Kingdom of Plants: Life in the Wet Zone
Plants aren't quiet green wallpaper. Speed them up and they shove and climb to reach the light; look closer and you'll find frogs living in their leaves, flowers that fire pollen like darts and a pitcher plant that a tree shrew uses as a toilet. In the hothouses of Kew, David Attenborough traces how plants left the water and conquered the land.
How Did Charles Darwin Predict a Moth Nobody Had Ever Seen?
That a moth with a tongue just as long must exist. Nothing else could reach the nectar and carry the pollen. Nobody had ever seen such a moth, and many people laughed. In 1903, 21 years after Charles Darwin's death, a hawkmoth with a tongue about a third of a metre long was found in Madagascar. It was named praedicta: the predicted one.
Because flowers and their pollinators shape each other. A flower that rewards one kind of animal and an animal built to reach that reward evolve together over millions of years. David Attenborough calls this partnership the key to why flowering plants spread so fast and became so many.
Put Your Instincts to the Test
Rainforest plants have plenty of warmth and water, but they still have problems to solve. Pick an answer for each question, then see if your instincts were right.
The water rolls off and takes the dirt with it. The leaf is covered in microscopic bumps that hold drops up off the surface, so only about 2 per cent of the water touches the leaf itself. As the drops roll away they carry dirt and germs, so the leaf cleans itself.
It collects its own pond. Broad leaves channel the daily rain into a watertight tank at the centre; some hold up to 50 litres. Insects and tiny poison frogs live in the pool, and their droppings become the plant's fertiliser.
It's a toilet for tree shrews. The lid oozes a sweet treat. To lick it, a mountain tree shrew has to sit with its rear end right over the pitcher, so its droppings fall in and feed the plant. It's even been suggested that the treat works as a laxative.
Understanding the Science
Tap each card to follow plants from the water's edge to the flower-filled forests of today and the clever partnerships they made on the way.
Key Concepts
The Battle for Light
Tap to learn moreSpeed up time and plants stop looking peaceful. In the warm, wet rainforest they push and climb in a desperate race for light. Vines reach around for another plant to hitch a ride on. Bamboo, a giant grass, can grow a whole metre in a day and reach 30 metres, as high as a nine-storey building.
Too Much Water
Tap to learn moreIn a rainforest the problem can be too much rain. Taro leaves are covered in microscopic bumps that hold water up in round drops, so only about 2 per cent of each drop touches the leaf. The drops roll off carrying dirt and germs with them, which keeps the leaf clean enough to keep catching light.
From Water to Land
Tap to learn moreThe first plants were slimy algae at the edges of rivers and swamps. Some later grew a waterproof coat and crept onto damp land as liverworts and mosses. Later still, their descendants stiffened their stems so they could stand upright: the ferns and horsetails. As plants spread they pumped out oxygen, so animals could follow them out of the water.
Pollen on the Wind
Tap to learn moreTo make seeds, pollen from one plant has to reach the eggs of another. Conifers such as pines, yews and firs leave that to the wind. They make enormous clouds of pollen grains, barely bigger than specks of dust, which can drift for hundreds of kilometres. It works, but it's wasteful: millions of grains are lost for every one that lands in the right place.
Darwin's Abominable Mystery
Tap to learn moreAbout 140 million years ago, halfway through the age of the dinosaurs, flowering plants appeared and quickly split into a huge number of species. Charles Darwin called it an abominable mystery, because he expected evolution to be slow. Scientists now point to two things happening together: a doubling of the plants' genetic material (which let them change faster) and a new partnership with animals.
Flowers and Insects Evolve Together
Tap to learn moreEarly flowers, like the ancestors of water lilies, used bright petals to advertise pollen to insects, which carried it from flower to flower. Insects favoured brighter petals, stronger scents and sweeter nectar, so plants evolved them. In turn, insects evolved bigger eyes, stronger wings and longer mouthparts to make the most of the flowers. Each side drove the other to diversify.
Tricks and Counter-Tricks
Tap to learn morePassion vines and heliconius butterflies have been in an arms race for millions of years. The butterflies' caterpillars eat the leaves, so some vines evolved poison; some caterpillars then evolved to store that poison and use it against their own predators. Some vines fight back with fakes: tiny yellow spots on their leaves look like butterfly eggs, so a female thinks the leaf is already taken.
Plants That Eat Animals
Tap to learn morePitcher plants grow in poor soil, short of nitrogen and minerals, so they get them from animals. The pitcher is a leaf shaped into a trap, coloured and scented to lure insects. Its rim is slippery with wax and tiny ridges; inside, the fluid behaves like quicksand, and enzymes dissolve whatever falls in. Some large pitchers even catch the odd mouse.
Try It: From Water to Land
Plants start as algae in a river. Choose a kind of plant and click the land to plant it. Green enough of the land and the next trick evolves, until flowers cover everything.
