David Attenborough: Kingdom of Plants (2012) s01e01 Episode Script
Life In The Wet Zone
I'm exploring the fascinating world of plants, from the most bizarre to the most beautiful.
I will be using today's latest technology to reveal a whole new dimension in the lives of plants.
I'll trace them from their beginnings on land to their vital place in nature today .
.
and discover a hidden world that, only too often, we overlook.
We'll move from our time scale to theirs.
We will explore the extraordinary ways by which some plants survive in the harshest conditions.
And we will do all this in one unique place, a microcosm of the whole plant world, the Royal Botanic Gardens of Kew.
Kingdom of Plants with David Attenborough I've seen plants growing in their natural habitats all over the world.
But here in Kew, it's possible to examine them in a way that is impossible in the wild.
Here, some 90% of all known plant species are represented in one form or another.
So, in this one place, you can survey the entire plant kingdom, and what is more, using 3D cameras, reveal some of its most intimate secrets.
Life in the Wet Zone Plants flourish most dramatically in places where there is a lot of warmth and a lot of water - the wet zone.
So here we can discover how plants first established themselves on land to become the very foundation of all terrestrial life.
Rainforests occupy only about 2% of the world's land surface, but they contain over 50% of the world's species.
And many of these wet zone plants have extraordinary survival strategies.
And to study them, Kew has built a rainforest here on the banks of Thames.
This is a rainforest like no other.
The Palm House was constructed in 1844 from over 200 tons of iron and 16,000 panes of glass.
No one had ever built a glass house on this scale before and to do so, the architects borrowed techniques from the ship building industry, which may explain why the Palm House looks like the upturned hull of a ship.
Its purpose was to provide a home for the tropical plants that Victorian explorers brought back from their adventures in the tropics.
It was an engineering wonder of the age.
And it is still a botanical wonder.
Most of the plants at this end of the house are kept in pots as they would have been in Victorian times.
And this is almost certainly the oldest pot plant in the world.
This is Encephalartos altensteinii.
and it came here in 1775.
Altensteinii has since been joined by a multitude of other wet zone plants.
Together they constitute a unique global rainforest, a living laboratory where we can watch and observe the fascinating ways in which rainforest plants interact and behave.
Conditions in this glass house are near perfect for wet zone plants.
It's warm, it's humid, there's plenty of light, and as a consequence, plants grow very rapidly and all through the year.
If you speed up time, plants begin to reveal their true nature.
They are not passive organisms as you might think, but competitive creatures, every bit is aggressive as animals, they are locked in a desperate battle for light and space.
They stretch and pulse as they strive to barge their way into pole position.
Creepers and vines reach around for the branch or the stem of another plant on which to hitch a ride.
Bamboos, a family of giant grasses, are capable of extraordinary speeds as they race towards the mightiest light of the top of the canopy.
They are the fastest growing of all plants.
Some species can grow a whole meter in a single day.
And at 30 meters tall, as high as a nine-storey office building, they can compete with the tallest rainforest trees.
The one resource wet zone plants don't need to fight for is water.
In fact, there can be so much rain in the rainforest that some species have to have special ways of getting rid of it.
This is the taro plant and it has the most extraordinary leaves.
What would happen when I pour water on them? The water rolls, leaving the leaf behind almost dry.
And that's because the leaf is covered with very, very tiny microscopic structures which hold aloft the droplets of water.
And as a consequence, only about 2% of water touches the actual leaf surface itself.
And as the droplets roll away, they carry with them the dirt and bacteria, so, in effect, these leaves are self-cleaning.
But there are some plants that use water in a different way and they leave high up in the canopy.
A tank bromeliad, a plant that is dispensed with the need of growing in the soil on the ground, and instead attaches itself to branches up here in the canopy where there is plenty of light.
And since it's so far from the ground, it has had to develop a technique of collecting its nutriment in a quite different way.
They collect some of the rain in everyday drenches in South American rainforest where they live.
Their leaves, which are very broad, channel the rain water into a central reservoir.
At their base, the leaves are so tightly pressed together that the tank they create is watertight.
Some species can hold up to 50 liters of liquid.
The water not only hydrates the plant, but it also provides a home for a lot of creatures that wouldn't otherwise be able to live up here.
These little wrigglers are the larvae of mosquitoes.
In the wild, there are lots of different creatures that can be found in these little pools.
This is Ranitomeya imitator, a poison dart frog from Peru.
It's the size of a thumb nail and the only monogamous amphibian in the world.
Some individuals spend their whole lives, from tadpole to adult, in and around bromeliad pools.
And high in the canopy, such a pool provides an excellent home.
It's relatively safe and there is a ready supply of food.
The plant benefits from the arrangement because the droppings produced by its lodger are a nutritious fertilizer.
Bromeliads and the frogs that live in them are only one example of the complex relationships that are bound in the rainforests.
In tropical forests, the lives of every living thing, both animal and plant, are intimately entwined.
It's a tangled web that has evolved over many millions of years.
Throughout the history, rainforests have provided plants with a refuge against harsher conditions elsewhere in the planet.
