Persicaria lapathifolia (L.) S.F. Gray - Knotweed.
Taxonomy.Family Polygonaceae Juss., Genus Persicaria (L.) S.F. Cray.
Synonyms.Polygonum lapathifolium L., Polygonum tomentosum Schrank.
Morphology and biology.Annual spring plant. Stem erect or procumbent (30-60 cm, rarely up to 1 m), branchy, in upper part glandular. Leaves lanceolate, linear, rarely ovate or oblong (4-40 cm), above long-pointed, downwards wedge-shaped, with short petioles and sometimes with dark stains, with or without arachnoid hairs. Inflorescence is short bunch up to 4 cm length and 1.5 cm thick. Perianth 4-separate, usually with yellow sessile glands, greenish or redish. Fruit is two-sided nut, 2.5-3.5 x 1.0 x 2.0 mm. Surface of the nuts bare, black-brown, shiny.
Distribution.Boreal circumpolar species (not native in south-west Greenland), south to the Mediterranean, Iraq, the Himalaya, central China, south Japan, Mexico; also in tropical and south Africa, south-east Asia, Australia, New Zealand, South America.
Ecology.Water favoring plant. Prefers soils containing podzol, turf and brown soils. Habitat: weed plant in the fields of different cultures (in Middle Asia - on the fields of rice), on ruderal places, on seashores and shores of lakes and rivers, mainly on stony, sandy ground. Species grows along irrigation canals, oasis in the deserts, semi-deserts. Flowers in July and August, bears fruit in August and September.
Economic value.Opportune harvesting of crop and early autumn plowing, cleaning of seeds, space between rows cultivation of the land, careful cultivation of the fallows.
Reference citations:Agaev M.G., ed. 1988. Main agricultural weeds in crops of the Leningrad Region. In: Catalogue of VIR world collection. Leningrad: VIR. N. 468: 15-17. (In Russian)
Jonsell, B., ed. 2000. Flora Nordica. Stockholm. V. 1: 243-246.
Keller B.A., ed. 1934. Weed plants of USSR. Leningrad: AN USSR. V. 2: 86-87.
Komarov, V.L., ed. 1936. Flora USSR. Moscow-Leningrad. V. 5: 649-650.
Ramenskiy L.G., Zazenkin I.A., Czishikov O.N., Antipin N.A. 1956. Ecological evaluation of the fodder objects by vegetable cover. Moscow: Selkhozgiz. 472 p.