Instant Genius - Why leaves are one of nature’s most versatile creations

Episode Date: October 11, 2026

From the neatly curated English country garden to the wild jungles of the Amazon, the Earth is host to a staggeringly diverse range of plant life. One of the key reasons for the great evolutionary success of plants is the wide-ranging versatility and utility of the leaves that grow on them. In this episode we’re joined by Prof Jonathan Silvertown, an evolutionary ecologist based at the University of Edinburgh, to talk about his latest book, Nature’s Magicians – How Leaves Conjure Up Our World. He tells us how plants act as one of the natural world’s master chemists, explains how they contain internal clocks that allow them to track the time of day and even the time of the year, and details how they detect and respond to light, sounds, and even predatory attacks. Take your curiosity further with a subscription to BBC Science Focus magazine. Every issue is packed with fascinating insights into the science behind everyday life, the latest breakthroughs and expert analysis, delivered straight to your door. Receive an extra £5 when you subscribe using the code SF5OFF, (minimum spend £20, see full terms and conditions on our website). https://www.ourmediashop.com/bbc-science-focus-magazine-pod30 Learn more about your ad choices. Visit podcastchoices.com/adchoices

At Capital One, we don't just use technology. We architect it. Our teams have true end-to-end product ownership, shipping distributed systems that handle high concurrency at scale. No single-server bottlenecks, engineered beyond legacy downtime, and operating right here in downtown Toronto. That's Technology at Capital One. Search Technology at Capital One, Canada.

Hello, and welcome to Instant Genius, a bite-size master class in podcast. form. Every Monday and Friday you'll hear world-leading scientists and experts talking about the most fascinating ideas in science and technology today. I'm Jason Goodyear, commissioning editor at BBC Science Focus. From the neatly curated English country garden to the wild jungles of the Amazon, the earth is host to a staggeringly diverse range of plant life. One of the key reasons for the great evolutionary success of plants is the wide-ranging versatility and utility of the leaves that grow on them. In this episode, we're joined by Professor Jonathan Silverton, an evolutionary ecologist based at the University of Edinburgh to talk about his latest book, Nature's Magicians, How Leaves

Cunger Up Our World. He tells us how plants act of one of the natural world's master chemists, explains how they contain internal clocks that allow them to track the time of day and even the time of year, and details how they detect and respond to light, sounds, and even predatory. attacks. So welcome to the podcast. Thanks so much for joining us. Thank you, Jason. Pleasure to be here. So today we're talking about your latest book, Nature's Magicians, How Leaves Conjure Up Our World. So as the title suggests, it's about the many sort of fascinating properties that leaves have. So let's start with the basics then. So we all know that leaves are the green structures found on plants. But as a biologist, you know, how do you define them? In the first 50 million years of

plant evolution on land, there were no leaves. How do we know if we define them? Well, there were none of, there were stems. We don't want to stem is a cylindrical thing. It's green. These the early ones were. They had stomata on them, the little pores through which water vapor escapes and carbon dioxide enters. And they, managed to get by doing photosynthesis without these laminar structures. There we are, there we are. It's a laminar structure that sticks out at an angle from a plant stem on a little stalk called a petio. So you mentioned their photosynthesis. So that's sort of one of leaves key signature magic tricks. And we all learn in school that, you know, they take in carbon dioxide,

breathe out oxygen, it's powered by light. But that that's probably the extent of of our knowledge. So let's start with this sort of, you call them sort of like solar panels. So how do they respond to light? How do they collect energy from light? Well, yes. So leaves are packed full of, or the cells in leaves are packed full of chloroplasts. And the photosynthetic machinery is inside the chloroplast. Chloroplast themselves are fascinating. And they have an independent evolutionary history when you go back. So we could come back to that if you like. So what's happening is that the leaves essentially have evolved as, I think as almost like display cases for pluroplasts. So there's a whole lot of physics and biology and chemistry

about leaves. A lot of it is to do with light capture, not all of it. And that's the thing. The leaves are very multifunctional things. They also are sort of in charge of how water moves through the plant. And that's really important because it's water, the turquoise that keeps cells expanded, that keeps stems standing upright, keeps leaves. And so, so they're multifunctional. In the book, you say that leaves capture about 1% of the energy from sunlight. And that sounds like pretty inefficient. And you talk about, you know, we often think of the perfection of nature. So, you know, what can we say about that? Well, on the perfection of nature, it doesn't exist, is what I can say about that. Why,

after we look at stuff and how beautifully adapted, our eyes are for seeing and our other bits and pieces are for walking around, et cetera, our brains are for doing podcasts. And we think this is wonderful. But evolution doesn't have any direction. So it's not aiming for perfection. Basically, the way evolution works or natural selection works, that's been more precise,

