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(duckweed), a genus of perennial herbs of the family Lemnaceae. The small plants occur on or below the surface of water. They are in the form of green round or elongate leaflike plates, from which a long root departs. The flowers are unisexual and lack a perianth. The inflorescence consists of one pistillate and two staminate flowers, which are arranged in lateral depressions of the “leaf and are surrounded by a membranous spathe. The indehiscent and saclike fruit contains one to seven seeds. Duckweeds flower very seldom. There is, however, intensive reproduction by means of budding of the leaflike structures. The plants often form a solid covering on the surface of standing water.
There are approximately ten species, distributed almost throughout the world in standing and slow-moving freshwaters. In the USSR there are three species: ivy duckweed (L. trisulca), common duckweed (L. minor), and gibbous duckweed (L. gibba). Of the three, the gibbous duckweed is the least common. Duckweeds serve as food for waterfowl and, sometimes, as fodder for swine, ducks, and geese.