eats the grass, but you don't actually have it. Oh, yeah, because manatees can move between patches of seagrass. Yes. They also can eat other plants. Correct. If you're ever wanting to, there's some adorable videos of them eating leaves off of trees when the water's high enough. Oh. That's fantastic. Just munching on branches that have gotten down into the water, and it's so cute. That is adorable. I'm so happy. I could cry. Another way that we can recognize aquatic plants in the fossil record is by using multiple lines of evidence. So this is what I used in my dissertation research. So in my dissertation research, I did field work in Western Kenya at some early Miocene sites. And there was one locality in particular that we had absolutely great. like we had so many different records that we could look at uh so we had paleobotany but we also had sedimentology paleopodology so looking at the fossils like looking at the sediment but also looking at the fossil soil so we could look at multiple different things and so we were able to basically take multiple different directions be like this is probably an aquatic plant so for example sometimes it was really easy like wow this looks remarkably like a modern cattail leaf um so the genus typha like okay uh this seems like a pretty obvious you know that this is going to be aquatic or pomodiguit and like other things like that and then you can combine like okay i think this is probably an aquatic plant and then you can combine that with the fact that the sedimentology or the paleopodology, right, that the rocks are also saying, oh, this is a place with periodic ponding, or this is a place that has, you know, that's been inundated soil, then you can begin to, you know, combine these things, like looking at the landscape, like, okay, so this area was probably, you probably had standing water, there are plants that seem like they could be aquatic, combining all of these things, okay, this is probably aquatic, and obviously this is not something that you can do everywhere because you need to have multiple lines of evidence but it is a way of kind of like if you're not a hundred percent sure about one of the directions you're taking if the other road comes to the same conclusion you can be more confident that like okay this is these are probably some aquatic plants we talked about this in episode 231 which we keep referring back to about secondarily aquatic animals that when we're identifying them in fossils, sometimes you find a flipper and that's fantastic. Other times you have to go, okay, well, it was surrounded by fish. And that's a pretty good indicator that it was hanging out in a place that fish were. Look how dense these sloth bones are. Yes. It's got these dense bones. It's surrounded by fish. It's in limestone. Yes, exactly. It feels like with plants you could also infer if this is in an aquatic sediment, this is a river, a lake, or whatever it was, and we're finding parts of the whole plant. It's not that a piece fell in from the shore. The roots are in here. The stem is in here. This plant was growing in the water. And that is a very tricky thing because these sorts of, you know, water, you know, riparian or lacustrine or whatever, these like water associated environments, you will get leaf litter that will fall into that. And you can get a flooding event so that the leaves can be covered quickly. But that doesn't necessarily indicate that they're aquatic. They can be near water, right? you can have like a gallery forest so for us it's along the water so that's like so you have to be very very intentional like very specific like what did you find what do the rocks actually say and it's wild too because like so often in paleontology this is true in paleobotany and other parts of paleontology too is that we will let one of those lines of evidence like supersede what is very obvious like something that's very obvious like for example This is here. Ergo, it must be this sort of environment or ergo, it must be this time period, even if you have really concrete evidence to suggest that like, oh, no, I think we're right. Like, for example, my friend James, James Lambsdale. Paleo after dark. Shout out. It's true. Go check him out. He studies horseshoe crabs. And for a long time, people just assume that if you have a fossil horseshoe crab, that automatically means marine. So even if your sedimentology suggested it's freshwater, no, no, no, no, no. Horseshoe crab means marine. And then more research that he was involved with shows like, no, no, no. There were also freshwater horseshoe crabs. So maybe if the sedimentology said it was freshwater, that might have been right. Yeah, it's that danger of when you read something, they go, well, this group was blank. And you go, well, the ones we know of. Right. Right. Look at those dense bones on that sloth. Yep. Exactly. So, Allie, you mentioned that the earliest fossils of aquatic plants are Cretaceous. Yes. What are those like? What are those? What plants are those? So there are two in particular that I'm going to talk about. So there's, to me, as a paleobotanist, this is a very famous fossil. and I just realized that I'm going to tell you the name and neither one of you are going to recognize it, and so I'm accepting this fact. Arcade Fruits. That's the one! Is it? Nice. That's what I was expecting. I did it. I know a plant