Each new trick let plants live a little further from water. Mosses still need a film of water for their sperm to swim; ferns need damp ground for the tiny plants that grow from their spores; seeds and wind-blown pollen freed conifers from water altogether; flowers brought insect partners. The faint green band shows where your chosen plant can survive. Hundreds of millions of years pass in a few minutes here.
Wildlife of the Wet Zone
Meet some of the remarkable plants David Attenborough finds in Kew's glasshouses, along with the animals that depend on them.
Bamboo
Tap to learn moreA giant grass and the fastest-growing plant of all. Some kinds can shoot up a whole metre in a single day and reach 30 metres, as tall as the rainforest trees around them. Speeded up, you can watch them race for the brightest light at the top of the canopy.
Taro
Tap to learn moreIts huge leaves shed water like magic. Microscopic bumps hold each drop up off the surface, so the water rolls away with the dirt, leaving the leaf clean and almost dry. Engineers have copied the idea to make self-cleaning surfaces.
Tank Bromeliad
Tap to learn moreIt grows high on branches with no soil at all. Its leaves press together to make a watertight tank that can hold up to 50 litres of rainwater. The pool becomes a home for insect larvae and tiny frogs, and their waste feeds the plant.
Mimic Poison Frog
Tap to learn moreA Peruvian poison frog no bigger than a thumbnail. Some spend their whole lives, from tadpole to adult, in and around bromeliad pools high in the canopy. It's the first frog found to be monogamous: pairs stay together and share the work of raising their young.
Giant Amazon Waterlily
Tap to learn moreKew built a whole glasshouse for it in 1852. Its flower can close completely, trapping beetles inside for hours so they're sure to be dusted with pollen before they're let out. The ancestors of water lilies were among the very first flowering plants.
Comet Orchid
Tap to learn moreA star-shaped white orchid from Madagascar with its nectar at the bottom of a spur about 30 centimetres long. It led Charles Darwin to predict a moth with a tongue long enough to reach it. At night, the hawkmoth that was finally found does exactly that, pollinating the orchid as it drinks.
Bee Orchid
Tap to learn moreThe lower lip of this little orchid looks like a bee, and it gives off a scent just like a female bee's. A male bee that tries to mate with it carries off pollen to the next flower. Orchids can reshape that lip without changing their other petals, one reason there are so many kinds.
Rwandan Water Lily
Tap to learn moreThe smallest water lily in the world and one of the rarest. Its only wild home was a hot spring in Rwanda, and when that dried up, it was gone from the wild. At Kew, Carlos Magdalena saved it by growing seedlings in damp mud instead of water, just like the shallow spring it came from.
Apply Your Knowledge
Every one of these plants has a partnership or a trick that helps it survive. Can you match them up?
Match the Plant to Its Trick
Click an item to select it, then click the matching description to place it.
Real-World Challenge
David Attenborough says the loss of one plant can mean the loss of an insect, which can mean a bush loses its pollinator, which can mean a mammal loses its food. Pick one plant from this lesson and draw its web of connections: who pollinates it, who eats it, who lives in or on it. What might happen to each of them if that plant disappeared?
Protecting the Wet Zone Today
Rainforests hold more kinds of living things than any other habitat, which also means more to lose. Here's how botanists are helping.
Response: When the Rwandan water lily vanished from the wild, its seeds would sprout but the seedlings always died. In 2009 Carlos Magdalena at Kew tried something that sounds crazy: growing a water lily out of the water, in pots of damp mud like its old hot spring. Within weeks he had dozens of healthy plants. Botanic gardens now keep it alive while its wild home can't.
Response: Orchids are so prized that wild plants are dug up and sold. Every orchid species in the world is now covered by CITES, the international agreement that controls trade in wild plants and animals, so wild orchids can't be traded across borders without permits. Most orchids on sale are now grown from seed in nurseries.
What Has Changed Since This Documentary Aired
This documentary was first shown in 2012. Here's what botanists have found since.
Updated: Not entirely, but in 2024 a team led by Kew published the most complete family tree of flowering plants yet, built from the DNA of more than 9,500 species, including dried specimens from Kew's collections, some more than a century old. It confirms that flowering plants went through a burst of new species early in their history, just as Charles Darwin noticed.
Updated: Not in Britain. There, bees hardly ever visit it, and the bee orchid usually pollinates itself: its pollen simply flops onto its own flower. Around the Mediterranean, male bees still fall for the trick.
Updated: It's the same animal, but in 2021 scientists decided the Madagascar hawkmoth is different enough from its African relatives to be a species of its own, now called Xanthopan praedicta, the predicted one.
Test Your Understanding
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Reflection
David Attenborough admits it might seem odd to work so hard to save one small, plain water lily. Do you think it's worth it? Think about what you've learned about how closely plants and animals depend on each other and give your reasons.
Episode Discussion
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