4. Cyperus diffusus Vahl, Enum. Pl. 2: 321. 1805.
多脉莎草 duo mai suo cao
Perennials. Rhizomes short, hardened. Culms 25-80 cm tall, slightly thick, triquetrous, smooth, several leaved at basal part. Leaves equaling or shorter than culm; sheath pale green and eventually reddish brown; leaf blade 0.3-2 cm wide, flat, margin scabrous. Involucral bracts 6-12, leaflike, longer than inflorescence, 0.6-1.6(-1.9) cm wide. Inflorescence a decompound anthela; rays many, mostly 12-16 cm, each with 2-8 raylets. Spikelets 1-5, sessile, sometimes more than 3 at apex of raylets or tertiary raylets, oblong to linear-oblong, 3-7(-14) × 1.5-2 mm, slightly turgid, 6-12(-22)-flowered; rachilla narrowly winged. Glumes reddish brown or rusty brown on both surfaces but middle abaxially green or grayish green, lax, broadly ovate to orbicular-ovate, ca. 2 mm, 7-11-veined, keel prominent, apex rounded and with recurved mucro. Stamens 3; anthers linear, apex with white setae. Style very short; stigmas 3. Nutlet dark brown, ellipsoid, ca. 3/4 as long as subtending glume, 3-sided. Fl. and fr. Jun-Sep.
Forests in valleys, grasslands on mountain slopes, wet places by rivers, along trails, paddy fields; 100-1700 m. Guangdong, Guangxi, Hainan, Taiwan, SE Xizang, S Yunnan [Bhutan, Cambodia, India, Indonesia, Laos, Malaysia, Myanmar, Nepal, Philippines, Sri Lanka, Thailand, Vietnam; NE Australia, Indian Ocean islands, Pacific islands].
This was referred to as Cyperus laxus Lamarck by D. A. Simpson and T. Koyama (Fl. Thailand 6(4): 366. 1998), but G. C. Tucker (Syst. Bot. Mongr. 43: 44. 1994) noted a distinction between neotropical and paleotropical material, with the latter being recognized as C. diffusus, which we accept here.