So in rainforests, you'll find some very ancient plant families.
This cycad, for example, belongs to a family that certainly provided food for the dinosaurs.
But the rainforest is such a rich environment that plants of all state in their history can still be found here.
The first was slimy thread-like algae that emerged from rivers and swamps to grow on the wet muddy margins.
40 million years or so later, some developed watertight coverings that enabled them to move on to try those still moist land.
They were the liverworts and the mosses.
Later still, some of the descendents of those plants stiffen their stems so that they were able to stand upright as they reached up towards the light.
They were the ferns and horsetails.
This greening of the earth changed the course of life allowing animals to follow plants out of permanent water.
As they spread across the land, the plants pumped out oxygen from their leaves.
So from the very beginning, land animals were dependent upon plants not only for food, but for the very air they breathe.
A major difficulty for plants in their new environment was reproduction.
If they were to produce fertile seeds, pollen from one had to reach and fertilize the ova, the eggs of another.
Conifers - pines, yews and firs - then, as now, used wind.
They produced vast numbers of pollen grains, scarcely bigger than particles of dust, which the wind could carry for hundreds of miles.
The technique was successful but very wasteful.
Immense quantities of pollen grains had to be produced if just one was to reach its target.
But then, about 140 million years ago, some developed a much more efficient way of doing that - with flowers.
How this happened was, for a long time, a total mystery to scientists, including one of the greatest.
Charles Darwin was baffled by what he called "an abominable mystery".
The fact that, half way through the age of dinosaurs, flowering plants suddenly produced a vast number of species and within a very short period of time.
That contradicted one of the characteristics of evolution as Darwin thought that it was a slow and gradual process.
How could that happen? From the moment Darwin posed the question, scientists have been striving for an answer.
Recent fossil discoveries and modern DNA analysis of species present and past have transformed our understanding of this fascinating period.
Using that information, scientists with work pioneered here in Kew have been able to construct the ancestral tree of whole of plant life.
It begins with algae, the simplest of the plants, which are followed by the mosses.
The thickness of the rising branches indicates the growth of number of species in each individual group.
For the first half of the plant's evolutionary history, all the branches of plant life flourished roughly equally.
But then, 140 million years ago, there was an explosive radiation of species - Darwin's mystery.
These were the angiosperms - flowering plants.
Their evolution was more gradual than Darwin had thought, but there is no question that the angiosperms quickly became the dominant group.
They diversified to a huge range of species which have occupied almost every known habitat on earth.
But what happened to stimulate this dramatic radiation? There was a happy coincidence of two events.
The first was a doubling in the genetic material of plants, allowing them to evolve more quickly when their environment changed The second was one such change - the development of the unique relationship between plants and animals.
The effect of this coincidence can be seen in one of the very first flowering plants to evolve.
This is the Water Lily House, the hottest and most humid environment in Kew.
It was built in 1852 to accommodate the latest botanical discovery - the giant Amazon water lily.
Now, it's February and the pond is almost bare.
But in a few weeks, exotic water lily of all kinds will be sprouting.
The ancestors of today's water lilies, as we know from their fossils, were among the first plants to produce flowers.
Bright petals, modified leaves were an advancement to flying insects.
They signal the presence of highly nutritious pollen.
The shape of the flower work like a primitive trap forcing the insects to stumble about and bumping to the flower's reproductive structures.
In doing so, the insects transferred onto the water lily pollen which they accidentally collected on earlier visits to other flowers.
So now plants could trick insects into transporting their pollen directly from one plant to another with a door-to-door service.
The flower of the giant Amazon water lily can close totally, holding the insects captive for several hours, thus making absolutely sure that pollination occurs.
Many different species of plant followed suit, each evolving its own particular flowers to attract its insect messengers.
Competition for their services drove the plants to diversify.
Insects favored petals that were brighter, scent that was more perfume, and flowers that had the sweetest nectar.
The appearance of such temptations had a huge effect on the insects.
They, too, began to diversify.
A multitude of forms could better harness the potential of the numerous species of flower.
Insects with large eyes could spot the flowers, powerful wings could carry them between plants, and complex mouth parts could delve into the deepest nectary.
So plants and insects evolved together driving their mutual diversity.
Rainforests are the combination of this process, containing a greater variety of species than any other habitat.
And here you can see that some plants didn't restrict themselves to insects.
This, for example, is known as the jade vine.
But why is it this extraordinary mesmerizing blue-green color? Well, we know that it is fertilized by bats.
That's why the flowers hang out in the open, so bats can get up them quite easily.
And so maybe this color stands out particularly boldly, as bats are concerned, in the moonlight.
When the bat arrives, it stick its head into the flower to get the honey and as it does so and presses there, out from this hook, come the stamens and dab pollen on its back.
So when the bat goes away, it takes the pollen to another flower.
Each and every species of flowering plant has its own unique evolutionary story that's closely coupled with the animals that pollinated.
But one family of flowering plant has developed this relationship in more complex ways than any other and, in doing so, has become the most numerous and diverse on the planet.
