Purple bladderwort

The bladderwort (called Utricularia by botanists) is the biggest family of carnivorous plants. In the Kaas plateau we saw large fields of purple bladderwort. The plant is aquatic: it floats on the thin film of water trapped above the stone of the plateau. The long stalks of the plants grow leaves at intervals. The bladders, which give the family its name, grow along the leaves and usually stay below the surface of water. Bladderworts are widely known to be carnivorous plants. Their bladders trap tiny invertebrates. I later found that this two hundred year old picture of carnivory may be wrong.

Plants turn to carnivory when the soil is poor in nutrients. However, they do not give up photosynthesis; their leaves are still green with chlorophyll. Carnivory gives the plant nutrients like phosphorus and nitrogen which are in short supply in the soil. The first blow to the idea of purple bladderwort being carnivorous came from careful measurements of the animals found in the bladders. These showed that at most 1% of the nitrogen and phosphorus that the plants need can come from the animals.

Purple bladderwort

Yet more amazing is that each of the bladders seemed to contain a whole live ecosystem of the small invertebrates which were trapped. New bladders did not have them, and older bladders had more animals. So it seems that the purple bladderwort is not a carnivore. It must gain something else by sustaining this ecosystem inside itself. Unfortunately no one knows yet what the plant gains from this. But it seems that the purple bladderwort (named for the purple flowers you see in these photos) may not be a carnivore.