13. Polygonum argyrocoleon Steudel ex Kunze, Linnaea. 20: 17. 1847.
Persian or silversheath knotweed
Plants green, heterophyllous. Stems erect or decumbent, branched mostly from base, not wiry, 15-100 cm. Leaves: ocrea 4-8 mm, proximal part cylindric, distal part soon disintegrating into curly or straight fibers; petiole 0-1.5 mm; blade bluish green, lanceolate or linear-lanceolate, 15-50 × 2-8 mm, margins flat, apex acute; stem leaves 2.1-4 times as long as branch leaves; distal leaves abruptly reduced and not overtopping flowers (shorter than or equaling flowers). Inflorescence axillary and terminal, spikelike; cymes aggregated at tips of stems and branches, 4-6-flowered, bracts inconspicuous. Pedicels enclosed in ocreae, 1-2 mm. Flowers closed; perianth 1.8-2.4 mm; tube 10-22% of perianth length; tepals overlapping, green or white, usually with pink, rarely red or white, margins, petaloid, not keeled, oblong to obovate, cucullate; midveins usually unbranched; stamens 7-8. Achenes enclosed in perianth, brown, ovate, 3-gonous, 1.3-2.3 mm, faces subequal, slightly concave, apex not beaked, with concave edges, shiny, smooth; late-season achenes unknown.
Flowering May-Oct. Fields, gardens, disturbed sites, often in saline soils; 0-1200 m; introduced; Ariz., Calif., Colo., Fla., Idaho, La., Mass., Mo., Nev., N.Mex., N.C., Tex., Utah, Vt., W.Va.; c Asia.