is that it favours those organisms with characteristics, that transmit themselves referentially to the next generation. And if being photosynthetic does that for you, then those organisms that are capable of photosynthesis will be favoured over those others that are not. And if they're slightly better at the photosynthesis, if that improved photosynthetic capacity actually means you transmit more offspring,

you have more offspring, then it'll be favoured. But if it's simply better at capturing light, but that doesn't actually turn into more seeds, or more importantly, more descendants, more successful seeds, if you like, then natural selection doesn't care. So if we're judging the effectiveness of the efficiency, the energy efficiency, if you like, of a light capture of a leaf, by the standards that we would use for a solar panel, we will quite rightly say, well, this is appalling. If I try and sell you a solar panel and you say, well, this sounds very interesting,

you know, and you mean these solar panels grow? And I say, yes. And so he says, well, where's the catch? And I say, well, I'm afraid it's only 1% efficient. You put the phone down. So would I. So, but it's good enough. And that's one of the many extraordinary things.

There are so many. I mean, just to mention another one. plants are extracting an extremely rare gas from the atmosphere. Before industrialisation, it was about 0.02% of carbon dioxide in the atmosphere. It's now over 0.04%, but that's still tiny. And that's what wood is made of. This rare gas is turned through photosynthesis and using the energy of sunlight into something as solid as the table that I'm

sitting out now or the chair that you might be sitting on. This is extraordinary stuff. Yeah, so let's sort of stick with photosynthesis for a bit before we move on. Because as I said, like if a lot of people would say, oh, you know, name 10 things that plants do, one of them would probably most people would say photosynthesis. But there were organisms that existed millions of years before plants that actually photosynthesized themselves. Yes, there were. And in fact, plants have inherited that. So you're talking about cyanobacteria. And the whole history of this, which we now understand through gene sequencing

and reconstructing evolutionary trees, otherwise known as phylogenies, of the genes involved in photosynthesis. And they go back an extraordinary length of time. So life emerged on Earth around for, billion years ago. And it seems likely that photosynthesis appeared about three and a half billion years ago in some form of bacteria. It didn't emerge in cyanobacteria. This is really weird. So nowadays, cyanobacteria are photosynthetic and chloroplasts are actually, in evolutionary history, captured cyanobacterial, things like cyanobacteria that were captured by

earlier eukaryote cells and they became photosynthetics as a result. So how do we know that? Well, chloroplasts have their own DNA. Well, the only things that have DNA are cells that can reproduce. So bacterial cells, eukaryote cells, animal cells and so on. So if chloroplasts, which live inside plant cells, remember, if they have DNA, and we know this pretty clearly now, they had an independent existence. as free-living bacteria, as bacteria.

But it turns out that the genes that confer this ability on cyanobacteria are older than cyanobacteria or older than photosynthetic cyanobacteria. So they came from somewhere else where we don't really know. So the genes for photosynthesis are even older than chloroplasts, around 3.5 billion years old. That is incredible. So let's have a look at some of the other of these magicians. properties of leaves that you talk about. You know, anyone who's walked around in the evening and things like that, you know, certain plants

kind of, they change along with the cycle of the day. So you talk about, you know, plants like animals having an internal clock. Yes, they do. The cells have clocks. What's fascinating is that they're coordinated because, I mean, you know, there are billions of cells in, you know, a large plant, just as they're on in your eye. And somehow they have to be coordinated. And this happens actually through cells in the flume.

The flume is this network of tubes that carries food from the leaves down to the rest of the plant. And it turns out, this is a fairly recent discovery, that the coordination is actually carried out through cells in the flow on the borders of the flow. Yes, there are clocks and they are very important. After all, if a plant, if an organism, such as a plant, an autotrophic organism, we call them, so in other words, it feeds itself. It doesn't eat other organisms. It creates its own food, hence the light and CO2 and water, which are like the feedstocks for a plant. Those things, particularly the light, of course, are available only some of the day. So everything about a leaf has to be kind of ready for that when sun up and ready for what happens when the sun goes down.

And of course, the sun is not only transmitting light, but also when that light hits the surface, it creates heat. And the heat is a real issue as well. And leaves have to cope not only with absorbing light in this part of the spectrum, only about half the spectrum, is photosynthetically active. So that's where we talked about how leaves are about 1% efficient at capturing light. the first loss is basically they aren't able to capture the full spectrum of radiation. It's about half of it. So it goes from 100% coming from the sun to about 53% in the right spectrum, the right ballpark, you might think. And then losses continue from there.