thing. Allie's been coming on the podcast for eight years, and some of it's starting to wear off. And you've listened to me and Nora talk about a lot of plants. I sure did. Wow Arcade Fructis, one of the prime candidates For the earliest known flowering plants Is an aquatic plant Obviously everyone knows that Will knew that Sure I am so accustomed I remember very vividly in the fern episode When I realized that Neither of you knew a single fern And so I've had to temper my expectations But apparently I went too far Oh, goodness gracious. Don't worry, we'll disappoint you next time. Listen, if you put the bar underground, you'll just surprise everybody. You're definitely not going to know the second one. So anyway, Archae Fructis, yes. That's the only fossil plant I know. That's not true. It's not true. I thought you other ones. Anyway, Archae Fructis was originally described as the oldest known angiosperm. So it was originally dated as late Jurassic from China. So more recent dating has adjusted that age to be closer to the mid-early Cretaceous, which is much more in line with other early angiosperms. So, like, still a really cool and impressive fossil, but not as much of a, like, oh, this is so much earlier than everybody else. so it's small it's herbaceous and it has multiple adaptations for aquatic life this is the thing where i was like oh my god this is so dense i don't know how to describe this to a non-botanist but for example it does have those like very strongly dissected leaves it had multiple very clearly aquatic adaptations so arcte fructus that is probably the most famous fossil aquatic plant to a certain type of paleontologist. There's another one that is really important to me that I'm not going to talk about just yet. But another really early aquatic plant is Monsequia. I have heard of that one. You have? Because you talked about it. I have? Probably. I know the name, so someone told it to me. It must have been me. It was either you or Wikipedia. It was probably Wikipedia. because I don't think I told you about this. So Monsequia is comparable in age. So it's from the Pyrenees of Spain. It's Bahramian in age. So it's the middle early Cretaceous, roughly 125 to 130 million years ago. So again, the same time thereabouts is Archae fructus. So it has been interpreted as a submerged aquatic plant, closely related to Ceratophilaceae. So that is a modern family that is aquatic, and it is like a prototypical submerged aquatic plant, right? It's really feathery looking. If you look up pictures of Seretophyllaceae plants, like, yep, that's what an aquatic plant looks like, a submerged aquatic plant looks like. So as I mentioned, it is contemporaneous with Archaephorctus, right? It's living around the same time. So these are two very early angiosperms, and they're both obviously aquatic, which indicates that the aquatic habit evolved very early. They began evolving because they did it like 200 and sometimes. They began evolving very early in the angiosperm lineage and therefore could have played a big role in their diversification. diversification. Like, that's the thing we talk about with flowering plants all the time, is that they were able to get in every sort of environment. And here's just another option that they're like, no one's living here. Dibs. Right? Yeah. Incredible. So the archaea fructose is maybe the only fossil aquatic plant that I know. Yeah. What other ones are there? What are some other fun examples? So I have talked about another one on the podcast. I talked briefly about azola, in the Azola event. Yes, in the ferns episode, 215. Yes, so this, very briefly, this was the Azola event was a bloom, well, bloom in terms of there were a lot of them, not in terms of flowering because they are not flowering plants, of the aquatic fern in the Arctic Ocean during the PETM. So this was when global temperatures were much higher and you could get aquatic ferns living in the Arctic, which is absolutely not something that is happening today yet. So weird. So another one that, again, so this is another plant that is very important and obvious, like was an obvious choice to me. But again, that is because I am in fact a paleobotamist. so have you heard of paranymphaia i have now that's what i figured okay i've heard of him because you mentioned nymphales before and i was like i've heard of that i don't know what it is but i know i know the name so nymphaia is the water lily oh well there you go that's why i've heard of it yes that is true that is why you heard of it so nymphaia is the water lily Paranymphaea, specifically Paranymphaea cracifolia. So this is a ancient water lily or water lily like thing. So it's an aquatic plant. It's similar to a water lily. That's why it is called Paranymphaea. And it is an indicator fossil for the early Paleocene. Oh. So if you have Paranymphaea, that is an indication that you were in the earliest paleocene not in the cretaceous yeah it shows up in the earth after the extinction event correct in like the first million years of the paleocene cool this is something that that we argue about a lot just like not me i don't work in the paleocene but paleobotanist basically it's like is it actually a paleocene indicator is like because You know, people will like, oh, I found it in the Cretaceous. And then there's a lot of back and forth of like, are you actually in the