3 SEEDS
Aldrovanda vesiculosa is a rootless aquatic plant; seedlings develop a short proto-root, however this fails to develop further and senescence. The plant consists of floating stems reaching a length of 6–40cm (2-16 inch). The 2–3mm (0.08-0.1 inch) trap leaves grow in whorls of 5-9 in close succession along the plant’s central stem. The actual traps are held by petioles which hold air sacks that aid in flotation. One end of the stem continually grows while the other end dies off. Growth is quite rapid (4–9mm (0.15-0.35 inch)/day in Japanese populations), so that in optimal conditions one or more new whorls are produced each day.
The actual traps consist of two lobes which fold together to form a snap-trap similar to that of the Dionaea muscipula (Venus fly trap), except that they are smaller and underwater. These traps, which are twisted so that the trap openings point outward, are lined on the inside by a fine coating of trigger hairs, snapping shut in response to contact with aquatic invertebrates and trapping them. The closing of this trap takes 10-20milliseconds, making it one of the fastest examples of plant movement in the kingdom. This trapping is only possible in warm conditions, when water temperature is about 20°C (68°F). Each trap is surrounded by between four and six 6–8mm (0.23-0.31 inch) long bristles which prevent triggering of traps by debris in the water.
The small, solitary white flowers of Aldrovanda vesiculosa are supported above the water level by short peduncles which arise from whorl axes. The flower only opens for a few hours, after which the structure is brought back beneath the water level for seed production. The seeds are cryptocotylar, meaning that the cotyledons remain hidden within the seed coat and serve as energy storage for the seedlings. Flowering is however rare in temperate regions and poorly successful in terms of fruit and seed development.