Yeah, so let's move on to the idea of plants having senses. So most people will know about phototropism, for example. You know, we're talking about light. And you can see in the way that Southern grows, that it's growing towards the light. You think, well, you know, that makes perfect sense. But you also talk about other senses, and especially the one that you talk about, is the response of plants to sound and vibrations, like they have a sense of hearing. Well, not, this is where, let me just add a caveat here.

When we say that plants are sensitive light, we don't mean they can see. Right. There's no image. There's no image capture going on in a plant. It is, of course, sensitive to light, and plants will bend towards the light, very obviously. There are occasionally, by the way, plants that will actually bend away from light towards darkness. That's another story. So plants don't hear in the way that listeners to this podcast are hearing what I'm saying.

but they do have a sense of touch that's mediated by these dull hairs called trichomes and certain frequencies vibrate those trichomes and it turns out that there's a study I mean these things sound extraordinary but it's all of them in the literature there are certain plants that appear to be able to respond to the sound of a caterpillar munching and now they must be picking this up through these little trichomes, which seem to be tuned to that sort of wavelength. And then they respond by upping, up regulating,

increasing the concentration of chemicals in the leaf that deter caterpillars. And in the last 10 to 20 years, we've learned an extraordinary amount about how sophisticated plants are. and most of this stuff is happening in leaves, which is why we're talking about it today. But people think about the plants doing this, yeah, but it's in the leaves mostly. I guess their sense of hearing, such as it is,

given the caveat I've just mentioned, is really related to these touch sensors. Not that different to how it works in animals as well. Ultimately, it's about something vibrating and a cell detecting those physical movements. because of course, sound is pressure waves, so it kind of makes sense. So the touch sensitivity is fascinating. People have done experiments where every day they've run their fingers across a little pot of

Arabidopsis, this plant biologists use like the drosophila, the fruit fly, or the rat or the mouse of the animal biologists, the plant biologists use this thing called Arabidopsis, Thale Cress, short-lived. of plant, small plant related to mustard. And apparently if you kind of, you know, touch it daily and then compare it with a control, they grow much more poorly. The ones that you've kind of touched during, you know, over a period of a couple of weeks can be much smaller than the ones that haven't been, well, the controls, the ones that haven't been treated like that. And this is the trichomes again. And you think, well, what's going on here? And it turns out that the trichomes actually

and touch is part of the way that plants find their way around each other. So the thing we have to remember about plants is they're always surrounded by other plants. So they're competing. There are times when they, in a sense, cooperate.

And the trichomes are a way of sensing that there's another plant there and there's a fascinating experiment which has been done. So the lovely thing about using Arabidopsis, like using Dresophila, there were different mutations that enable you to find out, you know, okay, so what's the importance of this gene? We'll knock that gene out in Dresophila and then see what difference it makes. You can do the same thing in Arabidopsis. And when you knock out

the sense of touch in Arabidopsis seedlings and grow them surrounded by controls, by ordinary plants, they get overtopped. They can't find their way through the canopy. And the wild type, if you like, the control plants that have the sense of touch actually do better. And so here's a perfect example of natural selection would work, because the disabled plants, the plants that have no sense of touch will, of course, leave no offspring. And that's the end of that. We can only do this experiment because you can engineer mutations into sail crest. I doubt that there are any wild sail crest plants out there, and there are millions of these things all over the place. They'll be growing in the cracks of

the pavement as you walk to work or whatever. It's most unlikely that any of them carry that mutation because it would be very rapidly removed by natural selection. At Capital One, we don't just use technology. We architect it. Our team's have true end-to-end product ownership, shipping distributed systems that handle high concurrency at scale, no single server bottlenecks, engineered beyond legacy downtime, and operating right here in downtown Toronto. That's technology at Capital One. Search Technology at Capital One, Canada. So how about another thing, like when we're thinking of plants, like, yeah, if we leave, probably quite often, we'll think of the herbs that we use in cooking and their beautiful fragrance and smell. So, you know, what's going on

there? Why do they produce such a vast degree of these different aromatic compounds? What do we know about what the kind of, you know, evolutionary purpose of those is? Well, this is the thing about plants. They are master chemists. And I like to say that plants are like the weedy school kid who's hopeless on the playing field but excels in the chemistry lab as a sort of compensation for that. It's almost me, actually. I was a weedy school kid, not much interested in football. So what do plants do when they can't run away? They protect themselves in a different way and they use chemistry. And it's reckoned that there are probably about a million different compounds made by plants. And I don't think anybody's been able to accurately count them all.