Cretaceous? Right. If you found it, then by definition, you didn't find it in the Cretaceous. Right. Because it's defined right. I had a friend who one time, the question came up of like, were there any dinosaurs that survived beyond the Cretaceous and into the Paleocene? And he said, no, because the Cretaceous is defined by the presence of dinosaurs. So if you find a dinosaur, it's the Cretaceous. Yep. That is logic. But so those are some other exciting examples because, honestly, like the fossil record of aquatic plants is, yeah, variable. We don't really have any aquatic bryophytes, you know, mosses and friends. And then we don't really have a record of anybody being aquatic until the Cretaceous. But in the Cretaceous, we also get things. A lot of these ancient aquatic plants, because we're in the Cretaceous, are actually assigned to modern genera. So you'll notice that a lot. So Archae Fructis and Monsequia are not, obviously. Well, I say obviously. I know those aren't modern genera. I think Archae Fructis is obvious that it's not a modern genus. Right. given the name but uh a lot of these are either assigned to modern genera or given names like para-nymphaia right that's like you know it's not nymphaia but it's close to nymphaia or like you know it's nymphaia adjacent and that makes it a little bit complicated to like look into this just because in general aquatic plants are not as well studied as terrestrial plants so we just generally know less about them. Their fossil record is a little bit, you know, a little bit worse. And so, yeah, there's a lot of gaps in knowledge of what are these things? Where are they found? We got to get a little bit creative with it. But aquatic plants are really cool. Like I had some in my dissertation. It was very fun because, too, it helps really, like in the study that I did, like give a clearer picture of a landscape, not just like it is a forest it's like no there's a forest but also like right there there was a pond 18 million years ago which is super fun the fact that plants are still like going into the water is really fun like i'm so here i'm so here for it you go you go aquatic plants so do we have much of an idea of how plants make the transition into the water do we have it sounds like we don't have a whole lot of fossil record but are there examples among modern plants or evidence among modern plants that gives us an idea of what that transition might look like not really not really okay because again part of the problem too i'm reading through my notes and realize that i set myself up for failure because my notes are looking are talking about algae because again we do know a lot about like how plants like you know went from being aquatic to going onto land we have a lot of evidence for that but there is less evidence for these like i guess the closest you get to transitional things uh the fossil record are going to be things like archa fructus and monsequia because they are very early on so there are some things it seems very likely that the way that plants made it into the water is by this like amphiphate route, right? By basically getting your feet wetter and wetter and wetter. Because as we mentioned at the very top of the episode, plants, you know, even terrestrial plants, like I am very much a land plant, can often survive some degree inundation, flooding. One of the papers I was reading where they were putting plants in water, like land plants in water and calculating their photosynthetic rates because they were because in order to compare how efficient and effective like submerged aquatic plants are versus like you know you know amphophyte you know can go either way sort of uh plants versus like i am a land plant and how well they could photosynthesize underwater unsurprisingly there is a little bit of difference between you know thoroughly land plants and like i could go either way sort of plants like you know the i could go either way sort of plants are gonna are do do better they are better at photosynthesizing literally underwater but aquatic plants are on another level which makes sense because like if you are going to fully commit to being fully submerged, that is, that can be a big level of commitment. It's like, especially again, with like the emergent aquatics, you kind of have best of both worlds versus like, you know, the plants that are living their entire life cycles submerged. That is a big difference. That is a big commitment, right? You know, the differences in the way that you're pollinating, in the way that you are acquiring carbon. I suspect that the way that this is going to happen is going to be the, you know, the pathway of I am a land plant. I'm a land plant that can, you know, get my feet wet. I am a land plant that is, you know, spends part of my lifetime submerged. I am a completely submerged aquatic plant. Right. Right. This is similar, again, to draw the comparison with animals, where even if we don't know the exact trajectory of a particular lineage, there's so much diversity in modern animals that we have representatives that represent basically every step along that hypothetical path. With living plants, you've got land plants that are adapted to dry habitats and wet habitats. You've got things like mangroves, which live in swamps. You've got those partly in, partly out. You have plants, based on your descriptions of aquatic