Description from Flora of China
Cyperus rotundus Linnaeus subsp. tuberosus (Rottbøll) Kükenthal.
Perennials. Rhizomes stoloniferous; stolons long and creeping, terminated by a tuber. Culms solitary, rarely few laxly tufted, 20-55 cm tall, slender, triquetrous, smooth, basally with several leaves. Leaves shorter than culm; sheath reddish brown, eventually disintegrating into fibers; leaf blade medium green, 3-6 mm wide, base flat or slightly folded. Involucral bracts 2 or 3, leaflike, shorter than or equaling inflorescence. Inflorescence a simple or rarely compound anthela; rays 2-6, to 8 cm, unequal in length. Spikes obdeltoid, with 2-11 laxly arranged spikelets. Spikelets linear, 0.8-2 cm × 1.5-2 mm, obliquely spreading, 8-20-flowered; rachilla wings white, broad, hyaline. Glumes brownish yellow to straw-colored on both surfaces but keel green, broadly ovate to elliptic, 3.5-4 mm, membranous, conspicuously 7-veined (nearly reaching margin), margin white hyaline, apex rounded. Stamens 3; anthers linear; connective slightly prominent beyond anthers. Style of medium length; stigmas 3. Nutlet oblong-obovoid, ca. 1/2 as long as subtending glume, 3-sided, puncticulate. Fl. and fr. Jun-Jul.
Open grasslands, along trails, sandy shores, gardens; below 1700 m. Sichuan, Taiwan, Yunnan [India, Japan (Ryukyu Islands), Malaysia, Sri Lanka; Africa, SW Asia (Yemen), Indian Ocean islands].