Herbs, perennial, cespitose, 2.5--6.5 dm. Culms erect, terete, 1--3 mm diam., smooth. Cataphylls 0--1, maroon or dark green, apex obtuse. Leaves: basal 1, cauline 2--3; auricles 1--2.1 mm, apex rounded, membranaceous; blade maroon or dark green, terete to compressed, 3--20 cm x 1--2.4 mm. Inflorescences terminal panicles of 30--70(--130), 5--20 cm, branches spreading; primary bract erect; ; heads (1--)2--10-flowered, hemispheric or narrower, 5--10 mm diam. Flowers: tepals green to straw-colored, lanceolate, apex acute; outer tepals (2--)2.6--3.2 mm; inner tepals (1.8--)2.3--3 mm; stamens 3, anthers 1/2--2/3 filament length. Capsules exserted, , straw-colored, 1-locular, linear-lanceoloid, 4--5.2 mm, apex acute, valves separating at dehiscence. Seeds oblong-ellipsoid, 0.3--0.4 mm, not tailed; body clear yellow-brown. Fruiting summer. In soft mucky substrates, marshy shores, sloughs, occasionally in wet wooded places, often in shallow water; commonly abundantly colonizing wet, sandy- alluvial outwash in ditches and clearings; 10--1000 m; Ala., Ark., Calif., Conn., Fla., Ga., Ill., Ind., Kans., Ky., La., Md., Miss., Mo., N.C., Ohio, Okla., S.C., Tenn., Tex., Va., Wash., W.Va.; probably introduced, South America.
From Flora of Indiana (1940) by Charles C. Deam
Common in southern Indiana, especially in the unglaciated area, in roadside ditches, low fallow fields (mostly in hard white clay soil), swampy open woods, and along the banks of or on gravel bars in creeks.
Stems clustered, slender, erect, 2-5 dm, with usually 2-4 terete, septate lvs; infl decompound, very diffusely branched, widely spreading, 1-2 dm, usually constituting a third of the height of the plant, bearing very many obpyramidal, 3-10-fld heads; fls eprophyllate; tep subequal, linear-subulate, 2.3-2.8 mm; stamens 3; fr unilocular, golden-brown, prismatically linear-trigonous or subtriquetrous, 4-6 mm, a fifth as thick, gradually attenuate, very acute, much surpassing the tep. Wet soil and muddy shores; s. Ind. to Mo. and Okla., s. to Ala. and Tex.; coastal plain from se. Va. to S.C.; reported from W.Va.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.