There are an estimated 25,000 species of orchid.
This family had a particular fascination for Charles Darwin as he reveals in one of his letters that is kept here in Kew.
He says, "I have been extremely much interested with Catasetum", that's an orchid, "and indeed with many exotic orchids.
"Orchids have interested me "as much as almost anything in my life.
" Charles Darwin.
One species of these amazing plants can be found growing outside in the grounds of Kew.
Orchids are extraordinary plants from many points of view.
But one of them is that the lower lip of the flower is controlled by a special set of genes.
So that means that it can evolve and change its shape and color while the rest of its petals remain the same.
The lower lip of this little orchid has evolved to look roughly like a bee.
And people used to think that was a kind of warning to warn cows not to eat it on the grounds that they wouldn't want to get stung on the tongue.
Now we know that's not the case.
This is a mimic of a female bee that's attracting a male to mate it and when the male mates, it will pollinate the flower.
How do we know that's true? Because this little flower produces the scent which is exactly the same as that of a female bee trying to attract a mate.
The unique genetic make-up of orchids has allowed them to evolve an almost unbelievable degree of complexity.
And they produce their greatest variety and complexity in the wet zone.
At Kew, they are cultivated inside the Princess of Wales Conservatory.
In this section, conditions are perfect for them.
Each orchid species has its own characteristic form and color.
They represent the pinnacle of evolutionary cooperation between animals and plants.
In their most extreme form, the relationship for the plant is an exclusive one.
Only one species of insect would have the right equipment to claim the plant's nectar.
This relationship between a particular kind of insect and a particular kind of plant produces some extraordinary results.
This, for example, is Darwin's favorite orchid - Catasetum.
Unusually for orchids, some plants are male and others are female.
This is a male.
It produces a kind of scent that attracts just one species of small, blowsy and beautifully colored bee.
The bee lands on the lip of the orchid and thrust its head into the orchid's flower itself.
And that touches a trigger and sticks onto the bee's back this extraordinary thing, which is, in fact, a bundle of pollen grains called "pollinia".
This has a little cap on it, which, after a minute or so, folds off and reveals there - that little horseshoe shaped bundle of pollen grains.
High speed cameras can show us the trigger mechanism The pollinia accelerates with great force and so ensures it sticks firmly onto the insect's back.
The bee loads out some of these, flies away, and maybe thinks it's not going to do that again, but is nonetheless attracted to another rather different looking flower, which is the female, but which produces just that sort of scent.
And it sticks it's head into the female flower and this little bundle of pollen, like a key, fits into a little aperture like a lock and it pulls off the pollen and leaves on the bee's back a little bundle.
And lo and behold - pollination has been achieved.
It's hard to imagine how evolution produce such a complex pollination mechanism.
But there is one orchid whose life story is even more astonishing.
Many flowers produce a sweet nectar to entice insects and other animals to come and pollinate.
But this orchid from Madagascar, the Comet Orchid, carries its nectar at the end of extremely long spurs in back of its flower.
What on earth could have a tongue long enough to reach down those huge long spurs? Charles Darwin who studied the fertilization of orchids decided it could only be a moth, but nobody had ever seen it.
Until some years after his death, it was proved right.
This is Xanthopan morganii praedicta, Morgan's predicted Sphinx moth.
With special night-vision cameras, we can show why a such an immensely long tongue is needed.
It's a third of a meter long, exactly the same length as the spur beneath the flower.
The relationship between orchids and their insect pollinators is certainly very intimate, but the connection between these passion flowers and butterflies is even more complex.
This is Passiflora - the passion vine.
Like orchids, its brightly colored displays attract pollinators.
One of them is a Heliconiinae butterfly.
But this relationship between the insect and the plant is not straightforward trade off.
Passion vine and butterfly have been engaged in an ongoing game of one-upmanship for many millions of years.
The butterfly doesn't just want nectar.
It also wants a place to lay its eggs, a place where its caterpillars will have something good to eat immediately nearby - passion flower leaves.
And its young have huge appetites.
But some passion vines have fought back.
They have evolved a way to protect themselves - poison in their leaves.
But sometimes even this is no defense.
Some caterpillars not only tolerate the leaf's toxins, but store them in their flesh.
And now those toxin serve as a defence against the caterpillar's predators.
And the story doesn't even end here.
The passion vine has evolved a second line of defense.
This one has leaves that give impression of being a swarm of butterflies.
By mimicking the real ones, it may be suggesting that there is no perching room for others.
And in the details of their leaves, you can see something even more surprising.
This kind of passion flower has a special way of dissuading female butterflies from laying their eggs on its leaves.
It imitates eggs with these little yellow spots so that female butterflies will think that these leaves are already taken as you might say.
And this different species of passion flower does the same thing but imitates eggs in a different way with tiny little posts at the base of the leaf.
The passion flower's tactics illustrate some of the complex ways by which plants dissuade animals from raiding them.
But some wet zone species have turned the tables.
This bud will soon become a leaf.
It's no ordinary leaf.
