Description from Flora of China
Cyperus michelianus (Linnaeus) Link subsp. pygmaeus (Rottbøll) Ascherson & Graebner.
Annuals. Roots fibrous. Culms tufted, 12-18 cm tall, compressed triquetrous, slightly concave on 3 sides, few leaved basally. Leaves shorter than culm; sheath reddish brown, short; leaf blade 2-2.5 mm wide, flat, apical margin and midvein abaxially spinulose. Involucral bracts 4-7, leaflike, longer than inflorescence, ± horizontal to sometimes downward reflexed. Inflorescences capitate, with numerous spikelets. Spikelets densely aggregated, narrowly oblong-ovoid to suboblong, 4-5 × ca. 1.5 mm, 10-15-flowered. Glumes yellowish white but middle rusty brown and shortly striate, distichous, oblong-lanceolate, ca. 2 mm, 3-veined, midvein green and apically forming a slight keel, apex acute and excurved mucronate. Stamen usually 1; anther short, linear; connective slightly prominent beyond anthers. Style short; stigmas 2(or 3), longer than style. Nutlet oblong, 1-1.2 mm, 2/3-3/4 as long as subtending glume, lenticular with one flat and one convex side, minutely papillose. Fl. and fr. Oct-Nov. 2n = 76.
Pond margins, water margins, wet places in sand; ca. 100 m. Anhui, Guangdong, Guangxi, Hainan, Henan, Hubei, Taiwan, Zhejiang [Afghanistan, India, Indonesia, Japan, Kashmir, Korea, Laos, Myanmar, Pakistan, Papua New Guinea, Philippines, Sri Lanka, Thailand, Vietnam; Africa, SW Asia, Australia, S Europe, Indian Ocean islands, Madagascar].