Waterwheel plant (Aldrovanda vesiculosa) is the only extant species of flowering plant of genus Aldrovando in the family Droseraceae. It is widely distributed in Asia, Africa, Australia and Europe. Waterwheel plant is also one of the few plants which is capable of rapid plant movement. The plant used traps similar to that of the Venus Flytrap to capture small aquatic invertebrates. The common name derives from the traps that are arranged in whorls around a central, free-floating stems.
Waterwheel plant is a rootless aquatic plant, and floats just below the water surface. Adult plant has floating stems reaching 6-11 cm long with a shoot diameter of 1-2 cm. There are 12-19 whorls along the stem, like spokes in a wheel. Each whorl consists of 5-9 leaves, 7-11 mm long. The distance between grown up whorls is 0.5-0.7 cm. When in growth, the oldest whorls and internodes at the rear die, and new whorls are formed at the apex.
The leaf consists of a dorsally flattened petiole, 5-9 mm long, and 4-6 pointed bristles, each 6-8 mm long. The bristles function as a protection to the trap from being unintentionally closed by floating debris in the water. The petiole is important for photosynthesis and contains air pockets which help the plant float.
The trap has a leaf blade which consists of two semicircular lobes that fold together to form a snap trap, twisted so that the opening are pointed upward. The margin of each lobe is bent inward and lined with 60-80 small teeth. The central zone of the trap is lined with a fine coating of 30-40 trigger hairs, each 0.5-1.5 mm long, of which 18-20 are found near the midrib and 7-9 at the enclosure boundary. When in contact with aquatic invertebrates, the trap will snap shut in a rapid movement of 10-20 milliseconds, one of the most rapid movements found in plants.
Waterwheel plant produces small, solitary, 8 mm white flowers that are supported above the water surface by short, 5-15 mm long, peduncles which emerge from whorl axils. The flowers are brought under water for seed production after a few hours of opening. The seeds of waterwheel plant are cryptocotylar, with the cotyledons remain inside the seed coat and serve as energy storage for the seedlings.
Propagation is by seeds, vegetative reproduction and stem cuttings. In optimum conditions, the main shoots usually branch every 3-4 cm, giving rise to short lateral branches in the axils of the whorls.
Waterwheel plant (Aldrovanda vesiculosa) http://commons.wikimedia.org/wiki/File:AldrovandaVesiculosaHabit.jpg Jan Wieneke
http://commons.wikimedia.org/wiki/File:AldrovandaVesiculosaHabit.jpg
Jan Wieneke
