Aldrovanda- Watereheel plant
Aldrovanda vesiculosa
Map: Petr Dlouhý, Wikimedia
Aldrovanda is a monotypic genus with Aldrovanda vesiculosa as the only species. It was observed in India in 1696, but was first described in 1747 and named after the Italian botanist Ulisse Aldrovandi. The genus was then called Aldrovandia, but Linné made a spelling mistake in 1753, and it has persisted. 17 extinct species have been registered. Aldrovanda vesiculosa was previously widespread in Eurasia and southern Africa, but the map shows a dramatic decline in suitable habitats, i.e. shallow, clear ponds without Sphagnum. The European occurrence is stated too optimistically and the species is probably gone in Japan. It may still be found in the Caspian Sea and in South Africa, and has been introduced into the eastern United States.
Photo: David Short, www
Photo: Stefan Jefnaer, Wikimedia
The rootless free-swimming aquatic plant grows quickly, but rarely grows more than 20 cm long, dying back as quickly as it grows forward. The Aurasian occurrences are green, while plants from Australia are red-violet as they contain anthocyanin. The leaves are wreathed, and hence the English popular name ‘waterwheel plant’. The flowers are 5-numbered and white as in the other members of the sundew family. In temperate regions, Aldrovanda overwinters by the shoot tip forming a hibernacle that sinks to the bottom as described for Utricularia, but in warmer climates it grows all year round.
Photo: Juniper, Robbins & Joel 1989
The trap works according to the same principles as in Dionaea with mechanical stimulation of trigger hairs (6-8 per trap) and the emergence of an action potential that triggers acid growth and pressure changes in the cells around the median nerve. During folding, the shape of the leaf lobes changes from convex to concave. The prey is primarily daphnia, water fleas and small mosquito larvae. A trap can be reused 2-4 times depending on the size of the prey. The digestive glands are constructed and function as in Dionaea. The long brushes (see color photos) around the trap should prevent larger animals from triggering the clap mechanism to no avail. The 4-branched hairs strongly resemble the hairs in the Utricularia bladder, and they may help to keep the edges of the leaf lobe tightly together in the closed trap by pumping water out of the cells in the area.
H. S. Heide-Jørgensen, December 2021. Translated January 2025.