And I'm sure the numbers are going up all the time as we discover more and more. But there are certain basic classes which are known to alkaloids, for example. So that would include nicotine, caffeine, things like this. And they have biological activity. So these million different chemicals have biological activity, meaning they interfere with biochemical reactions, sometimes positively, sometimes negatively. But when it comes down to what they're doing for the plant, it's virtually always negative. So tannins, that stuff that makes your tea orange come from leaves, of course, because tea leaves are what you make your tea from. And those are present in leaves of quite high concentrations because they interfere with proteins.

Proteins include enzymes. Enzymes are essential for any organism to digest its food. So the caterpillars are coming along and chewing on the leaf. And the first thing that happens is the tannins in the leaves are interfering with the digestion of the leaf material. And of course, it's a good thing to try and poison your predators in this way, the herbivores in this way. So that in a nutshell, it's basically about defense. not just against things with jaws, but also against fungi and bacteria. The thing about all these natural enemies of plants is they all have some tell, if you like,

to use some thing about them that can alert the plant that is being attacked. Because, I mean, the basic biochemistry of anything that's alive is the same. I mean, you know, we have something like 60% of the genes of a banana, for example. So the basic processes are the same. So how do you know that you're being attacked by something that's not you, right? And bacteria, many often have a flagellum, a little tail. So that's one way in which plants can tell they're being attacked. If suddenly the proteins in a flagellum, which are characteristic, are detected by a plant,

it responds accordingly by increasing the concentration of antibacterial compounds and the leaf. So this creates a selection pressure against four bacteria that can hide. So there's a very common bacterium called pseudomonas that sometimes is pathogenic, sometimes not, on leaves. And there are strains that use the flagellum to invade, they need it because they need it to move into the plant. They need to get into the plant, often through the stomata, little holes in the leaf. But once they're inside, they multiply, and their offspring have no tails.

They actually jettison their tails. Well, they don't produce them, I think, rather than jettison them. Because if they hang on to them, the plant then, you know, can react against those. So there's this constant, it's been described as an arms race, between natural enemies and plants. In fact, this is true of animals and us as well, evolution of COVID virus, for example. Yeah, so it's sort of sticking with that idea. So, you know, there's a huge variety of the different shapes and textures of leaves.

And so, you know, we've all picked up stinging nettle or something or touched a sharp plant and got, you know, got pricked by it. So that's the same sort of idea, isn't it? They're all defence mechanisms to keep various things away. from them. Yes, they are. I mean, when you can't run away, you know, other other mechanisms of defence evolve for the kinds we've just been talking about. And you mention nettles. So one of the nice things about the nettles story is, of course, it has these stinging hairs on, which are really aimed at, I guess, mammals, things with sensitive mouths, not caterpillars, catapalers, catapalers of many species of butterfly love nettles. Nettles are very rich in the nightshed.

and phosphorus. Nettle leaves have this fairly characteristic shape, and anybody who knows some of their wildflowers will have heard of the dead nettle. And the dead nettle, which is unrelated to the stinging nettle, has leaves of quite similar shape to stinging nettles, and they often grow together. But the dead nettle, as its common name kind of suggests, doesn't sting. So I'm not aware of anybody who's actually tested out whether this is mimicry. But it's certainly a good hypothesis that dead nettles are imitating, again, not deliberately, this is the natural selection at work, if it's true. They're imitating something that animals be wary of eating in order to benefit from the same defence, essentially, without having to produce stinging cells or anything else.

Yeah, so let's flip this around then to some examples of plants that, you know, insectivorous plants, the most famous of which is the venous fly trap, which I'm sure, you know, everyone's aware of. But, you know, it's got these jaw-like growth in it. So, you know, how does that, what happens? How does that work? You know, how does it capture a fly? We understand this in quite some detail now. So basically, looking at the jaws, by the way, they're often, red-colored, which on the inside. They're leaves, by the way. These jaws are leaves. On the

inside, they're often red, which is attractive to flies. Some flies like red anyway. They think it's meat, I guess. And there are these little trichomes, these hair inside, three on each of the leaves. So you imagine there's a pair of leaves, and each of them, the left half and the right half, have these three triggers, their hairs. And if one of them is triggered on a leaf, nothing happens. If two of them are triggered, then within 30 seconds of each other, it doesn't have to be simultaneous. Then the jaws snap shut.

And basically, it's a fascinating mechanism that depends upon a combination of things, that the structure of the two leaves, which are sort of bowed outward slightly, like if you imagine a pair of symbols, you know, musical symbols. And this is maintained by hydrostatic pressure, by water inside the leaves, kind of in the cells of the leaves,

maintaining this shape. And when the right stimulus arrives, these two of these, trichomes are touched, they generate an electrical impulse that changes the water pressure in the cells of the leaf and they then collapse inwards, essentially then closing the leaf. That's a rather approximate definition of explanation, but it's fascinating stuff. And what's extraordinary is it's the only plant we know of that does. that works like that. It's just there's one species in this genus Dionea that does this thing.

