Range: Central Europe, Eastern Russia, Tropical/Southwestern Africa, Northern China Japan, Southern Asia, Australia
Possibly the only fully aquatic carnivore outside the bladderworts, this flytrap relative is scattered nearly worldwide, save the Americas (except where it has been introduced as a nonnative), in shallow, warm, and acidic waterways abundant with companion plants. The plant may reach a full size of 15 cm long (rarely to nearly 30), with numerous whorls of 5-12 leaves per whorl. Each leaf consists of a flat petiole ending in four long filaments, and a trap lamina angled 90° from the filaments. The trap is roughly the shape of a clamshell, and no more than half a centimeter in length, maybe a centimeter, and lined with numerous “teeth” on the inner edge, with up to 40 trigger hairs in the central zone. Color can be pure green or, in some forms, pure red or purple. Flowers, when they open, are produced above the water singly on short stalks, with five whitish or pinkish petals. In winter, temperate forms produce dense whorls on a short stem, called turions, which sink to the lake bed to overwinter and return to the surface in spring. This plant is often referred to as the most difficult carnivorous plant to grow.
Cultivation: Grow in a large terrarium or small outdoor pond, filled with a layer of sand, peat, and leaf litter, with 6-20 inches of warm, slightly acidic water (some have success in a simpler setup of peat moss on the bottom of a clear water container). Plant companion plants such as reeds and sedges, and introduce microorganisms for the plant to feed on and to control algae. For cold hardy varieties, when turions form either let them overwinter in outdoor ponds or cold aquariums, or store in plastic bags of water in a cold area for at least 3 months. Do not let them freeze. Sow seeds in water, and grow in diffused or full sun.
Lifespan and reproduction: perennial. Reproduces through natural divisions or seed, and may be grown through leaf or whorl cuttings.
Waterwheels are thought to be the closest relative outside of certain sundew species to the Venus Flytrap, Dionaea muscipula. Locally, they can be extremely abundant due to their rapid growth habits, but overall they are considered heavily endangered. Habitats are sparse and not just any waterway will do, and when a population dies or is killed off it can be difficult to reintroduce (after Tsunamis in Japan wiped out one of the only remaining populations there, it was only through massive restoration efforts that propagules were able to be placed back into the lake). Red forms are known from several regions, including Africa, northern Australia, and certain European regions.