Plants silvery, homophyllous. Stems prostrate to ascending, branched from base, not wiry, 20-70 cm. Leaves: ocrea persistent, 7-15 mm, proximal part cylin-dric, pruinose, distal parts silvery, margins overlapping, entire or lacerate; petiole 0.5-3 mm; blade bluish green, lanceolate, 10-30 × 2-8 mm, coriaceous, margins revolute, apex obtuse or acute, rugulose when fresh, markedly rugulose when dried, glaucous; middle stem leaves slightly larger than adjacent branch leaves, distal leaves overtopping flowers they subtend. Inflorescences axillary; cymes uniformly distributed, 1-3-flowered. Pedicels enclosed in ocreae, 3-5 mm. Flowers semi-open; perianth (2-)3-4 mm; tube 12-26% of perianth length; tepals ± recurved, overlapping, white, margins white or pink, petaloid, not keeled, oblong-obovate to spatulate, not cucullate; midvein usually unbranched; stamens 8. Achenes exserted from perianth, reddish brown to dark brown, ovate, 3-gonous, 2.5-3(-4) mm, faces subequal, apex not beaked, edges straight, shiny, smooth; late-season achenes common, 3-5 mm. 2n = 40.
Flowering Jul-Nov. Coastal beaches, sand dunes, margins of salt ponds; 0-10 m; Conn., Del., D.C., Fla., Ga., Md., Mass., N.J., N.Y., N.C., R.I., S.C., Va.
Polygonum glaucum is restricted to maritime beaches along the Atlantic coast from Massachusetts south to Georgia. Over most of its range it is rare and declining; populations on coastal islands of Massachusetts and along the shore of Long Island appear to be secure. Seabeach knotweed appears to be related to P. oxyspermum.
Annual to 3(-7) dm, homophyllous, diffusely branched, prostrate or nearly so, commonly with upturned branch-tips, very pale and glaucous; lvs lanceolate or narrowly elliptic, 1-3 cm נ2-8 mm; ocreae conspicuous, mostly 7-10 mm (at least on the lower nodes), silvery-scarious distally, the lower half becoming brown, with 8-16 usually scabrellous nerves; pedicels included in the ocreae; mature perianth 3-4 mm, divided nearly to the base, the lobes loosely spreading, obovate-oblong, obtuse or broadly rounded above, with green midrib and white to pink margins; achene 3-4 mm, exsert, glossy, brown to blackish; 2n=40. Sandy beaches; Mass. to Ga. (P. maritimum, misapplied)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.