The Evolution of Trees

Misha Glenny and guests discuss the earliest evidence we have of the existence of trees and how even plants we might have on windowsills or as vegetables in gardens can and do, in the right conditions, evolve into trees. Since their emergence around 400 million years ago after low lying plants started to develop stronger stems and grow taller and more upright, trees have transformed our planet, so creating ecosystems, altering the atmosphere and setting the stage for the world as we know it today. With Jenny McElwain 1711 Chair of Botany at Trinity College Dublin and Director of Trinity Botanic Gardens Christopher Berry Senior Lecturer in Earth and Environmental Sciences at Cardiff University And Bill Baker Senior Researcher at the Royal Botanic Gardens, Kew Produced by Conor Garrett Reading list: David Beerling: The Emerald Planet: How Plants Changed Earth's History (Oxford University Press, 2008) C. M. Berry, ‘Palaeobotany: The Rise of the Earth’s Early Forests’ (Current Biology 29, 2019) Christopher M. Berry and John E. A. Marshall, ‘Lycopsid forests in the early Late Devonian paleoequatorial zone of Svalbard’ (Geology 43:12, 2015) N. S. Davies, W. J. McMahon and C. M. Berry, ‘Earth’s earliest forest: fossilized trees and vegetation-induced sedimentary structures from the Middle Devonian (Eifelian) Hangman Sandstone Formation, Somerset and Devon, SW England’ (J. Geol. Soc. 181, 2024) P. Geisen and C. M. Berry, ‘Reconstruction and Growth of the Early Tree Calamophyton (Pseudosporochnales, Cladoxylopsida) Based on Exceptionally Complete Specimens from Lindlar, Germany (Mid-Devonian): Organic Connection of Calamophyton Branches and Duisbergia Trunks’ (International Journal of Plant Sciences 174 (4), 2013) A. Groover and Q. Cronk (eds), Comparative and Evolutionary Genomics of Angiosperm Trees: Plant Genetics and Genomics (Crops and Models, vol 21. Springer, 2017), especially ‘The Evolution of Angiosperm Trees: From Palaeobotany to Genomics’ by Q. C. B. Cronk and F. Forest Jennifer McElwain, Marlene Hill Donnelly, and Ian Glasspool, Tropical Arctic: Lost Plants, Future Climates, and the Discovery of Ancient Greenland (University of Chicago Press, 2021) Harriet Rix, The Genius of Trees: How Trees Mastered the Elements and Shaped the World (Vintage, 2026) W. E. Stein et al., ‘Mid-Devonian Archaeopteris roots signal revolutionary change in earliest fossil forests’ (Current biology, 30:3, 2020) pp.421-431 William E. Stein, Christopher Mark Berry, Linda VanAller Hernick and Frank Mannolini ‘Surprisingly complex community discovered in the mid-Devonian fossil forest at Gilboa’ (Nature 483, 7387, 2012) Max Telford, The Tree of Life: Solving Science's Greatest Puzzle (John Murray, 2026) K. J. Willis, J. C. McElwain, The Evolution of Plants (Oxford University Press, 2014) James Woodford, The Wollemi Pine: The Incredible Discovery of a Living Fossil from the Age of the Dinosaurs (The Text Publishing Company, 2005) Alexandre R. Zuntini et al, ‘Phylogenomics and the rise of the angiosperms’ (Nature vol. 629, April 2024) Spanning history, religion, culture, science and philosophy, In Our Time from BBC Radio 4 is essential listening for the intellectually curious. In each episode, host Misha Glenny and expert guests explore the characters, events and discoveries that have shaped our world.

• 0:00Speaker 00

  This BBC podcast is supported by ads outside the UK.

• 0:06Speaker 01

  We all have routines. I'm Jabraan and with diabetes, mine was finger sticks. Sometimes I skip them because it hurt. The Freestyle Libre 3 CGM changed that. It gives me glucose insights without finger sticks. Learn more at freestylelibre.us.

• 0:21Speaker 02

  Finger sticks are required if your glucose alarms or readings do not match symptoms or when you see check blood glucose symbol for the first 12 hours. The views expressed should not be used for medical diagnosis or treatment as a substitute for professional medical advice. Individual circumstances may vary. For prescription only. Safety info found at freestylelibre.us.

• 0:36Speaker 03

  Hey, I'm Niall Rogers. This fall, I'll be driving across the country, meeting some of today's coolest and most fascinating artists. We'll explore the stories before the moments that changed everything. Because every musician remembers the moment where it all began. Experience Before the Moment, a Lincoln original series on the iHeart Radio app, YouTube, or wherever you get your podcasts.

• 1:08Speaker 04

  OnDeck is built to back small businesses like yours. Whether you're buying equipment, expanding your team, or bridging cash flow gaps, OnDeck's loans up to $400,000 make it happen fast. Rated A plus by the Better Business Bureau and earning thousands of five-star Trust Pilot reviews, OnDeck delivers funding you can count on. Apply in minutes at ondeck.com. Depending on certain loan attributes, your business loan may be issued by OnDeck or Celtic Bank. OnDeck does not lend in North Dakota. All loans and amounts subject to lender approval.

• 1:38Speaker 05

  This is In Our Time from BBC Radio 4, and this is one of more than a thousand episodes you can find in the In Our Time archive. A reading list for this edition can be found in the episode description wherever you're listening. I hope you enjoy the program. Hello. We might take them for granted in parks, in our streets and in forests, yet trees play a crucial role in regulating our climate and providing the air we breathe. We build with them, rely on them for food and shelter, use them for paper, clothing, medicine and energy. But trees aren't simply a backdrop to human life.

• 2:19Speaker 05

  They're the product of a deep evolutionary history that transformed our planet. When they first appeared, they reshaped our ecosystems, altered the atmosphere and created entirely new environments on land. Well, with me to discuss the evolution of trees are Jenny McElwain, the 1711 Chair of Botany at Trinity College Dublin and Director of Trinity Botanic Gardens, Christopher Berry, Senior Lecturer in Earth and Environmental Sciences at Cardiff University, and Bill Baker, Senior Researcher at the Royal Botanic Gardens in Kew. Welcome to In Our Time. And Jenny, let me start with you.

• 3:01Speaker 05

  I think, like most of the listeners, I can say that I recognise a tree when I see one. But what is a tree?

