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.