Fastest plant in the world

What's the difference between these two pictures?






If you haven't heard of trigger plants, you should have. The genus Stylidium is the fifth largest genus in Australia in terms of species – after Acacia, Eucalyptus, Grevillea and Melaleuca.

It is also arguably the fastest plant in the world - the difference between these two pictures happened in less than a blink of the eye.

Botanist Juliet Wege, at the Western Australian Herbarium, has discovered more than 20 new species of Trigger Plant in recent years, all of them in south-west Australia which has nearly three-quarters of all Trigger Plant species. There are a couple of species in Asia, quite a lot in northern Australia, and only four around Sydney.

I gather the first species was discovered in Botany Bay in 1770 by Banks & Solander, and if you look in various plant guide books they usually say there are 110-140 species in the genus Stylidium. Juliet Wege says there are at least 230 known species and maybe another 70 to be discovered.

Trigger Plants are in flower now around Sydney. Look for a stalk of small pink flowers up to half a meter tall sticking out of a tuft of coarse ‘mondo grass’-like leaves. On the Hawkesbury Sandstone the leaf tuft is at the end of a short stem, and this is a different species to the one found on clay and other sandstone (with the leaf tuft right at the base). The flowers look a bit like a little butterfly, with 2 pairs of petals (there is a fifth which is small and hidden), but they also have this amazing ‘trigger’.

The trigger is made from the fused female and male parts of the flower (the style and the anther filament). When an insect, or tiny stick held by a child or excited adult, touches the sensitive area at the base of the trigger, it flicks back into the middle of the flower dumping pollen on the insect (or relieving the insect of pollen from an earlier flower). Look at the front flower in the two pictures I took this morning and you see the trigger cocked on the left, and released (by an excited adult) on the right.

Apparently this response happens within 20 milliseconds of the area being touched! It will reset itself, slowly, taking about 30 minutes. But it may not be receptive to touch again for another 30 minutes after that.

If you are wondering, the rapid response seems to be due to the collapse of specialised cells rather than a slower change due to osmotic potential differences (where cell walls are elastic and expand and contract as salt concentrations varied) which is responsible for plant responses such as sundews enclosing their insect prey.