Stems stout, 3–15 dm, arising singly or few together from long, coarse, deep-seated rhizomes, aphyllopodic, the lower sheaths soon breaking and becoming fibrillose; sheaths villous-hirsute all around, or sometimes only toward the ventral summit; blades elongate, 4–10 mm, usually hirsute beneath toward the base, tending to be septate-nodulose; bracts subtending the pistillate spikes sheathless or nearly so, but with elongate blade; spikes several, sessile or inconspicuously short-pedunculate, the lower pistillate and the upper staminate, or the middle one(s) androgynous; staminate spikes 2–6 cm, pale, commonly stramineous, the scales short-awned; pistillate spikes cylindric, 2–10 × 1 cm, the scales stramineous or pale greenish and often largely scarious, narrow, tipped by a rough awn 1–5(–9) mm; perigynia crowded, ascending, pale greenish to stramineous, conspicuously 12–20-ribbed, glabrous, firm, 7–10 mm, lanceolate or lance-ovate, somewhat turgid-inflated below, more flattened toward the well developed beak, this with prominent, often divergent teeth 1.5–2.5(–3) mm; achene trigonous, loosely filling the lower part of the perigynium, continuous with the straight bony style; 2n=74. Marshes and shallow water; circumboreal, extending s. in Amer. to N.Y., W.Va., Mo., Colo., Utah, and Oreg.
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Culms hollow, ± spongy near base, trigonous in cross section, 35–125 cm; vegetative culms hollow, flattened when pressed, taller than fertile culms. Leaves: basal sheaths reddish purple, inner bands fibrillose with age; sheaths with apex of inner band pale brown to dull reddish purple, pubescent or scabrous, at least apically, rarely glabrous; ligules (6–)11–45 mm; blades 3–10 mm wide, usually sparsely to moderately long-pubescent, finely papillose abaxially, glabrous adaxially. Inflorescences 12–60 cm; spikes erect or ascending; proximal 2–5 spikes pistillate; terminal (1–)2–6 spikes staminate. Pistillate scales lanceolate to narrowly ovate, apex acute, conspicuously scabrous-awned, glabrous or scabrous near midrib. Staminate scales lanceolate to narrowly ovate, apex obtuse to acuminate, scabrous-awned, glabrous or, rarely, sparsely pubescent. Perigynia 12–21-veined, (6.5–)7–12 × 1.8–3.8 mm, glabrous; beak 2.1–4 mm, glabrous (rarely few spreading hairs on main veins), teeth spreading to outcurved, (1.2–)1.5–3 mm.
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