• 3:09Speaker 06

  Yeah, that's actually such a hard question, because we have to define a tree without using the word 'tree'. So there is actually, there's a lot of arguments and discussion among plant scientists about what a tree is, but what we can say is that it has to have a trunk, so a main stem, and it has to have a canopy. And the canopy, we think, usually has leaves today, but not necessarily, so it is a canopy of branches. That trunk has to not die back, so we have structures that look like trees, but they're actually flowers.

• 3:44Speaker 05

  What do we mean by 'die back' exactly?

• 3:46Speaker 06

  So it means that it's a perennial structure, so that it will last for many, many years and not just die after one or two years. And then, to be a tree, the trunk and the crown have to be self-supporting. So what that means is that this beautiful organism can't rely on leaning on a wall, or before walls, leaning on another tree, or leaning on other vegetation. And then other people use a definition of a particular height and a particular width. So there's loads of arguments about that, but I, I think a good definition is a tree has to be above three metres. And then if you took your hand and at chest height measured the, the width of the trunk,

• 4:29Speaker 06

  it has to be wider than your hand to classify as a tree. And, and then the big controversy comes with wood.

• 4:36Speaker 05

  Yes, tell us, tell us, what is wood exactly? And can you have trees without wood?

• 4:42Speaker 06

  Yes, we absolutely can have trees without wood. Some botanists are really strict and they say you can't be a tree unless you have wood, but I, I, I think that's far too strict. And if you think of a tree, it can be woodless, it can have wood. Trees have worked out many ways of becoming a tree. So what is wood? Wood is a tissue made up of lots of cells and those cells are really complex and they are hollowed out and they really look like straws in their simplest form. And so they have a hollow centre and then the cell wall of the straw is thickened with a polymer that is called lignin. And lignin enables that tree to self-support and not fall down and not rely on other structures

• 5:26Speaker 06

  to, to lean on. So if the tree has lignin, we call it wood. Actually, the Greek for wood is called xylem and that's what those cells are called, wood cells are called xylem.

• 5:38Speaker 05

  And before trees came along, what was happening with plants on earth?

• 5:43Speaker 06

  Yeah, so we, we kind of always think trees are ubiquitous today, so we kind of think they've always been here. But if you look deep into evolutionary time using fossil plants, between about 460 million years ago and 390 million years ago, the world was treeless. And in actual fact, plants are just coming onto the earth's surface out of water and photosynthesising, so they're green. So if you could imagine, you would be walking in a world where you'd see lots of bare rock, very little soil, and the plants are leafless, they are rootless and there are no trees. So the, the, the highest plants are kind of brushing your ankle, touching your knee,

• 6:26Speaker 06

  but there's no massive tree structures on the earth before the advent of trees.

• 6:30Speaker 05

  So if they're, if they're rootless, that means they're sort of like mosses or so, or something like that.

• 6:36Speaker 06

  Yeah, that's right. So. Evolutionary groups that have evolved in the earliest phase of the Earth are mosses, liverworts, there's also ferns. So these plants all reproduce by spores. In the early record, they're rootless, but they evolve roots. And in their early record, they have no leaves, but they evolve leaves.

• 6:55Speaker 05

  Okay, so Chris Berry, when did the first trees then arrive presumably out of this vegetation? And what did they look like?

• 7:05Speaker 07

  So the oldest trees I've seen are about 393 million years old, from the beginning of the Middle Devonian period. And I suspect that a few million years before that, there's other types of simple tree leading up to these first trees that we know about. And the first tree we have is a cladozoalopsid tree, and it's called Calamophyton, and it's an extinct type of organism, so you wait.

• 7:30Speaker 05

  Just the definition of those two words.

• 7:33Speaker 07

  Cladozoalopsid simply means that the wood is branched. So inside the tree, there's lots of sort of network of wood, rather than a solid cylinder of wood that you might expect in an oak tree or something today.

• 7:46Speaker 05

  Got it.

• 7:46Speaker 07

  And the name of the tree is Calamophyton. So that's a strange word, which is, I think, a combination of a Greek word for reed and phyt, which means plant. It was considered very simple when they first found small parts of it.

• 8:01Speaker 05

  So these are the first trees that we know of?

• 8:03Speaker 07

  Yes, they are. Now that we've been able to assemble the different bits that we've known about into one organism, which is a tree. So it's a tree called Calamphyton. It's probably about two metres tall, consists of a trunk, it has simple but many roots at the bottom. And from the sides, and particularly the top of the growing apex of the tree, would be lots of branches. Those branches look a bit like, I'd say, maybe monkey arms with very long fingers. And attached to those fingers would be tiny little twiggy things, which weren't leaves, but were probably photosynthesising. And this thing would have just grown upwards

• 8:45Speaker 07

  to probably about maybe two and a half metres. So Jenny wouldn't call it a tree, which is fine by me, actually. But.

• 8:53Speaker 05

  Would you call it a tree then?

• 8:54Speaker 07

  Um, in its time, it was a tree, but we might not call it a tree now. It was definitely something that we'd look up to if we were a small arthropod crawling around on the ground back in the Middle Devonian.

• 9:07Speaker 05

  So Jenny, not a tree?

• 9:09Speaker 06

  I would call it a tree. I, I have a broad definition of a tree. I just gave the strict one.

• 9:14Speaker 05

  Okay, so we know about this because of the, the fossil record. Uh, sticking with that, Chris, what do those fossil records tell us about the first forests?

• 9:25Speaker 07

  Uh, the first forests I look at as occurring over the next period of about ten million years. So we find probably four really good examples of what these very primitive forests were like. If we look at the first one that was known about, the famous Gilboa fossil forest in upstate New York, um, we find these cladeosalopsid trees like calamophytum, except by ten million years later, they're actually about a metre in diameter at the base, maybe ten, twelve metres tall. So really substantial trees. Yep, we find in the sandstone quarry in upstate New York where this forest occurs, between, meandering between those tree bases, we find a woody trunk, but which is lying

• 10:09Speaker 07

  along the ground. It's a new type of plant called a, a neurophyte, very simple leaf-like twigs, again, on little branches. If we go back maybe two million years before that, go down the hills, out of the Catskill Mountains, down into the Hudson Valley, there's another place called Carrow, and there's another sandstone quarry there. On the base of that quarry, there are huge, great rooting systems, and that is the base of another woody tree, but this type of tree has learnt to grow upright.

• 10:42Speaker 05

  And you've been to the four major sites of the earliest fossilized trees that we know. Where are the other two?

