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Waterwheel plant
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Aldrovanda vesiculosa, known as the waterwheel plant, is the sole extant 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.
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Encyclopedia
Aldrovanda vesiculosa, known as the waterwheel plant, is the sole extant 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 the genus Aldrovanda is monotypic, extinct species are known to have existed. There is also wide variability among populations of significantly different geographic locations, as the species is found natively on four continents.
Morphology
A. vesiculosa 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 . 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 ), 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, making it one of the fastest examples of plant movement in the kingdom. This trapping is only possible in warm conditions (20 °C) . 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
Flowers
The small, solitary white flowers of A. 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. The waterwheel plant, however, seems to bloom seldom, at least in temperate regions.
Divisions
A. vesiculosa reproduces most often through vegetative reproduction. In favourable conditions, adult plants will produce an offshoot every 3-4 cm, 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.
Turions
Winter-hardy Aldrovanda form so-called "turions" as a frost survival strategy. At the onset of winter, the growth tip starts producing highly reduced non-carnivorous leaves on a severely shortened stem. This results in a tight bud of protective leaves which, being heavier and having released flotational gases, breaks off of the mother plant and sinks to the water bottom, where temperatures are stable and warmer. Here it can withstand temperatures as low as -15 °C (-5 °F). In the wild, Aldrovanda turions have been observed to have a relatively low rate of successful sinking. Those nutritious turions that fail to sink are then grazed by waterfowl or are killed by the onset of frost. In spring when water temperatures rise above 12-15°C, turions reduce their density and float to the top of the water, where they germinate and resume growth. Non-dormant turion-like organs can also form in response to summer drought.
Distribution
A. vesiculosa is the most widely distributed carnivorous plant species, 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
A. vesiculosa 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.
Botanical history
A. vesiculosa was discovered in India in 1699 by Leonard Plukenet, who named the plant Lenticula pulustris Indica. The modern botanical name originates from Giuseppe Monti, who described Italian specimens in 1747 and named them Aldrovandia vesiculosa in honor of the Italian naturalist Ulisse Aldrovandi. When Carl Linnaeus published his Species Plantarum in 1753, the "i" was dropped from the name (an apparent orthographic error) to form the modern binomial.
Infraspecific taxa
- Aldrovanda vesiculosa var. aquitanica Durieu ex Diels (1906) nom.illeg.
- Aldrovanda vesiculosa var. australis Darwin (1876)
- Aldrovanda vesiculosa var. duriaei Caspary (1859)
- Aldrovanda vesiculosa var. verticillata (Roxb.) Darwin (1876)
See also
External links
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