Original subtitles

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.