• 10:52Speaker 07

  The other one, which is of a similar age to the two I've just described, is in Spitsbergen, about nearly eighty degrees north, though when that forest was alive, it was on the equator. And there we see lycopod trees growing, which is a third type of tree. And that tree has a little bulbous base and then a trunk, which is just a column, which would have been covered in little leaves. And when it got to a certain height, about three metres, it would then branch, start dividing into two and two and two and two and form probably an upright crown at the top of it. These trees are still extant today in the form of little herbaceous plants.

• 11:31Speaker 07

  And then the last and the oldest fossil forest was found by a couple of Cambridge sedimentologists, Neil Davis and Will McMahon, down on the coast of Somerset. And they sent me some pictures of some trees and they look a bit like a tire mark from a bicycle going across the sandstone. And I recognised immediately the pattern of branches that are found in Calamophyton, which is the oldest tree. It's from about 390 million years.

• 12:00Speaker 05

  Thanks very much, Chris. Bill Baker, from physical trees, early physical trees to trees as a metaphor. You've called the tree of life biology's periodic table. Can you explain what you mean by that?

• 12:16Speaker 03

  Well, metaphorical, the idea of the metaphorical tree of life has been around for thousands of years in religious, mythological, cultural contexts. Think of the tree of life in the Garden of Eden or this great tree, Yggdrasil, that connected the nine realms of Norse mythology. But what I'm talking about today is the evolutionary tree of life. So the genealogy of everything that lives and has lived. And I liken it to the periodic table because the tree of life helps us understand the properties of living things, just like the periodic table

• 13:00Speaker 03

  helps us understand the relationships and properties of the chemical elements. So if you are looking to find your way through the complexity of biodiversity.

• 13:13Speaker 03

  The Tree of Life is like a roadmap. It kind of cuts your workload down because you know you don't have to. If you're interested, for example, in a group of plants that might produce chemicals that could have medicinal value and you want to explore those plants for their medicinal properties, you don't have to look at every plant. You can use the Tree of Life and what we call its predictive power to direct your next sampling foray. So it's really central. It's the foundation of biology in many respects and indeed the kinds of things that Jenny and Chris have been talking about are all underpinned by concepts of the Tree of Life.

• 13:50Speaker 05

  And you've been involved in the building of a complex Tree of Life at Kew. Can you explain to us how you go about doing that? And what does it tell us specifically about the evolution of trees?

• 14:03Speaker 03

  In a perfect world, we'd be able to reconstruct the Tree of Life from what we see written in the rocks. The fossil record would tell us how everything is connected. But as Chris has just described very clearly, actually, the fossil record is very incomplete and it's difficult to piece together. But there is another kind of fossil record. There's the molecular fossil record, which is effectively the changes in DNA that accumulate over time. All of us, our cells have DNA. That is what encodes our properties and functions. And over time, DNA mutates. Now, if you can pull together DNA code, DNA sequence, as we call

• 14:46Speaker 03

  it, from different species but for the same parts of the genome and line those up, you're able to run it through a complex algorithm and infer a tree or recover a tree. We often talk about recovering as if it's a form of excavation, almost. We know that there is a tree out there, but that we have to somehow get to it through our molecular genetic shenanigans. I mean, building the Tree of Life is a huge global endeavour. There are many, many researchers involved in this. And at Kew, it's been our bread and butter for decades. For the last decade, I've led a programme called The Plant and Fungal Trees Programme at Kew, and we have recently, it sounds rather

• 15:27Speaker 03

  glib, we have recently completed the flowering plant tree of life, by which I mean we have sequenced one representative of every genus of flowering plant. Now, the flowering plants make up ninety percent of the plants that grow on earth today. Chris has not talked about flowering plants yet, he's talked about things that come long before flowering plants, but there are three hundred and fifty thousand of them. We've sequenced about ninety percent of the genera, that represents about ninety-eight percent of the total diversity, and we've done that using Kew's amazing collections and really novel genomic methods. And I think the thing we're most proud about is that everything that we have done is in the public domain and free for other people to use, and it's been a really wonderful

• 16:12Speaker 03

  springboard for other people's research.

• 16:14Speaker 05

  And are trees included in that? Because some of them are flowering and some of them aren't.

• 16:18Speaker 03

  Yes, so there are many tens of thousands of the three hundred and fifty thousand species of flowering plants, our trees. And what our Angiosperm tree of life shows us is that...

• 16:31Speaker 05

  Angiosperm?

• 16:32Speaker 03

  Sorry, flowering plant. Angiosperm is a synonym for flowering plants, plants that produce flowers and produce true fruit. And so our flowering plant tree of life shows us very clearly that trees are not a group, that they have originated repeatedly across this enormous group. We see a wonderful pattern in the way the flowering plants diversified. Very early on in their origin, about hundred and fifty million years ago, there was this enormous surge in diversification, all the major lineages, what we call the orders of flowering plants, appearing. But we don't think that they were trees at that time. The first groups that popped off were flimsy shrubs and climbers, or the water lilies,

• 17:17Speaker 03

  for example, they can't even make wood in their aquatics. There's a lack of clarity about exactly what the sequence was of diversification, but we know that trees were probably not there in the earlier stages, but by the end of the Cretaceous, they were very, very much present.

• 17:33Speaker 05

  Okay, so as we've established, they've arrived around three hundred and eighty, three hundred and ninety million years ago. Jenny McElwain, how did they start to change the environment?

• 17:46Speaker 06

  Yeah, so I think we mostly think of trees, we use the term ecosystem engineer. So they just build this structural complexity. So if you imagine you've got twenty herbs, you know, they're not trees, they're small in a space, and now swap that with twenty trees. So the trees will increase the volume of complexity. So as soon as you have trees, you begin to have layers of habitats. So let's say you go hiking on a hot day. It's really hot, it's really drying, but you walk into a cool forest, you can feel the moisture increase, you can feel the shade and the cool.

• 18:27Speaker 06

  So what trees do in a space is they create a microclimus. They change the light, so you now have understory plants, you have middle story plants, and you have canopy plants. They change the humidity, they change the complexity of how everything interacts. And this is just above ground, below ground, they're doing the same. So they're extracting elements from rocks, building soil, building relationships with fungi. So per unit space, trees add complexity, and they engineer space and climus and resources for other plants to come in and other animals and fungi, other groups to come in.

• 19:09Speaker 05

  So very fundamental, really, in terms of how life evolves.

