Plants aggregated in dense tussocks; rhizomes branching, short, tough, fibrous. Culms: fertile ones upright or nearly so; nodes without axillary bulblets. Leaves 5-10 per culm; sheaths of proximal leaves green to red-brown; proximal sheaths and blades with septa few to many, conspiucuous or inconspicuous; blades 22-80 cm × 3-10 mm. Inflorescences terminal; rays ascending or sometimes spreading, scabrous throughout or main branches smooth proximally, rays without axillary bulblets; bases of involucral bracts reddish brown, brownish, or blackish, not glutinous. Spikelets in dense cymes of 2-15, central spikelet of each cyme sessile, others sessile or pedicellate, spikelets broadly ovoid, ovoid, or sometimes cylindric, 3.5-8 × 2.5-3.5 mm; scales reddish brown, brownish, or blackish, ovate or narrowly ovate to oblong-ovate or oblong-elliptic, 1.1-2.2 mm, apex apiculate or short-mucronate, apiculus or mucro to 0.1 mm. Flowers: perianth bristles persistent, 6, slender, contorted, much longer than achene, smooth, projecting beyond scales, mature inflorescence appearing woolly; styles 3-fid. Achenes whitish to very pale brown, elliptic or obovate in outline, plumply trigonous or plano-convex, 0.6-0.9 × 0.3-0.5 mm. 2n = 66. Fruiting late summer-early fall (Aug-Sep, earlier in s United States). Marshes, moist meadows, ditches, shallow ponds, frequently growing in disturbed areas; 0-800 m; Man., N.B., Nfld. and Labr., N.S., Ont., P.E.I., Que.; Ala., Ark., Calif., Conn., Del., Fla., Ga., Ill., Ind., Iowa, Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., N.H., N.J., N.Y., N.C., Ohio, Okla., Oreg., Pa., R.I., S.C., Tenn., Tex., Vt., Va., Wash., W.Va., Wis., Wyo.; Mexico. Scirpus cyperinus is extremely variable. A form common in the northern part of its range, south to Iowa, northern Ohio, Maryland, and (in the Appalachians) North Carolina and Tennessee, has bases of the involucral bracts and the involucels blackish, the spikelets sessile or nearly so in glomerules, and the scales relatively short, ovate, and brownish. This form has often been treated as S. cyperinus var. pelius. A more robust southern form, extending north to southern Missouri and Illinois, Kentucky, Virginia, and (along the coast) New Jersey and Massachusetts, has the bases of the involucral bracts and the involucels reddish brown, the spikelets mostly solitary, and the scales relatively long, narrowly elliptic, and reddish brown. This form has often been treated as a distinct species, S. rubricosus (or under the illegitimate name S. eriophorum Michaux). These two morphologies intergrade so extensively that it is not practical to recognize them taxonomically at any rank. Scirpus cyperinus often hybridizes with S. atrocinctus and S. pedicellatus, forming hybrid swarms. Some plants appear to have characteristics of all three species; the names Scirpus atrocinctus var. grandis Fernald and S. atrocinctus forma grandis (Fernald) D. S. Carpenter are based on such a specimen.
Perennial herb with short, tough rhizomes, forming dense tussocks to 2 m tall Leaves: three-ranked, five to ten per culm. Sheaths of lower leaves green to reddish brown. Blades 22 cm - 0.8 m long, 3 - 10 mm wide, keeled beneath. Inflorescence: a large, terminal arrangement of spikelets with ascending or spreading branches, subtended by three leaf-like bracts. Bracts reddish brown to blackish basally. Flowers: minute, subtended by a floral scale, lacking sepals and petals, bearing six persistent bristles. Bristles slender, contorted, much longer than achene, growing past the scales (giving the mature spikelets a woolly appearance). Stamens one to three, exserted. Pistil one. Style linear, three-cleft, base persistent. Fruit: a one-seeded achene, light brown to whitish, 0.5 - 1 mm long, to 0.5 mm wide, reverse egg-shaped, short-beaked, plumply three-sided or flat on one side and convex on the other, minutely bumpy. Culm: to 2 m long, three-sided, solid. Spikelets: in dense clusters of two to fifteen, mostly stalkless (only one or two are stalked within each cluster), 3 - 8 mm long, 2.5 - 3.5 mm wide, broadly egg-shaped to egg-shaped or sometimes cylindrical. Floral scales spirally arranged, brown to reddish brown or blackish, 1 - 2 mm long, narrowly egg-shaped to egg-shaped to oblong egg-shaped or oblong and elliptic, abruptly short-pointed or bearing a short, tiny point at the apex.
Similar species: No information at this time.
Flowering: late June to mid-September
Habitat and ecology: Locally abundant in moist flats, marshy ground, and boggy areas. Also found in dried-up swamps where competition is much reduced.
Occurence in the Chicago region: native
Etymology: Scirpus comes from the Latin name for a bulrush. Cyperinus means "resembling Cyperus (the genus)."
Cespitose perennial, forming dense tussocks on short tough rhizomes; stems to 2 m; principal blades 3-10 mm wide; bracts lf-like, unequal, spreading, usually drooping at the tip, pigmented at base but not glutinous; rays of the infl several, ascending below, ±divaricate above, branched and involucellate toward the tip, the ultimate branches with 1-several sessile spikelets and often 1 or 2 pedicellate spikelets; spikelets ovoid to cylindric, 3-5(-10) mm; scales elliptic or oval, 1-2 mm, obtuse and mucronulate to broadly acute, marked (at high magnification) with numerous fine red lines; bristles 6, smooth, contorted, evidently surpassing the scales and giving the mature spikelets a woolly look; style trifid; achene pale yellowish-gray to nearly white, obovate, compressed-trigonous, 0.7-1 mm, sharply short-beaked; 2n=60, 64, 66, 68, 70. Bogs, marshes, and wet meadows; Nf. to B.C., s. to Fla. and Tex. Fr June-Sept. Highly variable, consisting of several geographically and ecologically widely overlapping phases that intergrade freely without wholly losing their identity. (S. atrocinctus, mainly northern, and extending w. to B.C., in meadows, with pedicellate spikelets, blackish scales, and early fr; S. pedicellatus, northern but not western, in alluvial marshes, with pedicellate spikelets, pale brown scales, and late fr. (S. eriophorum; S. rubricosus) Putative hybrids with no. 24 [Scirpus atrovirens Willd.] have been called S. ذeckii Britton.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.