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knotweed, a genus of annual and perennial herbs, less frequently, semishrubs and shrubs, of the family Polygonaceae. Their stems are erect, prostrate, or sometimes twining. The perianth is usually a corolla of four to six small leaves: there are four to eight stamens and two to three styles. The fruit is triquetrous or lenticular, remaining more or less fully enclosed in the perianth. There are 300 species, mostly found in temperate and tropical regions. In the USSR there are more than 120 species.
From a biological point of view several species are particularly interesting. Willowgrass (Polygonum amphibium) is found in two forms, an aquatic one and one growing in moist places (one form is capable of transforming into the other); serpent grass (P. viviparum) has lower flowers that are mostly turned into bulblets and used for vegetative propagation. Many members of the genus have economic value. Bistort (P. bisunta), peachwort (P. persicaria), knotweed (P. aviculare), and several others are used in medicine. The extract or infusion of the dried terrestrial sterile and fertile stems of water pepper (P. hydropiper) is used as an an-tihemorrhagic substance, primarily in the case of uterine hemorrhages; it is also part of the composition of the antihemorrhoidal “anestezol” suppositories. Middle Asian representatives of the genus known by the name alpine knot-weed (P. alpinum, P. coriarium, and others) are used as tanning substances.
Knotweed. black bindweed (P. convolvulus), and copse knotweed (P. dumetorum), are weeds. The last two species, as well as the cultivated (as an ornamental) fleece flower (P. baldschuanicum), are often distinguished as a separate genus, Bilderdykia. Three species of Polygonum—Sakhalin knotweed. cuspidate knotweed. and Weirich knotweed, all with a large amount of greenery—are good fodder plants. Many members of the genus are good nectar plants. Some species—for example, P. tinctorium—can be used to obtain dyes.
REFERENCESAtlas lekarstvennykh rastenii SSSR. Moscow, 1962.
Webb, D. A., and A. O. Chater. “Polygonum L.” In Flora Eu-ropaea, vol. 1. Cambridge, 1964.
M. E. KIRPICHNIKOV