• 19:35Speaker 01

  Driving across the country, dropping in on some of the coolest, most fascinating artists working today. We'll go deep into their lives and careers and hear what it was like before the moment that made them. From hitmakers like Miguel. That last year, finishing that record was the hardest experience of my life. Regardless of how everyone else buys into this, I believe in this and I'm gonna push. To rising stars like Alex Warren. You know, a song is a story and the verse is setting the scene. And for me at least, it's allowing me to be personal and vulnerable with the audience, whether it's about my wife and I'm being vulnerable about her, or it's about, you know, my parents and I'm being vulnerable to them.

• 20:18Speaker 01

  And it's almost like a cinematic piece in a way where each song tells that beautiful story. It's gonna be one hell of a trip. Experience Before the Moment, a Lincoln original series on the iHeartRadio app, YouTube, or wherever you get your podcasts. This is Jason Timp from Hoops Tonight with Jason Timp. Buy smart, drive for less and trade for more. That's Toyota affordability. And it starts with a great deal on an off-road ready Tacoma or half-ton Tundra. Two of Toyota's longest-lasting trucks, combining power for work, tech for adventures, and style in between. Built on a reputation for quality and reliability, Toyota trucks are known for holding their value, which can mean big savings when it's time for your next Toyota.

• 21:01Speaker 01

  So get a great deal today and great value tomorrow. Shop toyota.com for more.

• 21:06Speaker 05

  Toyota, let's go places. OnDeck is built to back small businesses like yours. Whether you're buying equipment, expanding your team, or bridging cash flow gaps, OnDeck's loans up to $400,000 help make it happen fast. Rated A+ by the Better Business Bureau and earning thousands of five-star TrustPilot reviews, OnDeck delivers funding you can count on. Apply in minutes at ondeck.com. Depending on certain loan attributes, your business loan may be issued by OnDeck or Celtic Bank. OnDeck does not lend in North Dakota. All loans and amounts subject to lender approval. Hello, Misha Glennie here. Did you know you can get episodes of In Our Time 28 days early with a subscription to the BBC website and app? Just head to bbc.com/subscribe to find out more.

• 21:54Speaker 05

  Chris, are trees from 390 million years ago recognisable to us? Or are today's trees very, very different from what first emerged? And if so, where do those differences lie?

• 22:08Speaker 07

  So if we look at the archaeopterys tree, the one with the big roots that we saw at Karo in the forest, this would be a recognisable form to us because it's got big sturdy roots, it's got a woody trunk with some sort of bark on the outside of it. It may have branches, but it definitely has leafy frond-like branches attached to it. So it would have nice green leaves and so it probably reached a height of maybe at that time 20 metres or so.

• 22:36Speaker 05

  So does it look like something like a pine tree?

• 22:39Speaker 07

  Yes, to a certain extent. That would be the basic thing that you might recognise, a sort of leafy pine tree, if you could imagine such a thing. The lycopods, such as we saw in Spitsbergen, were quite different, I think, to anything that we really see today because they would grow up as a leafy trunk from the ground. And they would grow up to, at this time, three metres maybe, and then start branching and have this branching crown of leafy, smaller branches at the top, which would then terminate in a cone, that would be where the reproductive part was. And I don't really know of anything that looks particularly like that today. There's some cactuses and things which maybe do a little, something a little bit similar.

• 23:25Speaker 07

  But the cladosealopsids are really fairly unique because the way that they support themselves is with this very much divided woody structure around a hollow interior. It's a bit like the Eiffel Tower inside the plant, holding it up. And then with these monkey-armed branches on the side of them, which then dropping off as the apex grows upwards. It's a form that we might recognise from a palm, I'm sure Bill might talk about this, or a tree fern, but without actually having any leaves. So a quite unusual type of structure, but quite distinctive.

• 24:02Speaker 05

  Like oaks and ashes and birches that we know today, when did they start evolving or do we not know?

• 24:08Speaker 07

  This will not be till probably about two hundred, two hundred and fifty million years later. So these early Devonian forests are really quite distinct. And one thing you should perhaps recognise is that there's no seeds there, there's no flowers. There's almost no insects, maybe just millipedes, no birds, very low diversity. Not this tropical ecosystem that we think of today as being a tropical forest. This is really something very distinctive and without the level of interactions that Jenny's talked about. Perhaps apart from the fungi in the soil, which might be quite interesting.

• 24:44Speaker 05

  Well, you mentioned tropical forests, rainforests. Bill, you've done quite a lot of work on palms. What can you tell us about palms and rainforests?

• 24:56Speaker 03

  Rainforests obviously are iconic places for trees. They're also really important for biodiversity. We think maybe half of all plant species occur in rainforests, which take up just seven percent of the world's land surface area. So they're really important. And that idea begs the question, well, how on earth did that come about? So the palms are fruitful, provide a fruitful line of inquiry on this subject. Because palms are found all over the tropics, they're widespread, two and a half thousand species. But they are mechanically kind of bound to the tropics. They can't cope with freezing on the whole, there are a few exceptions, don't write in.

• 25:39Speaker 03

  On the whole, palms can't cope with freezing because freezing causes catastrophic embolism of their plumbing. Basically, you get a bubble and it can't function anymore. So this makes them what we call niche conserved. They are bound to a certain environment. And as you can tell already, I love building the tree of life and my early days were spent frenetically building a palm tree of life. And we have used that tree to try to see what that might tell us about the rainforest. By combining it with fossils to turn this branching. Diagram actually into a proper chronology, if you like, so that the individual splits in this

• 26:18Speaker 03

  tree fit to a time. We've related on to that tree, the environments in which the modern species occur and reconstructed what the original, the ancestral condition might be. And that tree told us, that analysis published in 2011, told us that palms appear to have evolved in the rainforest 100 million years ago, somewhere in the northern hemisphere. This caused a bit of a drama because, in fact, from a paleo perspective, the fossil evidence for rainforest doesn't exist at that time. The earliest fossil assemblages that look like they characterize a rainforest don't come till after the meteor impact and the extinction of dinosaurs around 60,

• 27:02Speaker 03

  65 million years ago.

• 27:04Speaker 05

  So what's happening there if, if the evidence is so contradictory?

• 27:09Speaker 03

  Well, we, of course, what is science for if not for revisiting later? So the update to all of this is that we have managed to build an even bigger tree of life for palms with 80% of the two and a half thousand species in it now, that gives us a more nuanced insight that shows us that palms are even older, perhaps 120 million years, but that it appears now that they evolved in a non-rainforest environment, but quickly moved into them around 60 million years. So by doing more work, we finally get a close match that I hope will cause less controversy among my paleo friends.