plants, you have plants today that are literally half in and half out. Yes. Yes. Both temporally, right, that like part of their life cycle is in and part of it's out, and also plants that have in-air leaves above the water and underwater leaves below the surface. Yes. So we do seem to have, like you could take modern plant diversity and line up a bunch of examples to form a very cogent hypothetical evolutionary trajectory. Absolutely. And it does, it like makes a lot of intuitive sense. The thing that's just kind of wild about it is the fact that you have such a truncated timeline. We are only talking about like a hundred million years, give or take. Yeah. Which makes it sound like it's not all that hard for plants to do. They've done it hundreds of times. This is, okay. I know that I have an angiosperm bias, but there's a reason for that, because they're great. And the fact that it did not... Gymnosperms, what were you doing? You've only evolved this once. Get it together. Ferns, hundreds of millions of years. And it took you until the Cretaceous to try out... They're like, there's sharks in there. I mean, that's such a good point. I did it. I wasn't going to go in there until I knew it was made. I've seen that movie. And I saw a bunch of flowers who were dummies who went into the water, and I was like, oh, okay, same. Well, they can do it. Joke's on them. At least one shark eats grass. But that's the thing, right, is that, like, that's kind of the wild thing about this record, is when you have hundreds of millions of years of time, that is spread across the globe. You know what I mean? Like you have so many opportunities to find fossils from all of these places in all of these times. And sure, the fossil record isn't complete, but if you were dealing with more space and more time, you just statistically have more opportunities. But with aquatic plants, we are talking, you know, what, 130 million years? That's it. That is not a lot of time, and therefore it can't be as much space on Earth. And a lot of these environments aren't great for preservation or just the nature of these types of plants, right? Like Podostomaceae, super cool. Can't imagine has a particularly good fossil record. I mean, they are literally attached to rocks, so maybe that helps them. Right, but they're not woody plants. No. They've got very tiny leaves or very thin leaves. Yes, they tend to be very flexible. They tend to be very soft. Many of them are incredibly small. So, again, like all of these adaptations that are making it easier for them to live in these aquatic environments are ruining my life personally. for finding them in the fossil record. So one last question, and it's a question that I do like to ask Allie at the end of many of our plant episodes. How do aquatic plants change the world? Aquatic plants expanded and transformed terrestrial ecosystems. It gave, you know, there were already animals that were living in rivers, right? There were already animals that were living in wetlands. but plants are primary producers. There's already algae and things like that that are living in these environments, but by adding plants, specifically angiosperms, you are really upping that primary production. And they are, in fact, the basis of the food web for many wetland fauna, aquatic in general, but especially in wetlands. These aquatic plants are really important. And aquatic plants are very, the word that's coming to mind is chemically efficient, which I mean. So aquatic plants are very, very good at removing excess nitrogen and phosphorus from the water, which is really helpful for humans. So humans, we make like constructed wetlands or things like that are doing some sort of like remediation. Humans will plant like wetland plant use wetland plants as a pollution management tool so when you have like you know fertilizer runoff and that sort of stuff being able to absorb that uh you know having the plants uptake this nitrogen this phosphorus can prevent algal blooms because that can be very harmful right like that can mess things up and then similarly they have a really big impact on the soil chemistry of these sorts of like riparian, et cetera, environments. So in addition to taking up the nitrogen, the phosphorus, that sort of thing, their roots, their stems, their leaves, just the bodies of the plants in general, slow down the water, like the flow of the water and can capture sediment. So again, they're actually like affecting the structure of these environments. Yeah. The famous thing with mangroves making islands. Yes. Yes, exactly. And there are a lot of, okay, so in like Egypt and like that neck of the woods, like Sudan, there is a very particular type of environment that is associated with papyrus. Because there are these kind of like floating little islands, right, that will group together and you'll get this very particular sort of environment that's only found associated with papyrus. Another thing, seagrasses made a new biome. Yeah. Oh, sure. Uh-huh. So seagrass meadow is a biome. Mm-hmm. And it is super productive. Yeah. It's very productive. It's like a plant reef. Absolutely it is. So that is one of the things in my notes. The diversity of seagrass meadows is comparable to coral reefs. Whoa. Uh-huh. That's something I think it can be easy to forget, especially when we talk so much about like rainforests and these on land