Cyperus rotundus L.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Perennial with numerous slender rhizomes ending in small tubers; stems 2–5 dm, smooth; lvs basally disposed, mostly shorter than the stem, 3–6 mm wide; bracts few, all or all but one shorter than the infl; rays 3–7, simple or sometimes branched at the top, to 10 cm; spikelets 3–10 in short-cylindric spikes, 10–40-fld, to 4 cm; scales closely imbricate, ovate, 2.5–3.5 mm, obtuse, keeled, 7-nerved (3 in the midvein, 2 nearby on each side), the sides purple-brown or red- brown; rachilla persistent, winged; achenes nearly black, narrowly trigonous-obovoid, 1.5 mm; 2n=108. A weed of sandy soil; pantrop., n. to Va. and Ky., and occasionally adventive farther n.