• 27:46Speaker 05

  Thanks for that clarification, Bill. Jenny, we heard from Bill that palms exist in rainforests, or I think it was you, that they can't exist in different temperatures. So what makes some trees resilient and other trees not resilient?

• 28:04Speaker 06

  Yeah, that's, that's such a great question. And I actually think nobody can answer it, yes. So I think this is really an active area of research for plant scientists in all disciplines. And we really need to know which trees are going to be resilient in the face of climate change in the future. And there's lots of ways of answering those questions. You can come from lots of different disciplines and answer it in different ways. But I suppose, thinking of my own research area, we know from looking back at the fossil record, at times of natural global warming in the past, so this would be caused by volcanism. That if you push the climate too far and too warm, we know that trees have limits.

• 28:49Speaker 06

  So you push the climate beyond their niche or their adapted envelope. And they suddenly disappear. And we don't see them as fossils anymore. And instead, we see the really ancient plants thrive, like ferns and those mosses that we talked about in the early phase of the earth. So what we do know is that trees, all trees have limits. And we see this if you go to the Arctic today or the Antarctic, there are no trees. It's a treeless landscape. It's because it's too cold. And then you see it in a desert. In the most extreme deserts, it's too hot. So I kind of think we can't be complacent. We know trees, we love trees, but we absolutely can't be complacent.

• 29:34Speaker 06

  And we've set up a project in Trinity College Botanic Garden called the Witness Tree Project. And the idea is that all trees are sensors and they're witnesses of climate change. And because they're long-lived organisms, you know, many live for thousands of years, most live for hundreds of years or certainly decades. And we are tracking 21 trees, and it was very difficult to choose which ones. 21 trees every year over time to answer the question you posed, which trees are most resilient? And we're trying to understand, it's called a common garden experiment, because we have trees from all over the world, growing in the same botanic garden.

• 30:19Speaker 06

  So we have trees from the subtropics, trees from cold environments, trees from very warm environments. And we're trying to understand fundamentally, what is it about their traits that enable some to be resilient and others to not withstand the changing climate?

• 30:37Speaker 05

  So Chris Berry, in that case, presumably even resilient trees would find it difficult to adapt year on year. So you're looking at tree resilience over millions of years, hundreds of millions of years. Do you, are you able to say, ah, yes, this tree faded away but became an oak tree or something like that? Or do you see hard cutoff points?

• 31:07Speaker 07

  One of the interesting things about how trees grows is where the growth occurs, where the primary growth occurs. And for my very old trees, this tends to be at the actual apex of the trunk. So at the apex of the trunk, there's a thing called a meristem, which is producing new cells which become part of the trunk. And in these ancient types of trees, then pretty much the whole body plan of the tree was organised from there. So it would be given instructions as to where the branches would grow, when they grow in geometric patterns, coming back from the area. Meristem. Problem with this is that that's extremely vulnerable, because if you take out the meristem, if you have frost or something, or this big bulbous

• 31:50Speaker 07

  thing on the top of the trunk, then it can easily be destroyed. And the same for the lycopod trees as well. I think archaeopterys, the big, tall, woody tree that we see at Caro in upstate New York, is a really interesting thing, because with my PhD student Amy Wyatt, we've been in Spitsberg and collecting what we think are trunks of these archaeopterys trees. And up to a certain size, they seem to have every geometric insertion of the leafy branches that they had, which seems to fit in with this model. It's all coming from the apex. But work by American, particularly French colleagues, looking at the anatomy of some of these trees, shows that

• 32:31Speaker 07

  there's a new type of branching which can develop in archaeopterys. And that's to say that it starts growing new branches from essentially the surface of the wood. So it can produce a new branch anywhere on the trunk. And that can grow into a big branch, a long-lived branch with fronds on it itself, or even into a new trunk. So that sort of development gives the plant much more resilience, because you can lop off the top, you can have wind damage, other sorts of damage. Another tree can fall down and take half of it away, it could still grow. So I think basically, within archaeopterys, at some point, it changed from one type of

• 33:13Speaker 07

  branching to the other and became more resilient and lasted for 25 million years as a genus. And I think you can also add seeds to that. If you add seeds to a plant, then it's also going to become more resilient.

• 33:27Speaker 05

  When do seeds come in, as it were, for trees?

• 33:30Speaker 07

  For the trees, not totally sure, but trees, seeds appear in the fossil record towards the end of the Devonian, but within shrubby plants rather than within trees. So the first seeds are probably in plants which will later become trees rather than in the earliest trees.

• 33:48Speaker 05

  Bill, why does so many plants end up looking like trees? Is there something about the tree's structure which makes it particularly efficient or adaptable?

• 34:02Speaker 03

  Well, being a tree has a lot of benefits. It gives you more access to light, probably more photosynthetic efficiency, it gives you longevity, perhaps makes it easier for you to disperse your pollen or seeds. And because these pressures exist in many different places, this leads to what we call convergent evolution, the independent origination of traits in unrelated lineages. I mean, there is of course selection to not be a tree in some places. There are no trees up beyond the tree line in the mountains because it's actually better to be able to die back to a perennial root stock.

• 34:45Speaker 03

  And in the desert, it's better to be an annual and, you know, live fast, die young in an environment where there is not much water. But as a result, we see in the flowering plants, at least, we see many instances of plant families that have both tree and non-tree members. So, you know, we all know the apple, cherry, plum, for example, they're all members of the rosaceae, the rose family, but so is the strawberry. And everyone knows that strawberries don't grow on trees. The same with mint, for example. One of the relatives of mint, our little sappy herb, is the great teak tree, one of the most valuable timbers on the planet.

• 35:30Speaker 03

  And palms really take the biscuit because they can't make proper wood. They grow a bit like Chris was describing earlier from a big fat bud on the top.

• 35:41Speaker 03

  They are embedded in the monocots, which is a group that includes cereals, rice, as well as orchids, lilies, normally floppy things, sappy, things that can't make proper wood, and yet palms have escaped this constraint to produce trees that can be as tall as sixty metres. And in the Amazon, six of the ten commonest trees are palms. So that means the commonest tree and one of the Asai species, euterpi precatoria, there are five billion individuals of that, of that thing, which is kind of just pretending to be a proper tree.

• 36:19Speaker 05

  Jenny, I want to concentrate a bit on what the evolution of trees can tell us about the environment. Presumably before trees came along, the earth was still pretty hot and humid, I would have thought. What do trees do to change the environment?

