Polygonum oxyspermum

Plants green to blue-green, homophyllous. Stems prostrate to ascending, branched at proximal and middle nodes, not wiry, 20-100 cm. Leaves: ocrea 6.5-12 mm, proximal part cylindric, pruinose, distal part hyaline, soon disintegrating into brown fibers or nearly completely deciduous; petiole 0-1 mm; blade green to bluish green, elliptic-lanceolate to linear, 10-35 × 1.5-15 mm, margins flat or narrowly revolute, apex acute; middle stem leaves slightly larger than adjacent branch leaves, distal leaves overtopping flowers. Inflorescences axillary, cymes uniformly distributed, 2-7-flowered. Pedicels exserted from ocreae, 2.5-5(-7) mm. Flowers semi-open; perianth 3.5-5.5 mm; tube 28-39% of perianth length; tepals slightly overlapping, green, margins white to pink, petaloid, not keeled, oblong to obovate, not cucullate; veins branched; stamens 8. Achenes exserted from perianth, pale brown to dark brown, ovate, 3-gonous, (3.5-)4.1-5.5(-6.5) mm, faces subequal, apex not beaked, edges straight, shiny, smooth or with fine tubercles especially toward apex; late-season achenes unknown.

The treatment by D. A. Webb and A. O. Chater (1963) of the Polygonum oxyspermum complex is followed here. T. Karlsson (2000) accepted P. raii and P. oxyspermum as distinct species.

Much like no. 5 [Polygonum glaucum Nutt.], often greener; ocreae to 5(-7) mm, brown, 3-7-nerved, lacerate; mature perianth 3-5 mm; achenes 3.5-5 mm (to 6.5 mm in late fls); 2n=40. Damp beaches; Atlantic coast from N.S. and N.B. to Nf., and in nw. Europe, perhaps only intr. in Amer. (P. acadiense; P. raii)

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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