A Primer on Trigger Plants

I would like to introduce you to another group of plants capable of abrupt movements. Whereas many species have evolved moving parts in order to capture prey or deter herbivores, the following genus moves as means of achieving pollination. Meet the genus Stylidium a.k.a. the trigger plants.

Native to parts of Asia and Australia, these beautiful little herbs are quite diverse, making generalizations difficult. Still, there is one thing they all share, a fused set of reproductive organs that lash out at unsuspecting pollinators. When a visiting insects of sufficient size lands on a flower, its weight causes a rapid change in turgor pressure within the column's tissues.

The rapid change in pressure sends the column flying. The position of this reproductive hammer varies from species to species. Some bash their pollinators on the back whereas others strike them under the abdomen. When the flowers first mature, only the male portions are mature. Thus, the initial visit dusts the insect with pollen. Once the pollen is gone, the column resets itself and the female portions start to mature. The next time an insect visits the bloom, the stigma will do the bashing. With any luck, the visiting insect will have already been dusted with pollen from a previous plant. In this way, the plant avoids self pollination.

Another morphological aspect shared among member of this genus is the production of glandular trichomes. These minute hairs cover the body of the plant and produce sticky mucilage that ensnares tiny insects. It was originally thought that this was a merely a defense mechanism that may represent a form of proto-carnivory.

However, analysis of the mucilage revealed that plant is also producing digestive enzymes capable of breaking down insects unfortunate enough to have been caught. It remains to see whether or not the plants absorb nutrients in the same way as sundews but the fact that these plants share the same nutrient-poor habitats as many other Australian carnivores lends some credibility.

Photo Credit: http://bit.ly/2hJjMyc and Francis Nge

Further Reading: [1] [2]