Wallum Study Group
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Plant Name: Stylidium graminifolium
- Common Name: Trigger Plant
- Family: Stylidiaceae
A species found in the sandy soils of the Wallum, as well as sandstone and granite from the mountains to the coast. The leaves are grass like, with flowers appearing in spring and summer. In this area, they grow prolifically, at any time of the year, soon after fire, creating a pink blanket against the charred area. Flowers can vary from magenta pink to pale pink, sometimes white, and grow usually to a height of 60 cm either as a single spike or in a small bunch.
A feature of these plants is an unusual and ingenious mechanism that utilises insects for propagation. The flowers consisting of five pink petals, surround sensitive filaments united to a central column which combine both male (stamen) and female (carpel or pistil) sex organs. The central column is bent backwards and downwards like a trigger, so when the flower is touched by an insect, the column whips instantly across the centre of the flower. This action is as sharp and rapid as a mousetrap, and startles the insect with a smart blow. What happens next depends on whether the flower is young or old, as the flower, being bi-sexual cannot fertilise itself.
If the flower is young, pollen grains are released from the stamen at the end of the column, and as the insect struggles to free itself, the pollen grains stick to the hairs on its body, it eventually flies away, as it must, to deposits its burden on another flower if the cycle of life is to be repeated.
If the flower is old, the stamen has ceased it production of pollen, and the tip of the column is bare, the female part grows larger and takes it place at the head of the column which now becomes a hairy brush or cushion. Now, this time when the column snaps over to strike the visiting insect it picks up the pollen, thus cross pollination between different plants is ensured.
Within a period ranging from a few minutes to half an hour the spring column resets itself ready for the next visitor.
There are 110 known species of trigger plants in Australia (four are found in Tin Can Bay). Each species uses its own species of insect targeting a different part of the insect's body, avoiding the risk of hybridisation. The family of plant has survived from the Jurassic Period when Australia was part of Gondwanaland.