Discovery of the Water Wheel Plant near Cape Le Grand

The Water Wheel Plant (Aldrovanda L.) is an aquatic carnivorous plant related to the sundews (family Droseraceae).

The sole species in Western Australia, Aldrovanda vesiculosa L., is a rootless plant, free floating near the surface of usually shallow (less than 1 m), still, standing freshwater pools which are rich in organic matter. Growth occurs at the top of the plant whilst the basal parts die off and decompose. The average plant is 20-26 cm long with 30-35 whorls of leaves on petioles along the stem, each whorl having 6-8 leaves. The leaf petioles have air chambers which help the plant to float.

This genus of carnivorous plants have a remarkable insect trap which consists of 2, usually green, semicircular leaf blades which close or snap shut within 0.1 to 0.2 seconds when a prey item (a small water animal) touches the leaf surface.

Australian plants are usually red in colour due to exposure to sunlight for more than 2 hours. Flowers are small with 5 white petals, and are exposed just above the water surface. Flowering is continuous during the warmer months. New plants are either formed from seeds or when a new branch is formed from the parent plant and drops off.

Birds play an important role in the distribution of the plant as plant parts or seeds may get stuck on the bird's feet or feathers. Flooding and flowing water are other dispersal methods.

The monotypic genus Aldrovanda is distributed throughout the world, but considered very rare. In Australia it is scattered in NSW, Queensland and the Northern Territory. In Western Australia it had been collected just once in the Kimberley in 1993, until it was discovered in a swamp near Esperance in 2008. The plant's ecological requirements are very strict and it is very sensitive to change. In many parts of the world it is thought to be declining due to changes in its environment from human impacts such as water drainage and pollution.

The Aldrovanda flower
Figure 1. Aldrovanda vesiculosa flowers are small with 5 white petals, and are exposed just above the water surface. Flowering is continuous during the warmer months. Photo: R.L. Barrett.
Aldrovanda leaves modified as insect traps
Figure 2. Aldrovanda vesiculosa insect traps consisting of 2 semicircular leaf blades. Photo: R.L. Barrett.

Written by Skye Coffey; 7 October 2009.