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Plants

Plants face the same central challenge in life as animals – they strive to live long enough to reproduce. Their solutions are every bit as ingenious and cunning as that of any animal. Many plants even use animals for their own ends.

Plants cannot survive without light, so getting enough of it is critical. This is easy for plants growing in the open, bathed by the sun. But it is a huge challenge for those plants that emerge from their seeds down on a forest floor. Most of the sun’s light is absorbed by plants up in the canopy. Trees can grow up into the canopy, but most plants do not have strong enough stems to grow that tall. So some plants use tree trunks as ladders. The Boston ivy grows suckers which give it a grip on tree trunks, allowing it to grow up into the canopy. The cat’s claw creeper literally produces claws which latch onto a tree trunk to give it a grip.

But over 20,000 different kinds of plants have overcome this problem by living permanently in the canopy – these are the epiphytes. They live on the branches of big trees. But plants not only need light. They need nutrients and water. The plants on the forest floor get this from the soil, but that is not an option for epiphytes. Instead they trap dead leaves among their roots. The leaves rot to produce a kind of compost in the branches. They get their water from mist or rainwater that runs over the branches, the epiphytes roots sucking it up like blotting paper.

Where there is little rain, plants find clever ways of trapping and retaining water. The dragon’s blood tree is shaped by an umbrella with upward pointing, narrow leaves. Mist condenses on them and flows down the branches into the trunk. The shape of the dense crown also shades its roots to prevent evaporation. The desert rose loses its leaves entirely to stop evaporation and stores water inside its barrel-shaped trunk.

In boggy soil with few nutrients plants have turned carnivorous. The sundew is pinkish red and it has nectar, to attract insects. When a fly lands on the sundew, the leaf immediately curls up around its prey like a kind of fly-paper. The fly drowns in sticky fluid which digests it.

The Venus flytrap attracts insects with its pink color and a ring of nectar. If an unsuspecting fly touches two trigger-like hairs within 20 seconds of each other, the trap snaps shut, and the fly is imprisoned and slowly digested.

Plants also use animals for pollination. The cold of the windswept Tasmanian mountains threatens to kill flowers before they are mature. So the richea honey bush fuses its petals together into a protective case. This is a problem because the insects that will pollinate it can’t get in. But when the sun briefly appears the flowers warm enough to produce nectar, which attracts a bird – the black currawong. The bird pulls apart the casings to get to the nectar and, at the same time, exposes the flower inside to pollinating insects. The honey bush gets pollinated before the biting winds kill the flowers.

The Heliconia rations the nectar a purple-throated carib hummingbird can get each time it visits the plant. In this way it enslaves the bird. The bird is like an addict, returning again and again to the plant to get more nectar, each time carrying pollen from other plants.

Seed dispersal relies on yet more clever tricks. The South African brunsvigia flowers briefly before being scorched to death in the heat of the sun. Its flower heads break off and roll across the land, blown by the wind, its seeds flying out in all directions. Other plants seeds are designed to float or flutter away from the parent plant. Alsomitra of Borneo has the most aerodynamic of all plant seeds, which can float hundreds of meters through the forest.

The saguaro cactus of Arizona produces an edible coating around its seeds which encourage all kinds of animals (from birds to tortoises to ants) to eat and then spread it seeds in shady places where they can germinate away from the scorching sun.

By capturing energy from the sun and all life on land, directly or indirectly, depends on them. So, ultimately, plants fuel the diversity of life on Earth.

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