Description from Flora of China
Cyperus densespicatus Hayata; C. imbricatus var. densespicatus (Hayata) Ohwi; C. imbricatus subsp. elongatus (Boeckeler) T. Koyama; C. imbricatus var. elongatus (Boeckeler) Kükenthal; C. mediorubescens Hayata; C. radiatus Vahl; C. radiatus var. elongatus Boeckeler.
Perennials. Rhizomes short. Roots many, fibrous. Culms 7-15 cm tall, stout, obtusely 3-angled, smooth, basally clothed by several leaf sheaths. Leaves basal, shorter than culm; sheath reddish brown to dark brown, long; leaf blade 0.5-1.5 cm wide, basally folded, apically flat. Involucral bracts 3-5, leaflike, longer than inflorescence. Inflorescence a compound anthela; rays 6-10, to 16 cm, unequal in length, each with 3-10 raylets; raylets radially spreading. Spikes 3-6 fasciculate at apex of raylet, sessile or subsessile, densely arranged, cylindric, 1.5-4 × 0.6-1.4 cm, with many spikelets. Spikelets in several rows, narrowly ovoid to narrowly oblong-ovoid, 4-12 × 1.5-2 mm, slightly compressed, obliquely spreading, 8-30-flowered; rachilla wings white, narrow, hyaline, persistent; successive glumes 0.4-0.5 mm apart. Glumes brownish yellow to straw-colored, densely imbricate, broadly ovate, 1-1.2 mm (excluding mucro), shiny, 3-5-veined, keel greenish ending in a straight to slightly excurved 0.3-0.5 mm mucro. Stamens 3; anthers oblong, 0.2-0.5 mm; connective prominent beyond anther apex. Style long; stigmas 3. Nutlet obovoid to subellipsoid, ca. 1/2 as long as subtending glume, 3-sided, smooth. Fl. and fr. Sep-Oct.
Shallow water of ponds, shady moist places; 100-1400 m. Guangdong, Guangxi, Hainan, Taiwan [Afghanistan, Bangladesh, India, Japan, Laos, Malaysia, Myanmar, Nepal, Papua New Guinea, Philippines, Thailand, Vietnam; tropical Africa and America, SW Asia, Indian Ocean islands, Madagascar].