12. Polygonum patulum M. Bieberstein, Fl. Taur.-Caucas. 1: 304. 1808.
Plants green or bluish green, heterophyllous. Stems mostly ascending or erect, branched from base, not wiry, 20-80 cm. Leaves: ocrea 7-9 mm, proximal part cylindic, distal part disintegrating into straight fibers; petiole 0.2-1 mm; blade green or bluish green, linear to lanceolate, 25-40 × 4-8 mm, margins flat, apex acute; stem leaves 2-4 times as long as branch leaves; distal leaves abruptly reduced and not overtopping flowers (shorter than or equaling flowers). Inflorescences axillary and terminal, spikelike; cymes aggregated at tips of stems and branches, 1-3-flowered. Pedicels enclosed in ocreae, 1.5-2 mm. Flowers closed or semi-open; perianth 2.2-3 mm; tube 15-30% of perianth length; tepals overlapping, green with white to pink margins, petaloid, not keeled, oblong, cucullate; veins branched; stamens 8. Achenes slightly exserted from perianth, light brown to dark brown, ovate, 3-gonous, 2-2.3(-2.8) mm, faces subequal, concave, apex not beaked, edges concave, dull, striate-tubercled; late-season achenes uncommon, 2.5-4 mm.
Flowering Jul-Oct. Waste places; 0-800 m; introduced; Ala., Ill., Wash.; Eurasia; n Africa.
The name Polygonum patulum has been misapplied to a distinctive form of P. ramosissimum in saline marshes in California (M. Costea and F. J. Tardif 2003b).