It has a special all together more sinister purpose.
This is Nepenthes, the pitcher plant.
It grows in nutrient poor soils, so has to find nitrogen and minerals in another way.
The leaf, just like a flower, attracts insects with a reward.
The pitcher is colored and scented to appeal to flies looking for a meal of rotting flesh.
The visitors are rewarded with a greasy substance on the underside of the pitcher's lid.
But the plant wants something in return.
Not pollen, but a meal.
The lip of the pitcher in covered in tiny slippery ridges.
Wax lubricates the surface further.
It's extremely difficult to hold on even for a fly.
Once inside, there is no escape.
The leaf holds a pool of digestive liquid.
This contains microscopic elastic pheromones which gives it the properties of quicksand.
The more the insect struggles, the deeper it sinks.
Enzymes begin to dissolve the victim's body while it's still alive.
Some pitchers aren't content with just insects.
This one eats mice.
The mice come along, perhaps attracted by the sweet nectar on the lip.
They fall in.
They can't get a purchase to get out.
They drown.
And eventually, the enzymes in the pitcher's fluid dissolve the body so that, eventually, there is nothing left but a bit of fur and bone.
This pitcher is called Nepenthes lowii.
It lives on the forested the slopes of Borneo's mountains.
And it's perhaps the most extraordinary pitcher of them all.
The evidence is that it too attracts small mammals.
It excretes a sort of nectar from the underside of the lid there and that attracts little tree shrews.
This engaging animal is Tupaia montana - the mountain tree shrew.
It feeds on fruit and any insects it can find.
It also visits pitcher plants.
Until recently, what happens next was a mystery.
This footage seems to show that the animal has found a way of evading the slippery death trap.
What is more, it's feeding on the underside of the pitcher's lid.
This pitcher doesn't get its nutriment from the bodies of dead animals.
It's got another way of sustaining itself.
The tree shrews come to lick it.
When they do, their rear end is directly over the pitcher so that their droppings fall into it.
And its that that provides this plant with its nourishment.
It's even been suggest that that nectar contains a laxative to persuade the tree shrew to do just that.
This ability of the rainforest environment over time has allowed the co-evolution of animals and plants to develop to an unrivaled degree of complexity.
But with complexity, comes fragility.
Each and every species has its own place in the complex working of the rainforest.
In recent years, Kew's unique position as a living laboratory of the wet zone has become more important than ever.
These days, Kew's role extends far beyond these 300 acres.
And here, people are working to rescue extremely rare plants.
from total extinction.
The danger of losing a single species is taken very seriously indeed.
Here in the Water Lily Room, experts face a desperate scramble to save one species from oblivion.
Nestling amongst the giant water lily pads, is the tiny Nymphaea thermarum - the Rwandan water lily - the smallest and rarest water lily in the world.
Extinct in the wild, these precious few individuals are some of the last remaining specimens.
These photographs show its only known habitat as it was over 20 years ago - A hot spring in Rwanda.
It was destroyed just recently when locals redirected its waters to supply a laundry.
A single specimen was brought back to Europe, but the species remained on the blink.
Its seeds would germinate, but the seedlings always died.
Then some seeds were given to this man at Kew - Carlos Magdalena.
Known in Spain as "the Plant Messiah", Carlos is famous for his great skill in rescuing endangered species.
But even Carlos nearly met his match with this tiny plant.
Like this did many different seedlings, nothing seemed to work.
Well, that meant that the species is about to disappear forever? Exactly, that was very worrying for me.
So I started becoming a little bit obsessed with it.
And, yes.
I mean yes, it is crazy, isn't it? To know that something that you can do or not can make a difference to a species.
Carlos didn't give up.
He had one more unlikely idea.
He tried growing the water lily out of water.
This idea, growing water lily out of water, is something as crazy as to grow a cactus floating in a pond.
So it was the last unlikely thing that logically you will do and then these are the result.
Carlos' inspired idea was to make use of this plant's strange ecological quirk.
Nearly all other water lilies only grow in deep water, but the Rwandan spring's very shallow, little more than damp mud.
And so by growing it in pot above the water, Carlos replicated its natural habitat.
Within a few short weeks, there were 50 specimens, all set to flower.
So this is a crucial moment because if this works and it's clearly going to, you have, in fact yourself, saved the species.
If I didn't have this crazy idea, the holy species will be gone forever.
That's absolutely charming.
Beautiful! In an environment with so many species and so many spectacular ones, it might seem odd to spend so much trouble and try to save just one comparatively inconspicuous one.
But the relationships within the rainforest are so complex and so extensive that the loss of just one can have a whole series of unpredictable consequences.
The loss of a plant can mean the loss of an insect.
The loss of an insect can mean that a bush loses its pollinator.
The loss of the bush can mean that a mammal has lost its food plant.
Nobody can say exactly when or if such things are gonna happen.
But to me, preventing it from happening in the first place seems to make absolute sense.
The story of plants spreads well beyond the wet zone.
They have evolved to occupy almost every environment on the planet.
