Annual herb with red roots, tufted 5 cm - 0.5 m tall Leaves: basal, alternate, 5 - 25 cm long, 2 - 9 mm wide, flat or inversely W-shaped in cross-section, linear, parallel-veined, keeled beneath, with a sheathing base that encloses the stem. Inflorescence: consisting of one to three terminal spikes, subtended by spirally arranged leafy bracts. Bracts five to seven, horizontal to ascending, unequal, 10 - 20 cm long, 1 - 3 mm wide, inversely W-shaped in cross-section. Rays (branches of inflorescence) two to six, 1 - 8 cm long. Spikes some stalkless, 1 - 4 cm long, 1 - 1.5 cm wide, densely cylindrical to egg-shaped, consisting of 40 to 80 spikelets. Flowers: minute, in the axil of a floral scale, lacking sepals and petals. Stamens exserted. Anthers under 0.5 mm long. Pistil one. Style over 0.5 mm long. Fruit: a one-seeded achene, stalkless, white to light gray to brownish, about 1 mm long and 0.5 mm wide, egg-shaped with a rounded apex bearing a tiny point, unequally three-angled. Seed with a thin, non-adherent wall. Culm: 5 cm - 0.5 m long, 1 - 2.5 mm wide, triangular to roundly triangular in cross-section, solid. Spikelets: 3 - 12 mm long, 1 - 1.5 mm wide, linear, four-angled, subtended by two small bracts, with six to sixteen floral scales. Scales appressed, greenish down the middle, light brown and reddish-speckled along the sides, about 1.5 mm long and 1 mm wide, oblong egg-shaped to reverse egg-shaped with a rounded apex bearing a tiny point, four-angled to nearly circular in cross-section, three-ribbed down the middle, lowest one empty.
Similar species: No information at this time.
Flowering: late July to late September
Habitat and ecology: Frequent along shores and ditches, often in alkaline areas.
Occurence in the Chicago region: native
Etymology: Cyperus is the ancient Greek word for sedge. Erythrorhizos means "with red roots."
Stout, tufted annual 1-7 dm with red roots; lvs crowded toward the base, with elongate blade 2-9 mm wide; invol bracts several, elongate, unequal; infl of clustered, cylindric spikes, the terminal cluster sessile, the others on rays to 7 cm, each spike 1-4 cm, with numerous serially arranged spikelets on an elongate rachis; spikelets 3-12 נ1-1.5 mm, 6-many-fld; rachilla persistent, with narrow, deciduous, hyaline wings; scales 1.2-1.5 mm, ovate to elliptic, with prominent, green, minutely excurrent keel, 1 or 2 adjacent pairs of much finer lateral nerves, and narrow, golden- brown margins; achenes pearly-white, unequally trigonous, 0.7-1 mm; 2n=96. Streambanks and other wet places; Mass., N.H., and N.Y. to Ont. and N.D., s. to Ark., Tex., and Ariz., and 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.