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.
From Flora of Indiana (1940) by Charles C. Deam
Frequent on marshy banks of streams and occasional in open swamps, bogs, and springy places in woods. Not known from the unglaciated area.
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.