They survive in regions of constant change, They thrive in soils that almost never see rain, and, as we will discover, they do much of their living in ways that go almost entirely undetected by us.
I will be using today's latest technology to reveal a whole new dimension in the lives of plants.
I'll trace them from their beginnings on land to their vital place in nature today .
.
and discover a hidden world that, only too often, we overlook.
We'll move from our time scale to theirs.
We will explore the extraordinary ways by which some plants survive in the harshest conditions.
And we will do all this in one unique place, a microcosm of the whole plant world, the Royal Botanic Gardens of Kew.
Kingdom of Plants with David Attenborough I've seen plants growing in their natural habitats all over the world.
But here in Kew, it's possible to examine them in a way that is impossible in the wild.
Here, some 90% of all known plant species are represented in one form or another.
So, in this one place, you can survey the entire plant kingdom, and what is more, using 3D cameras, reveal some of its most intimate secrets.
Life in the Wet Zone Plants flourish most dramatically in places where there is a lot of warmth and a lot of water - the wet zone.
So here we can discover how plants first established themselves on land to become the very foundation of all terrestrial life.
Rainforests occupy only about 2% of the world's land surface, but they contain over 50% of the world's species.
And many of these wet zone plants have extraordinary survival strategies.
And to study them, Kew has built a rainforest here on the banks of Thames.
This is a rainforest like no other.
The Palm House was constructed in 1844 from over 200 tons of iron and 16,000 panes of glass.
No one had ever built a glass house on this scale before and to do so, the architects borrowed techniques from the ship building industry, which may explain why the Palm House looks like the upturned hull of a ship.
Its purpose was to provide a home for the tropical plants that Victorian explorers brought back from their adventures in the tropics.
It was an engineering wonder of the age.
And it is still a botanical wonder.
Most of the plants at this end of the house are kept in pots as they would have been in Victorian times.
And this is almost certainly the oldest pot plant in the world.
This is Encephalartos altensteinii.
and it came here in 1775.
Altensteinii has since been joined by a multitude of other wet zone plants.
Together they constitute a unique global rainforest, a living laboratory where we can watch and observe the fascinating ways in which rainforest plants interact and behave.
Conditions in this glass house are near perfect for wet zone plants.
It's warm, it's humid, there's plenty of light, and as a consequence, plants grow very rapidly and all through the year.
If you speed up time, plants begin to reveal their true nature.
They are not passive organisms as you might think, but competitive creatures, every bit is aggressive as animals, they are locked in a desperate battle for light and space.
They stretch and pulse as they strive to barge their way into pole position.
Creepers and vines reach around for the branch or the stem of another plant on which to hitch a ride.
Bamboos, a family of giant grasses, are capable of extraordinary speeds as they race towards the mightiest light of the top of the canopy.
They are the fastest growing of all plants.
Some species can grow a whole meter in a single day.
And at 30 meters tall, as high as a nine-storey office building, they can compete with the tallest rainforest trees.
The one resource wet zone plants don't need to fight for is water.
In fact, there can be so much rain in the rainforest that some species have to have special ways of getting rid of it.
This is the taro plant and it has the most extraordinary leaves.
What would happen when I pour water on them? The water rolls, leaving the leaf behind almost dry.
And that's because the leaf is covered with very, very tiny microscopic structures which hold aloft the droplets of water.
And as a consequence, only about 2% of water touches the actual leaf surface itself.
And as the droplets roll away, they carry with them the dirt and bacteria, so, in effect, these leaves are self-cleaning.
But there are some plants that use water in a different way and they leave high up in the canopy.
A tank bromeliad, a plant that is dispensed with the need of growing in the soil on the ground, and instead attaches itself to branches up here in the canopy where there is plenty of light.
And since it's so far from the ground, it has had to develop a technique of collecting its nutriment in a quite different way.
They collect some of the rain in everyday drenches in South American rainforest where they live.
Their leaves, which are very broad, channel the rain water into a central reservoir.
At their base, the leaves are so tightly pressed together that the tank they create is watertight.
Some species can hold up to 50 liters of liquid.
The water not only hydrates the plant, but it also provides a home for a lot of creatures that wouldn't otherwise be able to live up here.
These little wrigglers are the larvae of mosquitoes.
In the wild, there are lots of different creatures that can be found in these little pools.
This is Ranitomeya imitator, a poison dart frog from Peru.
It's the size of a thumb nail and the only monogamous amphibian in the world.
Some individuals spend their whole lives, from tadpole to adult, in and around bromeliad pools.
And high in the canopy, such a pool provides an excellent home.
It's relatively safe and there is a ready supply of food.
The plant benefits from the arrangement because the droppings produced by its lodger are a nutritious fertilizer.
Bromeliads and the frogs that live in them are only one example of the complex relationships that are bound in the rainforests.
In tropical forests, the lives of every living thing, both animal and plant, are intimately entwined.
It's a tangled web that has evolved over many millions of years.
Throughout the history, rainforests have provided plants with a refuge against harsher conditions elsewhere in the planet.
So in rainforests, you'll find some very ancient plant families.