diverse biomes. But coral reef and rainforest are like the top two. Yes. Those are what you know on land. Those are your champions of biodiversity. Yes, exactly. But the seagrass meadows are up there. That's wild. Which is, yes, it is, especially considering that I did not realize how extensive these seagrass metals are, because that's the other thing, is they are way more widespread, I think. So, like, coral reefs, we associate that with warm water. You don't have coral reefs, you know, off the coast of, you know, England. Yeah. But you can have seagrass much further north, right, like in the temperate North Atlantic. Yeah, and reefs tend to only form in a very narrow band off the coast. Absolutely. It's a very specific region of the coast that they are ideal for. And seagrass meadows can cover acres and acres and acres in many – so you can get a much wider environment than a reef, which is very cool. Yeah, spatially, we're talking about a different scale. And they're excellent carbon sinks. Yeah. Yeah. I have a renewed appreciation for seagrass, which I'll be honest, I basically never thought about before this. It was on your list of the two aquatic plants that you knew. That's true. I knew two aquatic modern plants and one aquatic fossil plant. Yeah. Well, and it's so cool to mention that seagrasses are such a boisterous biome, because when you look at it, it looks very homogenous. Yes, it does. Right. Like a grassland. Yeah. Yeah. But more like a lawn. Yeah, exactly. Like, it's just the same, because there's not competing plants. It's not a whole bunch of, like, it is seagrass. and like reefs and rainforests when you look at them they look diverse and crazy so I think it's very easy to underestimate you look at that and you're like all right so it's like some manatees and some little fish and it's like yeah but you're also forgetting that this is covering a huge area so throughout it you can have a bunch of big animals all spread out and lots and lots of little animals within. Absolutely. And there are a lot of shocking number of species. There are multiple families of seagrasses. So like, you know, even though to us, and I am fully looping myself into this group, they look like that is grass. I mean, seagrass, you know, it looks all the same. Like it's super not. There are so many different species of this. And yeah, I think that's one of my big takeaways. Please respect the seagrass. Yeah. And they are environments that need protecting. Oh, they absolutely do need our help. They are getting devastated and they don't get talked about very often. This whole episode has just been like wetlands and swampland mangroves and all these places that I'm just like, ugh. These are places that are almost universally doing very poorly these days. Well, because a lot of the places that these plants grow, like shallow coastal areas, that's where we love to go boating and fishing and industrialize. Like, we love to use the same water that seagrasses love. Or to drain wetlands for agriculture or, you know, construction, that sort of thing. So, yeah, like that's the thing about all of these sorts of environments, all these sorts of these plants. So one of the things that I was looking through, so I was looking at by what percentage of them are threatened and endangered. And there are some groups of aquatic plants with, you know, smaller distributions, fewer number of species, that up to like 60 to 80 percent of the species are threatened and endangered. Yeah. In the river weeds, it was like 200 species are threatened or endangered. Because, again, they have these very narrow ranges. Frogs. Yes. Yeah. They have these very restricted ranges in places that we are messing up. Or we are changing, changing in ways that seem fine, but the plants are like, cool, that's the end of me. Guess I'll die. Yeah, guess I'll just die. Well, this has been a fascinating conversation about aquatic plants. as usual with our Allie episodes, a real overview, a real bird's eye view of this massive diversity of plants in this particular lifestyle. Before we wrap it up, Allie, we have a patron question. Every episode, before we wrap the whole episode up, we like to answer questions submitted by our patrons, and we get patron questions every now and then that are plant questions, and I hold on to them and then I inflict them upon Allie. Speaking of unique adaptations in plants, Travis's question states, I recently visited Sequoia National Park and have been wondering what kind of selective pressures would result in such marked gigantism in redwood trees. What niche do redwood trees fill in their environment and why don't other continents and environment have similarly huge trees. Excellent. All right. I had to work really hard not to get two in the weeds on this because it is only a brief question. I know. I can't. But this is what I got. So in general, conifers, so that's the group that includes sequoias and their friends, are uniquely adapted to be superlative. So they're very long-lived. They're fire adapted. plus the environment where the sequoias live is pretty much ideal, right? It's not too hot. It's not too cold. There's fog, which is good for water and cooling. There's abundant rainfall. There's rich soils. It's honestly the best place to be a plant outside of like a tropical rainforest. And honestly, that might be too hot for some plants. So