Weeds
Amaranthus retroflexus L. - Common amaranth, Redroot pigweed.
Classification.
Family Amaranthaceae Juss., genus Amaranthus L.Biological group.
Annual seed-propagated aestival-autumnal weed, segetal-ruderal.Morphology and biology.
Stem is erect, up to 100 cm high, single or ramified, light green to reddish, sparse at the bottom, densely leaved at the top, with short, rough hairs. Foliage leaves are ovate, long-petiolate, bluish green, alternating, with pointed end, also usually reddish underneath. Taproot penetrates to 100 cm depth. Flowers are small, inconspicuous, massed in glomerules to greenish, dense fascicles at the stalk end or twig ends. Hypsophylls are lanceolate, almost two times longer than perianths. Perianth is pentamerous, prickle-like. Inflorescence is prickly. Boll is shorter than perianth, opens across with a cover, contains one seed. Seed is 1 mm, black or black-brownish, glossy, sharp at the edges. Shoots emerge in April-May and later, flowering period begins in June, and fruiting period lasts until late autumn. Seed dormancy is 9 months. The mass of 1000 seeds is 0.4-0.5 g. One plant can produce 5000 seeds under optimal conditions. Seeds remain viable in soil for 40 years.Distribution.
North and South America; middle and southern Europe; Mediterranean area; Asia Minor; Iran; China; Japan; Mongolia; northern Africa. In the former USSR, European part, except the Far North; and in Central Asia, Caucasus, Siberia, and Far East.Ecology.
Grows primarily on humus-rich, nutrient rich and especially nitrogen rich, permeable soils. Shoots emerge at a minimal temperature of 6 to8°C and optimum temperature of 26-36°C, with sufficient soil moisture.Economic value.
Frequently infests tilled crops, less frequently grain crops , annual fodder grasses; occurs in kitchen gardens, vineyards, orchards, field edges, irrigation systems; and near habitation. Persistent noxious weed. Control measures: stubbling, deep plowing, inter-row cultivation during germination period, chemical weeding.Reference citations:
Anon. 1996. Weeds in sugar beet. Berlin: Hoehst Schering AgrEvo GmbH. 114 pp.Nikitin V.V. 1983. Weed plants in the flora of the USSR. Leningrad: Nauka. 168-170 pp. (in Russian)
Shishkin, B.K. 1936. Flora of the USSR. Moscow-Leningrad: Ac. Sc. USSR. V.6: 362 (In Russian)
Veselovskiy I.V., Lysenko A.K., Man'ko Yu.P. 1988. The atlas identification book on weeds. Kiev: Urozhay. 32 pp.(In Russian)