This cycad, for example, belongs to a family that certainly provided food for the dinosaurs.
But the rainforest is such a rich environment that plants of all state in their history can still be found here.
The first was slimy thread-like algae that emerged from rivers and swamps to grow on the wet muddy margins.
40 million years or so later, some developed watertight coverings that enabled them to move on to try those still moist land.
They were the liverworts and the mosses.
Later still, some of the descendents of those plants stiffen their stems so that they were able to stand upright as they reached up towards the light.
They were the ferns and horsetails.
This greening of the earth changed the course of life allowing animals to follow plants out of permanent water.
As they spread across the land, the plants pumped out oxygen from their leaves.
So from the very beginning, land animals were dependent upon plants not only for food, but for the very air they breathe.
A major difficulty for plants in their new environment was reproduction.
If they were to produce fertile seeds, pollen from one had to reach and fertilize the ova, the eggs of another.
Conifers - pines, yews and firs - then, as now, used wind.
They produced vast numbers of pollen grains, scarcely bigger than particles of dust, which the wind could carry for hundreds of miles.
The technique was successful but very wasteful.
Immense quantities of pollen grains had to be produced if just one was to reach its target.
But then, about 140 million years ago, some developed a much more efficient way of doing that - with flowers.
How this happened was, for a long time, a total mystery to scientists, including one of the greatest.
Charles Darwin was baffled by what he called "an abominable mystery".
The fact that, half way through the age of dinosaurs, flowering plants suddenly produced a vast number of species and within a very short period of time.
That contradicted one of the characteristics of evolution as Darwin thought that it was a slow and gradual process.
How could that happen? From the moment Darwin posed the question, scientists have been striving for an answer.
Recent fossil discoveries and modern DNA analysis of species present and past have transformed our understanding of this fascinating period.
Using that information, scientists with work pioneered here in Kew have been able to construct the ancestral tree of whole of plant life.
It begins with algae, the simplest of the plants, which are followed by the mosses.
The thickness of the rising branches indicates the growth of number of species in each individual group.
For the first half of the plant's evolutionary history, all the branches of plant life flourished roughly equally.
But then, 140 million years ago, there was an explosive radiation of species - Darwin's mystery.
These were the angiosperms - flowering plants.
Their evolution was more gradual than Darwin had thought, but there is no question that the angiosperms quickly became the dominant group.
They diversified to a huge range of species which have occupied almost every known habitat on earth.
But what happened to stimulate this dramatic radiation? There was a happy coincidence of two events.
The first was a doubling in the genetic material of plants, allowing them to evolve more quickly when their environment changed The second was one such change - the development of the unique relationship between plants and animals.
The effect of this coincidence can be seen in one of the very first flowering plants to evolve.
This is the Water Lily House, the hottest and most humid environment in Kew.
It was built in 1852 to accommodate the latest botanical discovery - the giant Amazon water lily.
Now, it's February and the pond is almost bare.
But in a few weeks, exotic water lily of all kinds will be sprouting.
The ancestors of today's water lilies, as we know from their fossils, were among the first plants to produce flowers.
Bright petals, modified leaves were an advancement to flying insects.
They signal the presence of highly nutritious pollen.
The shape of the flower work like a primitive trap forcing the insects to stumble about and bumping to the flower's reproductive structures.
In doing so, the insects transferred onto the water lily pollen which they accidentally collected on earlier visits to other flowers.
So now plants could trick insects into transporting their pollen directly from one plant to another with a door-to-door service.
The flower of the giant Amazon water lily can close totally, holding the insects captive for several hours, thus making absolutely sure that pollination occurs.
Many different species of plant followed suit, each evolving its own particular flowers to attract its insect messengers.
Competition for their services drove the plants to diversify.
Insects favored petals that were brighter, scent that was more perfume, and flowers that had the sweetest nectar.
The appearance of such temptations had a huge effect on the insects.
They, too, began to diversify.
A multitude of forms could better harness the potential of the numerous species of flower.
Insects with large eyes could spot the flowers, powerful wings could carry them between plants, and complex mouth parts could delve into the deepest nectary.
So plants and insects evolved together driving their mutual diversity.
Rainforests are the combination of this process, containing a greater variety of species than any other habitat.
And here you can see that some plants didn't restrict themselves to insects.
This, for example, is known as the jade vine.
But why is it this extraordinary mesmerizing blue-green color? Well, we know that it is fertilized by bats.
That's why the flowers hang out in the open, so bats can get up them quite easily.
And so maybe this color stands out particularly boldly, as bats are concerned, in the moonlight.
When the bat arrives, it stick its head into the flower to get the honey and as it does so and presses there, out from this hook, come the stamens and dab pollen on its back.
So when the bat goes away, it takes the pollen to another flower.
Each and every species of flowering plant has its own unique evolutionary story that's closely coupled with the animals that pollinated.
But one family of flowering plant has developed this relationship in more complex ways than any other and, in doing so, has become the most numerous and diverse on the planet.
There are an estimated 25,000 species of orchid.
