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  • The Waterwheel plant (Aldrovanda vesiculosa) is the sole species in the flowering plant genus Aldrovanda of the family Droseraceae. This plant feeds on small aquatic invertebrates using traps very similar to those of the Venus Flytrap. The traps are arranged in whorls around a central, free-floating stem, hence the common name. This plant is one of the few plants capable of rapid plant movement. While Aldrovanda vesiculosa is monotypic, extinct species of the genus are thought to have existed [1][2]. There is also wide variability among populations of significantly different geographic locations, as the species is found natively on four continents. Morphology The waterwheel plant is a rootless aquatic plant; only seedlings possess rudimentary roots, which however soon die off. The plant consists of floating stems reaching a length of 6-11 cm [3]. The 2-3 mm 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 (4-9 mm/day in Japanese populations [4]), so that in optimal conditions a new whorl is produced once or more a day. Trap The actual traps consist of two lobes which fold together to form a snap-trap similar to that of the venus fly trap. 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 a mere 0.01-0.02 seconds[5][6], making it one of the fastest examples of plant movement in the kingdom. This trapping is only possible in warm conditions (20 °C) [7]. Each trap is surrounded by between four and six 6-8 mm long bristles which prevent triggering of traps by debris in the water. Reproduction Germinating Aldrovanda seeds Flowers The small, solitary white flowers of the waterwheel plant 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. The waterwheel plant, however, seems to bloom seldomly, at least in temperate regions. Divisions The waterwheel plant reproduces most often through vegetative reproduction. In favourable conditions, adult plants will produce an offshoot every 3-4 cm,[8] resulting in new plants as the tips continue to grow and the old ends die off and separate. Due to the rapid growth rate of this species, countless new plants can be produced in a short period of time in this fashion. Distribution The Waterwheel plant is the most widely distributed carnivorous plant species, but native to Europe, Asia, Africa, and Australia. It is, however, rare in all of its range. Aldrovanda is spread mainly through the movement of waterfowl - plants sticking to the feet of a bird are transported to the next aquatic destination on the bird's route. As a result, most Aldrovanda populations are located along avian migratory routes. Habitat The Waterwheel Plant prefers clean, shallow, warm standing water with bright light, low nutrient levels and a slightly acidic pH (around 6). It can be found floating amongst Juncus, reeds, and even rice.

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