Herbs, perennial, cespitose. Culms with cormlike bases, sharply trigonous, 25-90 cm, glabrous proximally, minutely scabridulous distally. Leaves V-shaped, 14-40 cm × 3.5-8 mm, (pubescent on adaxial side of midrib). Inflorescences: spikes loose, obtrulloid to obdeltoid (broadest near apex, nearly as long as wide), 20-28(-34) × (12-)15-30 mm; rays 4-13, (1-)4-24 cm (longest ray shorter than bracts), glabrous; bracts 3-12, ascending at 30-45°, flat, 3-25 cm × 3-7 mm; rachilla persistent, wings 0.4-0.6 mm wide, covering 3/4 of mature achene. Spikelets 30-50, proximal one reflexed, distal ones divaricate, linear-lanceoloid, ± terete, (6.5-) 8-10(-17) × 0.5-0.7 mm; floral scales persistent, 3-6(-8), appressed, stramineous (suffused with reddish purple), 4-5-ribbed laterally, ovate-lanceolate, (4-)4.4-4.9(-5.4) × 1.3-1.5 mm; terminal scale not spinose, apex straight, excurved mucronate, or cuspidate. Flowers: anthers 0.7-1.2 mm; styles 1.5-2 mm; stigmas 2-2.5 mm. Achenes brown to brownish black, narrowly oblong, (2.2-)2.5-3 × 0.6-0.7 mm, base cuneate, apex obtuse, apiculate, surfaces puncticulate. Fruiting summer. Roadsides, pastures, disturbed sites in sandy or clayey soils; 0-300 m; Ala., Ark., Del., D.C., Ga., Ky., Mo., N.J., N.C., Ohio, Pa., S.C., Tenn., Va. For information concerning nomenclature of Cyperus retrofractus, see J. R. Carter and C. E. Jarvis (1986).
Tufted perennial, the cormose stem-bases joined by short rhizomes; stems rigid, 3-9 dm, acutely trigonous, antrorsely scabrous above, often smooth near the base; lvs 4-8, 3.5-8 mm wide, minutely rough-puberulent across the surface beneath and on the midrib above; bracts 3-12, the longest one at least as long as the longest ray; rays 4-13, glabrous, the longest 1-2 dm; prophylls smooth to ciliate; spikes obovoid or shortly obconic, 2-3 cm, less than twice as long as thick, the axis 10-22 mm; spikelets stramineous or dull greenish, often suffused with anthocyanin, 1-2(-4)-fld, subulate-acuminate, 8-10(-15) mm, crowded, the uppermost widely spreading or recurved, the others reflexed; scales closely appressed, lance-ovate, acute, (4-)4.5-5(-5.5) mm; achenes trigonously oblong, held between the hyaline wings of the rachilla for 3/4 their length. Pastures, roadsides, and other disturbed places; N.J. to Ga., w. to s. O., Mo., and Ark. (C. dipsaciformis)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.