• 36:37Speaker 06

  Yeah, so we can, trees are our sensors of their environment, so we can actually use them in the fossil record, because we have beautiful fossils like that Chris has spoken about, we have fossil leaves, we can use those fossils of trees through time to reconstruct how the environment has changed. So we've been able to reconstruct how the atmosphere has changed in terms of how much carbon dioxide there was in the past, how much oxygen there was in the past. And also then if you've got greenhouse gases, you can plug that into a climate model, work with your climate colleagues, and you can reconstruct how climate has changed through time.

• 37:17Speaker 05

  So when trees first start appearing, do they begin to oxygenate the atmosphere?

• 37:23Speaker 06

  Yeah, so I think that there's a long transition, but the net effect of going from a treeless world to a world of forests and woody organisms and trees is that those trees sequestered, so they pulled carbon out of the atmosphere. And then many of them, like the lycopods that Chris was talking about, were Rather than fungi breaking those trunks down and releasing the carbon back, that carbon was trapped in swamps and peats. And the Ness effect, over time, millions of years, is that carbon dioxide levels dropped from really high levels, really hot earth, to a cool climate.

• 38:08Speaker 06

  And oxygen levels were increased. So about 300 million years ago, we had this peak in oxygen. It could have been higher than 25% oxygen, even 30% oxygen, so much higher than today.

• 38:21Speaker 05

  So does that mean that the methane, for example, that's being released from from peat boggs and from permafrost and so on as the as the earth warms? Is that are those gases which trees originally stored?

• 38:39Speaker 06

  So partly, I think, any of the carbon in our fossil fuels, so coal, oil, is the remnant of photosynthesis from millions of years ago. Yeah, so we're burning thing carbon that was stored millions of years ago and took millions of years to store, and we're releasing it rapidly into the atmosphere.

• 39:02Speaker 05

  In a very short space of time, obviously. Chris, as well as cooling the planet, trees also contributed to warming the planet? Is that right?

• 39:14Speaker 07

  That's right. I mean, I'm massively impressed by how much carbon can be sucked out the atmosphere by trees. It's amazing. If we look at the NOAA graphs of carbon dioxide changing over the year, in the northern hemisphere, summer, we can pull out 1% of the carbon dioxide in the atmosphere in one year. It then gets released back again as the leaves sort of decay. But so over millions of years, this has got to be a really serious thing. So you can model that, as Jenny says. And one interesting thing that I think, out of all the papers I've read, I've been down to South Africa, which was about 70 degrees south, back in the late Devonian, and there's archaeopterys trees there.

• 39:56Speaker 07

  And that's 70, that's more near the pole than Reykjavik. You know, why were there in the late Devonian trees there? Because Jenny said that all this carbon dioxide's been pulled out of the atmosphere. You'd expect that the planet would just get cooler and cooler and cooler. But the models of my French colleagues actually suggest that temperatures stayed the same as all this carbon dioxide get pulled out in the atmosphere. And in their model, which is a conceptual model, it's not real life. In their model, the growth and spread of the forests changes the way in which the earth reflects sunlight. So instead of the sunlight bouncing off bare rock and so on, and back into the atmosphere,

• 40:39Speaker 07

  back into the space, that heat comes in, it hits the plants. As you know, tropical forests are very warm, it absorbs heat and moisture and all the things that we've talked about. And so the reverse effect of the forest spreading actually delayed the cooling of the planet. And it wasn't till the very end of the Devonian that it sort of caught up. And then we descend into an ice age in the early Carboniferous.

• 41:03Speaker 05

  Bill Baker, we've heard how ancient trees evolved over millions of years. Are trees still evolving now and do we know how they're evolving?

• 41:16Speaker 03

  Yeah, absolutely, they are. It's a bit hard for us to see on our kind of human timescales, but on evolutionary timescales, we know that there's still a lot going on. So for example, we know that some groups are radiating really rapidly. The Inga trees, for example, in the Amazon, really important trees to people and to the forest. The Inga trees have produced 300 species in the last 10 million years, which is an astonishing rate of diversification. We also know from islands, from weird things that happen on islands, that trees are evolving. Islands, there's a thing called island syndrome, where you get, for example, gigantism.

• 41:59Speaker 03

  Think of a giant tortoise on the Galapagos or flightlessness in birds like the dodo, the now extinct dodo. Well, in plants, we get what we call insular woodiness. Um, which is when formerly herbaceous lineages become woody, not necessarily trees, but they become woody. So for example, in the Canary Islands, there are forty, forty-one independent lineages that have done that. Um, so you get sort of thistles that are now quite, you know, well, they're stumpy trees. My favorite is one that I've, I've been lucky enough to see on, on Lord Howe Island, which is a little flake of a remnant

• 42:38Speaker 03

  volcano, um, two hours flight east of Sydney. Uh, and there you can find a relative of the, of the African violet, which many listeners will grow on their windowsill, little mushy house plant, but it's, it's, it's, it's a great big tree. Um, and, uh, it's, it's a bizarre experience as a botanist to see something you really associate, uh, with the, with the forest understory there, um, with its sort of spectacular waxy orange flowers. They call it the pumpkin tree, I, I think because of the, the color of the flowers.

• 43:12Speaker 05

  Uh, and which one of you spoke about cabbages which might be turning into trees?

• 43:17Speaker 03

  Yes, that's the case. It's that, yeah, that's, that's the case.

• 43:19Speaker 05

  What is a wooden cabbage? Tell me.

• 43:23Speaker 03

  Um, not, not especially handsome, but, uh, nor particularly tasty, I suspect. But, but you see this happening on, on different islands, so it's really important in Hawaii as well. Um, uh, and, and it can also happen on what we call Sky Island. So, um, if you like, mm, mm, seeing mountains as, as island in a, in a, in a, in a terrestrial landscape. So for example, in the Andes, in the last two million years, the lupins have turned into shrubs and trees, producing eighty different species. It's completely mind boggling.

• 43:57Speaker 05

  Jenny, tell us towards the end now, whether you can predict which trees will survive, I mean, given the project you're involved in, which trees are going to survive? Can you model the trees against the trajectory of climate change?

