Herbs, perennial, occasionally tufted, sometimes rhizomatous, 3--13 dm. Rhizomes short, knotty. Culms compressed. Leaves basal and cauline; auricles 0.5--1.5 mm, apex rounded, membranous; basal blade flat, 20--4.5 dcm x 1.5--5 mm, cauline reduced. Inflorescences glomerules, (2--)5--200, each with (1--)2--10(--20) flowers, mostly open, 3--10(--15) cm; primary bract shorter than inflorescence. Flowers: tepals dark brownish, usually with green midstripe, outer series ovate-lanceolate, 1.8--3.2 mm, margins broad, clear, awned or not, apex acutish; inner series ovate to lanceolate, 2--3.5 mm, slightly longer than outer series, apex obtuse to acute, awned or not; stamens 3, opposite outer tepals, shorter to longer than tepals, filaments 1.1--2.5 mm, anthers 0.3--1.2 mm; style 0.3 mm. Capsules brown and sometimes dark spotted, 3-locular, obovoid to nearly globose, 1.8--2.9 mm, shorter to longer than perianth. Seeds yellow to light brown, fusiform, 0.4--0.7 mm, not tailed. 2n = 38, 40. Flowering and fruiting late spring--fall. Moist to wet sandy, peaty, or clayey soils, usually in open areas including bogs, shores, marshes, and ditches; N.S., Ont.; Ala., Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Nebr., N.H., N.J., N.Mex., N.Y., N.C., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Vt., Va., W.Va., Wis.; Mexico; West Indies (Cuba); Central America. The number of glomerules per inflorescence, stamen length vs.versus perianth length, and tepal shape have separately and in combination been used to distinguish a number of taxa at various nomenclaturalorial ranks. These characters, however, vary considerably across the distribution of the species (broad sense) and do so independently of one another to the point that if separate taxa are recognized, they pass insensibly among each other.
Stems cespitose, bulbous-thickened at base, 2-5 dm, seldom taller; lf- sheaths with rounded scarious auricles; principal blades 1-3 mm wide, with 3 prominent veins; invol lf shorter to somewhat longer than the infl; heads 5-20, 4-6 mm thick, subtended by lance-attenuate bracts; fls eprophyllate; sep lanceolate, 2.1-3.1 mm, acuminate or short-aristate; pet 2.3-3.3 mm, oblong with broadly scarious margins, obtuse or rounded; stamens 3, nearly as long as the tep, the anthers reddish-brown, much shorter than the filaments, usually soon shriveling; fr incompletely 3-locular (the partitions not meeting in the center), somewhat turgid-inflated, broadly obovoid, 1.8-2.9 mm, nearly or quite as thick, broadly rounded or somewhat retuse at the tip; 2n=38, 40. Wet meadows and swales; N.S. to Minn. and S.D., s. to Fla. and Tex.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.