Annual herb with rhizomes and runners, tufted 10 - 40 cm tall Leaves: two to six, basal, alternate, 8 - 12 cm long, 1 - 2 mm wide, flat or V-shaped in cross-section, linear, parallel-veined, keeled beneath, with a sheathing base that encloses the stem. Inflorescence: consisting of terminal spikelet heads, subtended by spirally arranged leafy bracts. Bracts three to six, upright to ascending, unequal, 3 - 12 cm long, 1 - 2.5 mm wide, all or some much longer than the inflorescence, flat or V-shaped in cross-section. Rays (branches of inflorescence) one to three, 0.5 - 2 cm long. Spikelet heads 7 - 15 mm in diameter, hemispheric, dense, consisting of 25 to 50 spikelets. Flowers: minute, in the axil of a floral scale, lacking sepals and petals. Stamen one. Anthers about 0.5 mm long. Pistil one. Style two- or three-cleft. Fruit: a one-seeded achene, short-stalked, brown, about 1 mm long and 0.5 mm wide, broadly ellipsoid with a pointed apex and slender beak, contracted at base, bumpy. Seed with a thin, non-adherent wall. Culm: 10 - 40 cm long, 0.5 - 1 mm wide, roundly triangular in cross-section, solid. Spikelets: 3 - 7 mm long, 2 - 3 mm wide, strongly flattened, egg-shaped, subtended by two small bracts, with eight to twenty floral scales. Scales two-ranked, 1 - 2 mm long, 1 - 1.5 mm wide, egg- lance-shaped with a recurved-pointed apex, two-keeled basally, three-ribbed, lowest one empty.
Similar species: No information at this time.
Flowering: August to mid-September
Habitat and ecology: Rare in the Chicago Region. Found in ditches, mud flats, and other wet places.
Occurence in the Chicago region: native
Etymology: Cyperus is the ancient Greek word for sedge. Acuminatus means "tapering into a long point."
Tufted annual 0.5-4 dm; lvs few, all near the base, slender and ±elongate, 1-2(-3) mm wide; invol bracts 3-6, unequal, elongate, some or all much surpassing the infl;
spikelets 3-7 mm, strongly flattened, 8-20(-40)-fld, borne in very dense, globose clusters on very short axes; scales 1.3-2 mm, ovate, bicarinate basally, strongly 3-nerved, otherwise subhyaline and cellular-reticulate, shortly recurved-acuminate at the tip; rachilla persistent, wingless; stamen 1; anthers 0.5-0.7 mm; achenes rather broadly trigonous, 0.6-1 mm. Streambanks and other wet, low places, tolerant of alkali; Ill. to N.D., Mo., Tex., and n. Mex., e. occasionally to O., Ky. and w. N.C., and w. irregularly to the Pacific.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.