Feeling Triggered

Spring flowers - the magic of Trigger Plants

Spring in our part of the world is synonymous with wildflowers. The yellow-green and grey-green bush suddenly springs alive with many small and often rather strange flowers in a bold assortment of colours and the season can be tracked on the appearance of the different varieties.

One of the more unusual flowers that grow along our daily bush “commute” (ie. where we walk the dog) are Trigger plants, and now in early October we’re currently enjoying the widest range of them.

Trigger plants belong to the family Stylidium and there are about 300 species, most of which are Australian. In fact about 70% of Stylidum species are endemic to Western Australia’s Southwest, making us a biodiversity hotspot for these distinctive plants.

There is great diversity in the type of trigger plants, from trailing vines to adorable, tufty pincushions that look like fairy seats. The flowers are what makes them the most identifiable though, with most having 4 petals in sets of 2 (the majority of flowers have odd numbers of petals). They also have their characteristic “trigger”. We have a number of varieties on our normal walk, including white, yellow and pink-petalled varieties.

The trigger is a small, hammer-like appendage, tucked behind the flower petals. When the flower feels the poke of an insect proboscis, which can be mimicked with a fine stick, or something like a grass tree leaf, the hammer (with anthers on it rich with pollen) will pop forward in 15-30 milliseconds and “boop” the insect on it’s back, transferring the pollen to take on to the next flower. As the flower matures and the pollen has been sent on its way, the anthers are pushed aside for the development of a stigma, and the hammer now acts as a receptacle, to receive pollen from the insect’s back. Amazingly, all trigger plant species “boop” in a slightly different location on the insect, so there is no cross pollination and the right flower type will always get the right pollen. Some hit from the top, some from the side. Studies have indicated an incredible amount of accuracy in the hit of the hammer. After about 20 minutes, the hammer jerkily resets back to the original position, ready to go again. On warmer days, the trigger responds and resets faster, as insects will also move faster in warmer weather.

Here's a video I very awkwardly took. Can you spot the moment the trigger goes off. It's very hard to film tiny flowers when there's any wind!

If you happen to be out walking in bushy areas in mid-late spring nearly anywhere in Australia, but particularly in Western Australia’s South West, keep an eye out for these natural curiosities.

If you want to read a bit more about trigger plants and see some pictures of a good selection, including some relatively new discoveries, pop over to fresh science.org