Bull. Torrey Bot. Club 81: 33. 1954.
Rhizomes 5–15 mm diam. Culms cylindric, 1–4 m × 2–10 mm. Leaves 3–4, all basal; sheaths often dark reddish proximally, front membranous-translucent and splitting, orifice adaxially deeply V-shaped; blades 1–2, C-shaped to dorsiventrally flat in cross-section, usually much shorter than sheath, distal blade 8–120 × 3–7 mm, margins often scabridulous. Inflorescences 2 (–3) times branched, open or compact, branches 6 (–18) cm; proximal bract usually erect, thickly C-shaped in cross-section, 1–9 cm, margins sometimes scabridulous. Spikelets 3–190, solitary or in clusters of 2–8, never all solitary; scales reddish to orangebrown to straw-colored, often variable on same scale, usually wholly or partly straw-colored and prominently lineolate-spotted at 10X, scale or midrib often green when young, ovate, 3–4 × 2–3 mm, sparsely to often densely reddish or straw-colored spinulose-papillose distally or on most of surface, margins ciliate, hairs long, contorted, flanks veinless, apex acute to obtuse, notch 0.3–0.5 mm deep, awn on at least some scales in spikelet usually strongly contorted, 0.5–2 mm (often broken off). Flowers: perianth members (4–) 6 (–8), brown, bristlelike, equaling achene body or sometimes much shorter, rarely rudimentary, spinulose; anthers 2 mm; styles 2 (–3) -fid. Achenes dark graybrown, planoconvex or rarely weakly trigonous, obovoid, (1.5–) 2–3 1.2–1.7 mm; beak 0.2–0.4 mm.
Alta., B.C., Man., N.B., N.S., N.W.T., Ont., P.E.I., Que., Sask., Yukon, Alaska, Ariz., Ark., Calif., Colo., Conn., Del., Idaho, Ill., Ind., Iowa, Kans., Ky., Maine, Mass., Md., Mich., Minn., Mo., Mont., N.C., N.Dak., N.H., N.J., N.Mex., N.Y., Nebr., Nev., Ohio, Okla., Oreg., Pa., R.I., S.Dak., Tex., Utah, Va., Vt., Wash., Wis., Wyo., Mexico, possibly Eurasia, e Pacific Islands
Varieties 2 (2 in the flora).
Plants of Schoenoplectus acutus var. occidentalis that have most styles 3-fid, most achenes trigonous, and culms very soft with large air cavities occur at lower elevations in California (mostly southern) and Baja California. In California they often grow on stream bars. They may deserve varietal status. The varieties intergrade throughout most of the west with var. occidentalis.
Schoenoplectus acutus hybridizes with Schoenoplectus tabernaemontani, S. heterochaetus, and S. californicus (see also S. tabernaemontani).
Although previously assumed to be restricted to North America, some specimens from Eurasia are probably Schoenoplectus acutus, and one very young specimen from Clipperton Island in the eastern Pacific is probably S. acutus var. occidentalis.
|1||Styles 2-fid; achenes plano-convex; culms mostly very firm, air cavities in distal 1/4 mostly ca. 0.5 mm wide.||Schoenoplectus acutus var. acutus|
|1||Some styles 3-fid; some achenes compressed, obtusely trigonous; culms firm to soft, larger air cavities in distal 1/4 1–2.5 mm wide.||Schoenoplectus acutus var. occidentalis|
"prolonged" is not a number.