Annual herb with fibrous roots, tufted 1 - 25 cm tall Leaves: alternate, 5 - 20 cm long (often equal to culm), 1.5 - 3 mm wide, flat, 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 one to four, more or less horizontal, unequal, 1.5 - 15 cm long, 1.5 - 3 mm wide, flat. Rays (branches of inflorescence) one to six, 1 - 6 cm long, unequal. Spikelet heads 1 - 2 cm in diameter, more or less palmate, consisting of six to twelve spikelets. Flowers: minute, in the axil of a floral scale, lacking sepals and petals. Stamens two (sometimes three), exserted. Anthers under 0.5 mm long. Pistil one. Style to 0.5 mm long, two-cleft nearly to the base. Stigma 2 - 3 mm long. Fruit: a one-seeded achene, short-stalked or stalkless, brown, about 1 mm long and 0.5 mm wide, lenticular (lens-shaped) and egg-shaped or reverse egg-shaped with a small, slender point at the apex, tiny-dotted, with a network of ridges. Seed with a thin, non-adherent wall. Culm: 1 - 25 cm long, triangular in cross-section, solid. Spikelets: 0.5 - 1.5 cm long, 2 - 3.5 mm wide, compressed, oblong lance-shaped, subtended by two small bracts, with eight to twenty-eight floral scales. Scales spirally arranged and overlapping, straw-colored to light brown or colorless with a red marginal band, 2.5 - 3 mm long, about 2 mm wide, egg-shaped, lowest one empty.
Similar species: No information at this time.
Flowering: mid-August to late September
Habitat and ecology: Uncommon. Found along the shores of streams and ponds where inundation has left little sediment remaining.
Occurence in the Chicago region: native
Etymology: Cyperus is the ancient Greek word for sedge. Diandrus means "with two stamens."
Tufted annual (0.5)1-2(-4) dm; cauline lvs often equaling the stem, to 3 mm wide; bracts usually 3, the lowest to 15 cm; rays 1-3, to 6 cm; spikelets 6-10, 8-15 נ2-3.5 mm; scales ovate, 2.5-3 mm, as seen from the side in half-view over 3 times as long as wide and obscurely acuminate, at maturity red-purple at the tip and in a tapering marginal band almost or quite to the base that is separated from the midrib by a colorless furrowed strip; stamens 2 (or 3 in upper fls); achenes lenticular, elliptic- obovate, 1-1.3 mm; style cleft almost to the base, persistent. Wet ground, especially along shores; Me. and Que. to N.D., s. to Va. and Io.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.