in addition to that, redwoods can absorb the water from the fog through their leaves, which is not something that all plants can do. And they have these interconnected root systems with other trees so that they can share nutrients, but also like provide strength and support. So this is basically the perfect combination because of the adaptations of this group of plants combined with the environment that it's living in. Like that's what allows it to allow the group to get so big. They can basically grow all year round, which is, again, not something that they'd be able to do in necessarily different parts of the world. In terms of their niche, what part of the environment are they? All of it, kind of. Right, they are the environment. They are the environment. So they are the basis for the entire forest, right? So they are kind of a forest unto themselves. There are lots of plants and animals that live on top of these trees. Like, I've seen pictures of basically full trees living on branches of redwoods because they're just so big that they can. And people say Star Wars environments are unrealistic. I know, right? It's wild. I mean, they also filmed Star Wars in redwoods, so, like. Exactly, yeah. Yeah. Is this not just Indora Kashyyyk? I know, right? So, yeah, and not only that, but they allow for this dense understory because the water can drip from the canopy. So it's not getting stuck on there. They're still getting moisture down under there. They have this really rich soil. And a lot of trees can hollow out and still survive. So it's places for animals, other plants, et cetera, to live. They are kind of the environment. But to that last point, why don't other continents and environments have similarly huge trees? That is not true. So we have the tallest in North America, but it's like, yeah, pretty much everywhere has tall trees that are comparable. So of the top 10 record trees by species. So these are the tallest species. North America has one, three, four, six, and ten. Okay. Australia, excuse me, Asia has the second tallest tree and the fifth tallest tree. Australia has seven, eight, and nine. And so North America, Asia, and Australia, all of the top ten tallest trees come from those three places. Gotcha. So redwoods are perhaps the most famous. Correct. Especially if you live in North America. Correct. But of that list, the interesting thing, so of those top 10 species, half of them are gymnosperms and half of them are angiosperms. The tallest, like handful, are all gymnosperms. But the second tallest used to be an angiosperm, but then it was impacted by fires in Australia and lost several meters. So it's like it went down on the list. But the interesting thing, I know, the interesting thing is that all of these plants are living in similar types of environments. So it's a lot of these temperate rainforests. This is a really good place for these trees to live because they have these really long growing seasons. It's not too hot. They have a lot of water. it is kind of wild how similar like some of these are actually living in tropical areas which also great to be a plant but yeah this like similarity like general similarity of environments in like across you know across the world so as as much as redwoods are super cool big old stand for redwoods there are lots of other really big trees out there and i want to meet them Have not yet. Very cool. As is so often the case, the superlatives among plants and animals tend to be the right combination of environmental conditions and specific adaptations that allow them to achieve heights, figuratively and literally, that no other species are able to do. Absolutely. Thank you, Travis, for that question. And thank you, Allie, for that answer. That's the end of the episode. Listeners, be sure to hop over to the blog post where you will find links and pictures for more information. For those of you that want to do a deep dive into aquatic plants, thank you to all of the people who requested this topic. We always appreciate those requests guiding us to the next subject of our episodes. Thanks to all of our patrons for your incredible support on Patreon. A special extra special thanks to our top tier patrons, as always, Jeff Ellington, Danielle Loves Bugs, and Sarah May. By the time you're hearing this episode, we are just days away from celebrating the nine year anniversary of Common Descent. So stay tuned to check out. We'll probably be doing a live stream. We'll have some fun announcements of upcoming projects and things. Join us for that. And one last time, a huge thanks to Dr. Ali Baumgartner for coming back every few months to give us a bunch of plant stuff. Always a pleasure. We release episodes every fortnight. We release episodes with Ali every five months or so. So depending on why you listen to this, come back in one of those time frames for the next episode that will be of interest to you. sign off race okay bye thanks for listening to the common descent podcast you can follow us on facebook twitter youtube and check our wordpress blog for pictures and links after each episode huge thanks to our patrons whose support helps keep this podcast running and who get access to bonus goodies on Patreon. The song you're hearing is called On the Origin of Species by Protodome, which we found at ocremix.org. Thanks again for listening. We hope you'll join us next time.