There are other plants that use similar tricks, but nothing quite, well, some of them are small and living water so we don't tend to see them very much. Bladderwort is one that actually has these little bladders that have a little trap door that operates a bit like the leaves of a Venus flytrap. Yeah, so we've talked about the ability of plants, thanks to their leaves. leaves, to be able to sort of, you know, in a way, sense things that are going on around them. And we talk there about, you know, the mechanism by which the Venus flytrap can catch and consume a fly. So in the book, sort of by way of a sort of final question, you talk about this, which I gather you're not very much of a fun of. Is this idea of plant neurobiology,

you know, do plants display any signs of intelligence? Well, it's an understatement to say I'm not a family. I spend a chapter in the book explaining why not. And the reason why one even bothers to talk about this, or why I'm even bothered to talk about it, is because others are obsessed with the idea and have published some very successful books based on this idea. So if you're into this kind of thing,

you will know exactly which books I'm talking about. And there's not one, there's about half a dozen or a dozen of them. The first problem is, what is intelligence? And psychologists, you know, are someone, have some difficulty over this. At the moment when, you know, artificial intelligence is in every news bulletin, there's evident confusion there too about, you know, whether what amounts to a sophisticated matching exercise with, you know, the entire contents of the internet is intelligent, or is there just, you know, smart searching.

general intelligence is clearly a lot more than that. But what can a plant do? So this is the issue. Can a plant do anything that you could describe as intelligent as what your dog could do, right? I mean, dogs can learn things. They do learn things. That's one reason why they make good pets is because you can teach them not to poop all over the carpet, stuff like that. But is there evidence that plants can learn?

none whatsoever. None whatsoever. So how could you, I mean, this is a short version, you know, the long version you can read. So how could an organism that can't learn be intelligent? Because it can't remember anything in its experience and so on. Now, somebody on the other side of the argument would say, oh, but there are plants that can learn. For example, they can, they know whether they've been through winter. So this is absolutely so, or they know that the, you know that the, the total number of sunlight hours in the day has changed. So that must require some kind of memory. Well, it's the sort of memory that your toaster has, right?

Because, you know, your toaster is programmed to deliver toasted bread of a particular colour, which can be changed to your liking. So you can say, I want it, you know, black almost burning, or I can have it, you know, scarcely toasted at all, and you can set that on a dial. And, of course, your toaster responds accordingly. But why does it do so? Because it's been designed to give you these options.

And that's the kind of intelligence that plants have. Essentially, in the experiments I described earlier, where, for example, if they have intact trichomes, they can find their way through a canopy of leaves to at least keep up with the Joneses, with the plant Joneses, you know, and not be overshadowed, is that intelligence? Well, no, it's adaptation.

And when you push certain people who are of the plant intelligence persuasion on this, they will say things like, but all life is intelligent because it's adapted. To which I reply, well, we understand adaptation. Why call it intelligence? You know, I mean, adaptation is a well-understood process.

We tie it to genetics, to genes, to chemistry, you know, to population genetics. This is not new. And it is exciting and it is extremely productive science. It works. Calling plants intelligent doesn't tell us anything. So if you want to define intelligence, so loosely that it includes plants, what is it telling you about plants or anything else that you wouldn't otherwise know? And my answer to that is zero.

Thank you for listening to this episode of Instant Genius, brought to you from the team behind BBC Science FACUS. That was Professor Jonathan Silvertan. To discover more about the topics we've just discussed, check out his book, Nature's Magicians, How Leaves Conjure Up Our World. If you liked what you just heard, then please do consider subscribing to Instant Genius on your preferred podcast platform. If you'd like to see our guests and hosts in person, then why not check out our YouTube channel at Science Focus. If you've enjoyed this podcast, why not take your curiosity a step further with BBC Science Focus magazine? Receive an extra £5 off when you subscribe using the code SF5 off. For more details, see the show description.

The current issue of BBC Science Focus magazine is out now. Pick up a copy wherever you buy your favourite magazines or download us on your app store of choice. You can also find us on Apple News or online at sciencefocus.com. At Capital One, we don't just use technology. We architect it. Our teams have true end-to-end product ownership, shipping distributed systems that handle high concurrency at scale. No single-server bottlenecks. beyond Legacy Down Time and operating right here in downtown Toronto.

That's Technology at Capital One. Search Technology at Capital One, Canada.