Cyperus difformis L.

Cyperus difformis is naturalized in the New World and native to the Old World, where it ranges from southern Europe to southern Africa and eastward to Southeast Asia and Australia.

Herbs, annual, cespitose. Culms 1–15, trigonous, 7–30 cm × 1.2–2.5 mm, soft (flattened in pressing), glabrous. Leaves 2–7, flat, (2–)7–22 cm × 2.2–4 mm. Inflorescences: heads dense, 7–17 mm diam.; when rays short, heads sessile or nearly so, then densely irregularly lobate, 12–35 mm diam.; rays 1–5, 2–32 mm; bracts 2–4, longest bract erect or nearly so, appearing as continuation of culm, other bracts horizontal to ascending, 1–22 cm × 0.5–3.5 mm, margins and keel minutely scabridulous. Spikelets 30–120, greenish brown to purplish brown, oblong-ellipsoid, compressed, (2–)3–5(–6) × 0.8–1.2 mm; floral scales (6–)12–20(–30), laterally clear margins, stramineous to deep purple, medially greenish, stramineous, or purplish, laterally ribless, medially 3-ribbed, obovate to orbiculate, 0.6–0.8 × 0.6–0.8 mm, apex mucronulate. Flowers: stamens 1 or 2; anthers ovoid-ellipsoid, 0.1 mm, connective not prolonged; styles 0.1 mm; stigmas 0.1–0.3 mm. Achenes light brown, obovoid-ellipsoid, 0.6–0.8 × 0.3–0.4 mm (as long as subtending scale), base cuneate, apex obtuse, apiculate, surfaces finely reticulate, papillose.

Annual, 25-60 cm. Roots reddish-brown. Stem c. 3 mm diam., sharply trigonous, smooth. Leaves shorter than stem; sheaths to c. 10 cm, green or yellow-brown, sometimes with reddish tint, mouth oblique; ligule c. 1 mm, papery, arch of attachment higher than wide; blades up to 50 cm, 3-5 mm wide, keeled, margins smooth, apex trigonous, scabrous. Inflorescence of 1-7 globose partial inflorescences, nearly sessile or peduncles to 30 mm; partial inflorescences 7-15 mm diam., axis tightly digitately branching and rebranching, with c. 100 or more sessile spikes. Bracts 2-3, lowest two foliose, to 20 cm or more, sheath-less. Spikes 2-5 x c. 1 mm, with 5-20 flowers; glumes c. 0.7 mm, deeply cymbiform, blunt, wider than long, midnerve strong, sides brown or dark brown, margins narrowly scarious; rachis compressed, slightly zigzagging, internodes c. 0.8 mm. Stamens 2. Nut c. 0.5 mm, obovoid, sharply trigonous, papillose, yellowish.

Tropical, subtropical and temperate regions of both hemispheres. Common in rice fields.

introduced; Ala., Ariz., Calif., Fla., Ga., Idaho, Ky., La., Miss., N.J., N.Mex., N.C., Oreg., Pa., S.C., Tenn., Tex., Va.; Mexico; West Indies (Puerto Rico); Central America (Nicaragua, Panama); South America; Eurasia; Indian Ocean Islands; Pacific Islands; Australia.

Distribution: Common weed from 35o S to 45o N in tropical and subtropical areas of all continents; from S. Europe to Turkey, Iraq, Caucasus, Uzbekistan, Tadjikistan, Pakistan and India.

100-2700 m

Fl. Per.: July – October.

Fruiting summer.

Disturbed, muddy soils, shallow waters; 0–1000m.

Rice fields, ditches, irrigation channels, grassy swamps.

Cyperus lateriflorus Torrey