Culms 10-75 cm. Leaves 3-5 per culm; sheaths tight, inner band hyaline, 4-13 cm, apex concave, glabrous; ligules 0.3-1.7 mm, rounded to obtuse; blades plicate, 7.5-25 cm × 1.2-2.6 mm, widest leaf 1.6-2.6 mm wide. Inflorescences densely crowded distally, often with basal spikes ± separate, 0.9-4 cm; spikes 3-8; unisexual with pistillate and staminate spikes on different plants; pistillate plants rarely with few staminate flowers; staminate plants sometimes with few pistillate flowers scattered on spikes or, occasionally, entirely pistillate spikes mixed with entirely staminate ones in same inflorescence; proximal 2 spikes 3.8-15.5 mm apart, lateral spikes 3-13.5 mm, similar to terminal spikes; terminal spikes 3.5-13.7 mm, usually unisexual, pistillate spikes 5-26-flowered, 4.5-7.2 mm wide, staminate spikes 6-31-flowered, 1.2-2.6 mm wide. Pistillate scales ovate, 1.8-2.9 × 1-1.8 mm, apex acute. Staminate scales ovate, 2.2-3.3 × 1.1-1.8 mm, base not clavate, apex acute. Anthers (1-)1.2-2.2(-2.35) mm. Perigynia spreading to reflexed, castaneous to almost black, 5-12-veined abaxially, 0-10-veined adaxially, ovate to deltate, 2.1-3.8 × 1.2-2.2 mm, 1.4-2.3(-2.7) times as long as wide; beak 0.65-1.6 mm, 0.45-0.8 length of body, setulose-serrulate, teeth whitish, 0.15-0.5 mm, soft. Achenes ovate to suborbiculate, 1-1.7 × 0.9-1.3 mm.
Fruiting late spring-early summer. Fens, openings in white-cedar swamps, wet calcareous prairies, fresh interdunal meadows, calcareous seeps, lake and river shores, wet sunny limestone outcrops; 0-800 m; Man., Nfld. and Labr. (Nfld.), Nunavut, Ont., Que., Sask.; Conn., Ill., Ind., Iowa, Maine, Mass., Mich., Minn., Mo., N.J., N.Y., Ohio, Pa., Tenn., Va., W.Va., Wis.
Stems tufted, aphyllopodic, 1-7 dm, stiff, scabrous on the angles above; lvs 3-5 per stem, all in the basal third, shorter than the stems, plicate, 1-2.5 mm wide, scabrous above; spikes 3-8, 3-13 mm, sessile, all crowded or the lower remote; subdioecious, occasionally with a few intermingled or basal fls of opposite sex, rarely with staminate and pistillate spikes in the same infl; anthers 1.2-2.2 mm; pistillate scales castaneous with green midrib and hyaline margins; perigynia 5-25, at least the lower ones spreading to reflexed, castaneous, planoconvex, ovate to deltoid, spongy-thickened at base, 2.1-3.8 mm, two-fifths to two-thirds as wide, 5-12-nerved on both sides or nerveless ventrally, serrulate distally and on the prominent, softy bidentate beak 0.6-1.6 mm; achene lenticular. Calciphile, in wet places; Nf. to Sask., s. to Pa., W.Va., Tenn., Ill., and Mo. (C. muricata var. s.; C. elachycarpa)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.