This family had a particular fascination for Charles Darwin as he reveals in one of his letters that is kept here in Kew.
He says, "I have been extremely much interested with Catasetum", that's an orchid, "and indeed with many exotic orchids.
"Orchids have interested me "as much as almost anything in my life.
" Charles Darwin.
One species of these amazing plants can be found growing outside in the grounds of Kew.
Orchids are extraordinary plants from many points of view.
But one of them is that the lower lip of the flower is controlled by a special set of genes.
So that means that it can evolve and change its shape and color while the rest of its petals remain the same.
The lower lip of this little orchid has evolved to look roughly like a bee.
And people used to think that was a kind of warning to warn cows not to eat it on the grounds that they wouldn't want to get stung on the tongue.
Now we know that's not the case.
This is a mimic of a female bee that's attracting a male to mate it and when the male mates, it will pollinate the flower.
How do we know that's true? Because this little flower produces the scent which is exactly the same as that of a female bee trying to attract a mate.
The unique genetic make-up of orchids has allowed them to evolve an almost unbelievable degree of complexity.
And they produce their greatest variety and complexity in the wet zone.
At Kew, they are cultivated inside the Princess of Wales Conservatory.
In this section, conditions are perfect for them.
Each orchid species has its own characteristic form and color.
They represent the pinnacle of evolutionary cooperation between animals and plants.
In their most extreme form, the relationship for the plant is an exclusive one.
Only one species of insect would have the right equipment to claim the plant's nectar.
This relationship between a particular kind of insect and a particular kind of plant produces some extraordinary results.
This, for example, is Darwin's favorite orchid - Catasetum.
Unusually for orchids, some plants are male and others are female.
This is a male.
It produces a kind of scent that attracts just one species of small, blowsy and beautifully colored bee.
The bee lands on the lip of the orchid and thrust its head into the orchid's flower itself.
And that touches a trigger and sticks onto the bee's back this extraordinary thing, which is, in fact, a bundle of pollen grains called "pollinia".
This has a little cap on it, which, after a minute or so, folds off and reveals there - that little horseshoe shaped bundle of pollen grains.
High speed cameras can show us the trigger mechanism The pollinia accelerates with great force and so ensures it sticks firmly onto the insect's back.
The bee loads out some of these, flies away, and maybe thinks it's not going to do that again, but is nonetheless attracted to another rather different looking flower, which is the female, but which produces just that sort of scent.
And it sticks it's head into the female flower and this little bundle of pollen, like a key, fits into a little aperture like a lock and it pulls off the pollen and leaves on the bee's back a little bundle.
And lo and behold - pollination has been achieved.
It's hard to imagine how evolution produce such a complex pollination mechanism.
But there is one orchid whose life story is even more astonishing.
Many flowers produce a sweet nectar to entice insects and other animals to come and pollinate.
But this orchid from Madagascar, the Comet Orchid, carries its nectar at the end of extremely long spurs in back of its flower.
What on earth could have a tongue long enough to reach down those huge long spurs? Charles Darwin who studied the fertilization of orchids decided it could only be a moth, but nobody had ever seen it.
Until some years after his death, it was proved right.
This is Xanthopan morganii praedicta, Morgan's predicted Sphinx moth.
With special night-vision cameras, we can show why a such an immensely long tongue is needed.
It's a third of a meter long, exactly the same length as the spur beneath the flower.
The relationship between orchids and their insect pollinators is certainly very intimate, but the connection between these passion flowers and butterflies is even more complex.
This is Passiflora - the passion vine.
Like orchids, its brightly colored displays attract pollinators.
One of them is a Heliconiinae butterfly.
But this relationship between the insect and the plant is not straightforward trade off.
Passion vine and butterfly have been engaged in an ongoing game of one-upmanship for many millions of years.
The butterfly doesn't just want nectar.
It also wants a place to lay its eggs, a place where its caterpillars will have something good to eat immediately nearby - passion flower leaves.
And its young have huge appetites.
But some passion vines have fought back.
They have evolved a way to protect themselves - poison in their leaves.
But sometimes even this is no defense.
Some caterpillars not only tolerate the leaf's toxins, but store them in their flesh.
And now those toxin serve as a defence against the caterpillar's predators.
And the story doesn't even end here.
The passion vine has evolved a second line of defense.
This one has leaves that give impression of being a swarm of butterflies.
By mimicking the real ones, it may be suggesting that there is no perching room for others.
And in the details of their leaves, you can see something even more surprising.
This kind of passion flower has a special way of dissuading female butterflies from laying their eggs on its leaves.
It imitates eggs with these little yellow spots so that female butterflies will think that these leaves are already taken as you might say.
And this different species of passion flower does the same thing but imitates eggs in a different way with tiny little posts at the base of the leaf.
The passion flower's tactics illustrate some of the complex ways by which plants dissuade animals from raiding them.
But some wet zone species have turned the tables.
This bud will soon become a leaf.
It's no ordinary leaf.
It has a special all together more sinister purpose.
This is Nepenthes, the pitcher plant.
