Plants perennial, cespitose, 80-150 cm; rhizomes absent. Culms excurved nodding, leafy, triangular, slender; principal leaves overtopped by culm; blades flat, 2.5-5 mm wide, apex attenuate, trigonous. Inflorescences terminal and axillary, spikelet clusters mostly 2-6, compact, turbinate to hemispheric, 1.5-2 cm wide; peduncles progressively shorter distally on culm; bracteal leaves mostly exceeding subtended groups. Spikelets crowded, deep red brown, lance ellipsoid, 4.5-6.5 mm; fertile scales ovate lanceolate, 3.5-4(-4.5) mm, apex acute, midrib mostly short excurrent. Flowers: perianth bristles 6, overtopping tubercle, antrorsely barbellate. Fruits (1-)2(-3) per spikelet, 3-4 mm; body dark red brown with pale center, stipitate, lenticular, obovoid, or orbicular, 1.5-2 × 1.2-1.4 mm, base narrowed, margins pale, wirelike; surfaces slick; tubercle triangular-subulate, 1.3-1.5(-1.8) mm. Fruiting summer-fall. Moist to wet meadows, swales, fens, flatwoods, and bogs, 0-500 m; Ala., Ark., Del., Fla., Ga., Ill., Ky., La., Md., Miss., N.J., N.C., Okla., S.C., Tenn., Tex., Va., W.Va. Rhynchospora glomerata is often associated with R. capitellata and is distinguishable by its taller, slightly stouter habit; longer, slightly paler spikelets; and longer and broader fruit body. It is a common lowland weed in the southern Piedmont, Atlantic coastal plain, and Gulf coastal plain, where it is often more associated with R. inexpansa.
Much like no. 11 [Rhynchospora capitellata (Michx.) Vahl; lvs to 5 mm wide; frs (1)2-3; bristles 3.2-3.7 mm, equalizing or surpassing the tubercle; achenes with an evident pale umbo and heavy, wire-like raised margin; tubercle 1.3-1.8 mm. Bogs and wet sand; Fla. to Tex., n. on the coastal plain to N.J. and inland to Ky. and Ark.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.