Darwin's Most Wonderful Plants by Ken Thompson

Author:Ken Thompson
Language: eng
Format: epub
Publisher: Profile
Published: 2018-10-24T16:00:00+00:00

Close-up of a Utricularia bladder. The trap is triggered when prey touch the long trigger-hairs around the entrance.

It’s an ingenious process – and one that can be of use to humans, too. Recently, in Portugal, I met a designer who builds swimming ponds in which the water is cleaned by natural processes. To help to control the larvae of mosquitoes and other aquatic insects, he adds Utricularia to the water. Apparently it works, and, for the botanically inclined swimmer, it adds a new dimension to the whole experience.

And, before taking leave of bladderworts, I have to mention Utricularia humboldtii, whose only known habitat is the water tanks of Brocchinia, the only unambiguously carnivorous bromeliad. How weird is that?

But butterworts and bladderworts do not exhaust the Lentibulariaceae. There is a third genus, Genlisea, rootless like the bladderworts, some species aquatic, some terrestrial, but entirely tropical. Darwin devoted the final few pages of his Utricularia chapter, indeed the last section of his book on insectivorous plants, to Genlisea, and made remarkable observations, despite having only preserved specimens to work on (sent, as usual, from Kew by Hooker).

Genlisea has ordinary leaves, but below ground (or underwater) it has leaves modified into the most peculiar traps. The solid, thin lower part of the leaf opens into a bulb and then contracts into a tube that divides at the end into two spirally contorted arms, hence the common name ‘corkscrew plants’. The arms have narrow openings and small animals, such as nematodes, protozoa, rotifers, worms, crustaceans and mites, enter and cannot escape owing to numerous backwardly directed hairs. Eventually they end up in the bulb where they are digested and the nutrients absorbed. The whole thing resembles a traditional eel-trap, as Darwin noted: ‘animals are captured by Genlisea … by a contrivance resembling an eel-trap, though more complex.’ Darwin didn’t know what persuaded prey to enter the trap, but the latest research has shown that the plants secretes chemicals that attract prey into the trap.

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