Sp. Pl. 4(1): 208. 1805.
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.
Phenology: Fruiting late spring–early summer.
Habitat: Fens, openings in white-cedar swamps, wet calcareous prairies, fresh interdunal meadows, calcareous seeps, lake and river shores, wet sunny limestone outcrops
Elevation: 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.