Culms trigonous, 15-60 cm, scabrous-angled. Leaves: sheath with apex of inner band yellowish, thickened, concave; ligules 1.5-2.2 mm; blades 1.5-4 mm wide. Inflorescences 2-8 cm; spikes 5-20, ascending, ovate; proximal spikes pistillate, the middle androgynous or staminate; terminal spike usually staminate. Pistillate scales reddish brown with green center and hyaline margins, ovate, 5-7.8 mm, usually longer than perigynia, apex acute to acuminate. Perigynia prominently thin-winged at apex, lanceolate to broadly ovate, (4-)4.5-6 × 1.3-3.3 mm; beak poorly defined, 1.2-2.5 mm. 2n = 58, 60-64, 64. Fruiting May-Jul. Maritime sand dunes and sandy, disturbed areas near the coast, 0-30 m; introduced; Del., Md., N.C., Oreg., Va.; Eurasia. Carex arenaria was first collected in North America in 1870; it remains quite local in distribution.
Stems 1.5-5 dm, scattered on long tough rhizomes, aphyllopodic; lvs thick, 1-3 mm wide; spikes numerous, 5-12 mm, closely aggregated into an oblong head 2-6 cm, usually the lowest bract, and sometimes the others, long-cuspidate; perigynia surpassed by or merely equaling the broadly ovate scales, planoconvex, lance-ovate, multinerved on both sides, 4-5.5 mm, broadly winged above, the conspicuously bidentate beak a third as long as the body; achene lenticular. Native of Europe, intr. in our range on coastal sands from Md. to N.C.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.