Plants colonial; rhizomes long-creeping. Culms central, coarse, trigonous, 55-130 cm, scabrous-angled. Leaves: basal sheaths pale green to brownish or red tinged; ligules 5-14 mm; blades glaucous, M-shaped, (4.5-)5.5-12(-20) mm wide, glabrous. Inflorescences 15-35 cm; proximal 2-5 spikes pistillate, ascending; distal spikes erect; terminal 1-2(-3) spikes staminate. Pistillate scales lanceolate, acute to acuminate, glabrous, at least the proximal with scabrous awn to 3.5 mm. Perigynia ascending, ± glaucous, often strongly red dotted, ± strongly 12-18-veined, thin-walled, narrowly ovoid, flattened-trigonous, 3-4.5 × 1.4-2.1 mm, glabrous; beak 0.3-0.6 mm, emarginate to weakly bidentulate, teeth to 0.2 mm. 2n = 78. Fruiting Jun-Aug. Open swamps, wet, open thickets, marsh edges, sedge meadows, lakeshores; 0-300 m; introduced; Ont.; Conn., Ind., Mass., Md., Mich., N.Y.; Eurasia; Africa. An uncommon and local introduction, Carex acutiformis forms large, glaucous clones where it is established but is, as yet, not spreading aggressivly into adjacent habitats. It superficially resembles C. aquatilis, but is larger, has 3 stigmas, and has strongly veined perigynia 3-4.5 mm.
Stems stout, 5-15 dm, arising singly or few together from long, stout, scaly rhizomes, aphyllopodic, but clothed at the base with the dried-up lf-bases of the previous year; lower sheaths soon breaking and becoming fibrillose; main lvs 5-8 mm wide; ligule about as long as wide; staminate spikes 2-4; pistillate spikes 2-5, widely separate, cylindric, 3-8 cm נ7 mm, densely fld, erect, sessile or short-peduncled; bracts sheathless or nearly so, the lowest one elongate and lf-like, the upper much reduced; pistillate scales lanceolate, to about as long as the perigynia, acute to acuminate or short- awned; perigynia broadly and obtusely ovoid-trigonous, glabrous but dull, with numerous ±evidently raised nerves, 2.5-4.5 mm, narrowed to a short beak with obscure triangular teeth wider than long; achene trigonous, continuous with the short, straight, slender style; 2n=38, 78. Native of Eurasia and Afr., intr. in wet meadows here and there in our range, as in Mass. and Ind.
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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