31. Cyperus difformis Linnaeus, Cent. Pl. 2: 6. 1756; Boiss., Fl. Or. 5: 370. 1882; C.B.Clarke, l.c. 599; R.R.Stewart, l.c. 88; Holm & al., World's Worst Weeds fig. 93. 1977; D. Traoré in Candollea 36: fig.5. 1981; Kukkonen in Rech.f., l.c. 126.
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.
Fl. Per.: July – October.
Type: "Habitat in India.".
Rice fields, ditches, irrigation channels, grassy swamps; 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.