It grows in nutrient poor soils, so has to find nitrogen and minerals in another way.
The leaf, just like a flower, attracts insects with a reward.
The pitcher is colored and scented to appeal to flies looking for a meal of rotting flesh.
The visitors are rewarded with a greasy substance on the underside of the pitcher's lid.
But the plant wants something in return.
Not pollen, but a meal.
The lip of the pitcher in covered in tiny slippery ridges.
Wax lubricates the surface further.
It's extremely difficult to hold on even for a fly.
Once inside, there is no escape.
The leaf holds a pool of digestive liquid.
This contains microscopic elastic pheromones which gives it the properties of quicksand.
The more the insect struggles, the deeper it sinks.
Enzymes begin to dissolve the victim's body while it's still alive.
Some pitchers aren't content with just insects.
This one eats mice.
The mice come along, perhaps attracted by the sweet nectar on the lip.
They fall in.
They can't get a purchase to get out.
They drown.
And eventually, the enzymes in the pitcher's fluid dissolve the body so that, eventually, there is nothing left but a bit of fur and bone.
This pitcher is called Nepenthes lowii.
It lives on the forested the slopes of Borneo's mountains.
And it's perhaps the most extraordinary pitcher of them all.
The evidence is that it too attracts small mammals.
It excretes a sort of nectar from the underside of the lid there and that attracts little tree shrews.
This engaging animal is Tupaia montana - the mountain tree shrew.
It feeds on fruit and any insects it can find.
It also visits pitcher plants.
Until recently, what happens next was a mystery.
This footage seems to show that the animal has found a way of evading the slippery death trap.
What is more, it's feeding on the underside of the pitcher's lid.
This pitcher doesn't get its nutriment from the bodies of dead animals.
It's got another way of sustaining itself.
The tree shrews come to lick it.
When they do, their rear end is directly over the pitcher so that their droppings fall into it.
And its that that provides this plant with its nourishment.
It's even been suggest that that nectar contains a laxative to persuade the tree shrew to do just that.
This ability of the rainforest environment over time has allowed the co-evolution of animals and plants to develop to an unrivaled degree of complexity.
But with complexity, comes fragility.
Each and every species has its own place in the complex working of the rainforest.
In recent years, Kew's unique position as a living laboratory of the wet zone has become more important than ever.
These days, Kew's role extends far beyond these 300 acres.
And here, people are working to rescue extremely rare plants.
from total extinction.
The danger of losing a single species is taken very seriously indeed.
Here in the Water Lily Room, experts face a desperate scramble to save one species from oblivion.
Nestling amongst the giant water lily pads, is the tiny Nymphaea thermarum - the Rwandan water lily - the smallest and rarest water lily in the world.
Extinct in the wild, these precious few individuals are some of the last remaining specimens.
These photographs show its only known habitat as it was over 20 years ago - A hot spring in Rwanda.
It was destroyed just recently when locals redirected its waters to supply a laundry.
A single specimen was brought back to Europe, but the species remained on the blink.
Its seeds would germinate, but the seedlings always died.
Then some seeds were given to this man at Kew - Carlos Magdalena.
Known in Spain as "the Plant Messiah", Carlos is famous for his great skill in rescuing endangered species.
But even Carlos nearly met his match with this tiny plant.
Like this did many different seedlings, nothing seemed to work.
Well, that meant that the species is about to disappear forever? Exactly, that was very worrying for me.
So I started becoming a little bit obsessed with it.
And, yes.
I mean yes, it is crazy, isn't it? To know that something that you can do or not can make a difference to a species.
Carlos didn't give up.
He had one more unlikely idea.
He tried growing the water lily out of water.
This idea, growing water lily out of water, is something as crazy as to grow a cactus floating in a pond.
So it was the last unlikely thing that logically you will do and then these are the result.
Carlos' inspired idea was to make use of this plant's strange ecological quirk.
Nearly all other water lilies only grow in deep water, but the Rwandan spring's very shallow, little more than damp mud.
And so by growing it in pot above the water, Carlos replicated its natural habitat.
Within a few short weeks, there were 50 specimens, all set to flower.
So this is a crucial moment because if this works and it's clearly going to, you have, in fact yourself, saved the species.
If I didn't have this crazy idea, the holy species will be gone forever.
That's absolutely charming.
Beautiful! In an environment with so many species and so many spectacular ones, it might seem odd to spend so much trouble and try to save just one comparatively inconspicuous one.
But the relationships within the rainforest are so complex and so extensive that the loss of just one can have a whole series of unpredictable consequences.
The loss of a plant can mean the loss of an insect.
The loss of an insect can mean that a bush loses its pollinator.
The loss of the bush can mean that a mammal has lost its food plant.
Nobody can say exactly when or if such things are gonna happen.
But to me, preventing it from happening in the first place seems to make absolute sense.
The story of plants spreads well beyond the wet zone.
They have evolved to occupy almost every environment on the planet.
They survive in regions of constant change, They thrive in soils that almost never see rain, and, as we will discover, they do much of their living in ways that go almost entirely undetected by us.