• 44:15Speaker 06

  We can do that, but I don't think we can give you the answer yes. And I don't really, I think everybody's trying, but we're not there, yes. But I, I think we have to scientists use. All the tools possible. So again, going back to paleobotany, what we can do is, I think we can look at the rich fossil history of Britain and Ireland and look at what trees, what species were growing two million years ago or 25 million years ago, when we know the climate was similar to our climate future. So we're kind of going back, we're going, I can't even think where we're going, but we're going into our futures more similar

• 44:56Speaker 06

  to the warm climates of the past. For example, in Ireland, the west coast of Ireland, Connemara, two million years ago, we had pecans. We had Japanese umbrella pine that's today only found in Japan. And then if you go further back, 25 million years ago, the whole of Northern Ireland, Northern Britain was covered in swamp cypress. And these trees are, you find them today in Alabama and the bayous of America, and they're extinct from Europe today.

• 45:30Speaker 05

  So presumably that means that the soil that exists in Ireland is good enough or adaptable enough to once again host trees like that?

• 45:42Speaker 06

  Yeah, I suppose, I suppose it gives me a lot of hope that they're, you know, I kind of said, well, we don't know what's resilient, but we know that biology is incredibly resilient. Bill's given us wonderful examples and it's amazing how rapidly things can adapt to their environments.

• 46:01Speaker 05

  Well, on that note of optimism, I'd like to thank my guests, Bill Baker, Chris Berry and Jenny McElwain. Next week, we'll be discussing Machado de Assis, the grandson of freed slaves and the towering figure of Brazilian 19th century literature. Thank you for listening.

• 46:24Speaker 05

  A few minutes of bonus material from Misha and his guests. I sometimes start off by saying, is there anything else you want to add? But I wanted to ask a question first of all, and that is the relationship symbiotic or otherwise between animal life forms and trees as they evolve. How do animals impact on trees?

• 46:49Speaker 03

  Who wants to go? I guess it might be easier to try to address that in the flowering plants because in a sense, a lot of the evidence is still there and the experience of seeing birds pollinating and insects doing their thing is around us all the time and leads us to suspect that, for example, you know, okay, it's not a tree, but the fact that there are 25, 30,000 species of orchid is probably to do with their pollination interactions. And it's worth saying, I mentioned earlier that when we look at how the flowering plants have diversified over time, we see this big rush at the beginning, but there's actually

• 47:29Speaker 03

  also a sort of follow-up rush that is observable in the sort of 40 million year kind of area. And we struggle to work out what that might be. But one of the, one of the reasons for that could be positive feedbacks from the growth of important, the evolution of important animal lineages that then lead plants to diversify. I haven't given you a tree specific answer because that's a bit, that's a bit harder to tackle, but.

• 47:55Speaker 05

  But I mean, presumably, I mean, trees are mentioned in the introduction about trees being used by human beings in a variety of ways, but clearly they provide shelter and a cooler environment for animal species. I mean, if you look at the, the rainforest, it's, it's teeming with animal life because of the trees, so they couldn't exist without those trees.

• 48:17Speaker 06

  You can see you've hit us. We're, we're not zoologists. We've gone very quiet.

• 48:25Speaker 07

  One of my favourite examples of this would be from the Carboniferous, so the Carboniferous Forest. Probably worth saying that if people want to go and see fossil forest in Britain, then head to Victoria Park in Glasgow or to the Brumbo Fossil Forest near Wrexham. You can see big fossil lycopod trees in the ground. There's even a beach in Wales, which, bit of a secret at the moment, but where you can see similar things. And in Nova Scotia on Joggins, there is a fantastic place called Joggins Fossil Forest, where you can see the bases of these lycopod trees, just like as in Britain.

• 49:04Speaker 07

  But 100 or more years ago, it was found that there were reptiles actually in the trees and that they were living or falling into the bases of these rotting trees. And some of our best evidence of what early reptilian life was like comes from inside these trees. So that's quite remarkable.

• 49:25Speaker 06

  And I think also even if you don't have a good fossil record of the animals or the, you know, the insects, we have trace fossils, so we have the indirect evidence. So often we will look at the fossil leaves and we can see very diagnostic feeding behaviour. So we see mining and margin feeding, feeding and hole feeding. And in some cases, colleagues and Penny Bottas have been able to identify the first occurrence of a beetle or the first occurrence of a bee, not based on the body fossil of the animal, but on the, its diagnostic feeding behaviour.

• 50:03Speaker 05

  On the leaf.

• 50:05Speaker 06

  Yeah, preserved on the leaves.

• 50:06Speaker 05

  And what about, Bill, you mentioned gigantism. What about in trees, things like the sequoia, the redwood, the redwood forests in, I mean, you know, I've seen, I haven't seen the big fat ones, but I've been in San Francisco to see these unbelievably tall, tall trees. How did they emerge?

• 50:26Speaker 06

  So we know that the tallest living tree recorded is about 116 metres tall. And I was looking at a good analogy, I think Big Ben is around 80, 90 metres, so it's taller than Big Ben. And there's a group of physicists mainly and plant scientists in Berkeley, and they actually did a really nice theory paper and they asked... What is the limit of tree height? And they determined it's about a hundred and forty metres. And what limits that a tree from ever getting taller than that is that that wood, those xylem cells suck water up under tension and negative pressure.

• 51:07Speaker 06

  And the water has to get from the roots all the way up to the leaves at a hundred and thirty metres tall of the tree. And you you break that flow of water. And Bill mentioned it in his palm. So you break the flow. And the leaves at the top of the tallest tree are actually almost living in a desert. They're so water starved that a tree cannot get taller. Because they would no longer be able to photosynthesize because they need water to exchange for carbon. And so the limit of tree height is a hard line. It's about a hundred and thirty five metres. Nothing is ever can get taller or has got taller that we know of.

• 51:45Speaker 05

  And this may be a stupid follow up question, but in somewhere like the Amazon, where you have these monumental rainfalls, the the flying, the the so called flying river. Is there any way that the canopy can extract water other than sucking it up from the ground?

• 52:03Speaker 03

  I don't think so. It's uh you're nodding. Yeah, okay, I'm like, I'm out of my depth here. What's the story?

• 52:09Speaker 06

  So I suppose fog, so you can get deposition of fog onto a leaf surface. And most of the water supply is up from the roots. But, you know, plants, they actually can take up a certain amount of moisture through their their cusicle. And but it's a tiny, tiny amount, yeah.

• 52:27Speaker 05

  So what else did we miss out in the program?

• 52:29Speaker 03

  I just wanted to make another plug for the palm family, if I may.

• 52:33Speaker 05

  Please do.

