Herbs, perennial, stoloniferous; stolons (2-)5-12 cm × 1-2 mm, bearing tubers 3-8(-12) mm diam., wiry, springy when dried, indurate. Culms trigonous, 10-35(-40) cm × 0.7-3.4 mm, basally indurate, glabrous. Leaves V-shaped to flanged V-shaped, 5-30 cm × 2-6 mm. Inflorescences: spikes 1(-3), broadly ellipsoid, (12-)15-25(-30) × (12-)

Fruiting summer-fall. Croplands, disturbed soils usually; 0-400 m; Ala., Ariz., Ark., Calif., Fla., Ga., La., Miss., Mo., N.Mex., N.C., S.C., Tenn., Tex., Va.; Mexico; Central America; South America; Asia; Africa; Australia.

Cyperus rotundus is documented in Connecticut, Delaware, New York, and Pennsylvania; there is no evidence of persistent populations.

Cyperus esculentus and C. rotundus are the only two species of subg. Cyperus in the New World that produce tuberiferous stolons. The two species also have persistent floral scales and persistent rachillas, a combination of characteristics not found in any other New World species of Cyperus.

Cyperus rotundus is distinguished from other species of the genus in the New World by its open spikes composed of linear reddish spikelets borne on a conspicuous slender rachis. Cyperus rotundus is usually acknowledged to be the world´s worst weed (cf. G. C. Tucker 1987). In the United States, it does not grow north of the mean 1°C January isotherm. Cyperus esculentus (preceding species) is a serious weed in much of the world, especially in cooler regions where the more tropical C. rotundus does not grow. Cyperus esculentus is able to tolerate lower air temperatures (as low as -18°C). The two species apparently differ also in their thermal optima for growth.

Common Name: nutgrass

Duration: Perennial

Nativity: Non-Native

Lifeform: Graminoid

General: Perennial with wiry indurate stolons, springy when dried, 5-12 cm long, 1-2 mm in diameter, bearing tubers 3-8 mm in diameter, stems 10-35 cm tall, 0.5-3.5 mm in diameter, three sided, smooth, hardened basally.

Vegetative: Leaves 8-10, 5-30 cm long, 2-6 mm wide, v-shaped to flanged v-shaped, margins rough on the upper half.

Inflorescence: Subtending bracts 3-5, 0.5-10 cm long, 0.5-4 mm wide, v-shaped to flanged v-shaped, margins and keel rough, borne horizontal to ascendent to 45 degrees; rays 4-6, up to 10 cm, spikes 1, 15-25 mm long, 20-30 mm wide, broadly ellipsoid, spikelets 3-7, 4-40 mm long, 1.3-1.8 mm wide, linear, compressed, persistent rachilla, less than 0.5 mm wide, straight, with successive scales 1.5-2 mm apart, often red-speckled; 6-36 persistent scales, 2.5-3.5 mm long, 2-3 m wide, ovate, purple to reddish brown; achenes about 1.5 mm long, about 1 mm wide, three sided, ellipsoid, apex obtuse, base sessile, black.

Ecology: Found in a variety of habitats, often in disturbed sites.

Notes: Distinguished by the open spikes of linear reddish spikelets borne on a conspicuous slender rachis. Only this species and C. esculentus produce tuberiferous stolons.

Ethnobotany: The tubers were cooked and eaten, or eaten raw.

Etymology: Cyperus is from the Greek word meaning sedge, while rotundus means rounded.

Synonyms: None

Editor: SBuckley, 2010

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.

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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