• 52:34Speaker 03

  Uh, that, yeah, is the the hundred and something metre sequoia is totally awesome. Um, but the palms still beat that in terms of total stem length. Not in a tree form, but there is a a whole group of palms that have evolved from trees to become climbers, the so called rattans of the cane furniture industry. And the the longest stem that that doesn't sort of root along its length was reported to be something like. Two hundred metres long. I think there was said to be a longer one, but an elephant chewed it up before it could be measured. But it isn't, it's a pretty poor point to score there Jenny, because of course the rattan is constantly slipping out of the canopy and

• 53:19Speaker 03

  it's not two hundred metres in vertical height. It's producing coils of stem on the floor, which so it's not having to deal with that tug of war against gravitational pull.

• 53:31Speaker 05

  And tell me Chris, in terms of those trees which grew along the ground, the first trees, do they exist anymore anywhere?

• 53:42Speaker 07

  So not in the, it's an extinct group of plants, but if you do go into tropical forests, you can see all sorts of plants which have very, very similar habits, usually using trees, upright trees as a sort of prop, and sometimes with little prop roots and things. And when we had to reconstruct what this plant looked like, we did go into a botanical garden and go round and look at some things which might have a similar sort of reason for being and so on, and look for a model, which is what I quite often do. I go, because anybody listening to this who's a botanist would be going, Chris, he's

• 54:22Speaker 07

  not a botanist. I think it's quite obvious that I'm the geologist here. But I do like going into botanical gardens and looking at the plants and trying to work out how they grow, why they grow, and what are the analogies to these really ancient plants. And so that there are analogous things, but there's not the same thing.

• 54:40Speaker 05

  And can someone tell me about the wallamy pine and what the wallamy pine is and why it's important?

• 54:46Speaker 07

  So the wallamy pine is a beautiful tree, which three of my colleagues have in their gardens, growing at various different heights. It's one of an example, like the dawn redwood and various other things, of a plant which has a morphology which you can sort of see in the past. It's related to agathus and to aracherry and various other types of coniferous trees. From my point of view, it was discovered in Australia relatively recently and it's been cultivated and spread around around the world. From my point of view, I I like it because it's an example, I've been looking for years and years. Using this analogy example for a vertical upright trunk.

• 55:32Speaker 07

  Which just has small leafy branches coming off it to see how far a tree can get that's just has small leafy branches. And it does that, it produces small leafy branches and I had a photograph of one from the park in Cardiff. In my on my phone and I thought I've got to go back and see that because it was about two metres tall when I took the photograph. I just went back to see it and it's now eight metres tall, it's absolutely gorgeous. And with these leafy branches. Eventually, some of those branches will start turning into subsidiary trunks and growing upright and they'll do all sorts of interesting things. But at the moment, it's a really nice analogy for the sort of early archaeoptery trees that we have from.

• 56:12Speaker 05

  Yeah, so they came from, they came from Australia, right?

• 56:16Speaker 07

  Correct, yes, from the wallamy.

• 56:18Speaker 05

  And thought they were thought to be extinct, is that right?

• 56:22Speaker 06

  Yeah, so I think it's really remarkable that. A tree was discovered not known to science and it was, I think it was. Climbers or abseilers and they went down into a gorge outside Sydney. Very inhospitable, you know, people don't go there and found this grove of trees. So for conservation purposes, botanic gardens all over the world now host. Wallamy pines, but also genetic variants of them and this is, it's called a conservation horticulture collection, so it's a way of. Ensuring the longevity of that incredible tree into the future by kind of. Sending it to other places to look after kind of like plant zoos.

• 57:07Speaker 06

  We we actually have included it in our Witness Tree project, so it is one of our trees that we're monitoring every year. To see how it responds to climate change and also to see how it takes up atmospheric pollution in the city environment.

• 57:19Speaker 05

  Yeah, because it was, it wasn't in city environments at all, was it?

• 57:24Speaker 06

  No, not at all.

• 57:24Speaker 03

  But it seems to be tough as old boots.

• 57:26Speaker 06

  It's incredible.

• 57:26Speaker 03

  I mean, it's growing like the clappers at Kew and yeah, really.

• 57:30Speaker 05

  You've got a wallamy too.

• 57:32Speaker 03

  We've got quite a few, yeah.

• 57:35Speaker 05

  Well, I think I shall be visiting Kew once again fairly soon. And if I may, when I next go to Dublin, Jenny, I will come and see the Trinity Botanic Gardens.

• 57:47Speaker 06

  Me too.

• 57:47Speaker 05

  Yeah.

• 57:48Speaker 06

  You're welcome.

• 57:48Speaker 05

  Well, thank you very much. I think we all deserve a cup of tea or a cup of coffee.

• 57:52Speaker 03

  That'd be good.

• 57:53Speaker 05

  Oh, here he comes.

• 57:55Speaker 07

  Tea or coffee?

• 57:56Speaker 03

  Coffee.

• 57:56Speaker 06

  I can let myself have a coffee now because it doesn't matter if I speak too quickly.

• 58:01Speaker 07

  Coffee would be gorgeous, thank you.

• 58:03Speaker 06

  Thank you.

• 58:03Speaker 05

  Tea, please.

• 58:04Speaker 03

  There are plenty of coffees on the tree.

• 58:05Speaker 06

  Coffee is a tree.

• 58:06Speaker 03

  Oh.

• 58:07Speaker 06

  And chocolate is a tree.

• 58:08Speaker 03

  And tea is really, if you let it go, if you weren't permanently removing it to make tea.

• 58:13Speaker 07

  Yes.

• 58:14Speaker 06

  In Our Time with Misha Glenny is produced by Simon Tillotson and it's a BBC Studios production.

• 58:22Speaker 01

  This is a nightmare. I need to get out of here because I do not want them to see me. A search across borders in some tricky situations. Shoot, there's a boat in the back of that car. Yeah, there is. No, no, no, no, don't get out. Watching smugglers who bring thousands of people to the UK. They have guns, they have knives, they have no shame. And at the top, a man who keeps his identity well hidden. If they know I'm talking about him, they come tonight, they will kill me. Pop, pop, pop, pop.

• 58:50Speaker 05

  Can we find out who he is? From Radio 4, this is Intrigue to Catch a King. Listen first on BBC Sounds.

• 59:02Speaker 05

  Hello, Misha Glenny here. Before you listen to this episode, I wanted to share some exciting news. You can now watch this episode and all future episodes of In Our Time in full video. Just search for In Our Time on YouTube or watch episodes 28 days early by subscribing to the streaming service, BBC Select in the US and Canada.