7. Sporobolus diandrus (Retzius) P. Beauvois, Ess. Agrostogr. 26. 1812.
双蕊鼠尾粟 shuang rui shu wei su
Agrostis diandra Retzius, Observ. Bot. 5: 19. 1788 ["1789"]; A. elongata var. flaccida Roth ex Roemer & Schultes; Sporobolus indicus var. flaccidus (Roth ex Roemer & Schultes) Veldkamp; Vilfa diandra (Retzius) Trinius; V. retzii Steudel, nom. illeg. superfl.
Perennial. Culms tufted, erect, 30–90 cm tall. Leaf sheaths glabrous but margin ciliate; leaf blades linear, usually involute, 5–30 × 0.2–0.3 cm, glabrous on both surfaces or adaxial surface distinctly pilose at base, tapering to a long filiform apex; ligule 0.2–0.3 mm. Panicle contracted or rather loose, 7–35 × 1.5–3.5 cm; branches 1.5–9 cm, ascending or obliquely spreading, loosely spiculate, often lower 1/3 bare. Spikelets silvery grayish or yellowish green, 1.4–1.7 mm; lower glume oblong, ca. 0.5 mm, veinless, truncate or obtuse; upper glume oblong-ovate, 1/2–2/3 spikelet length, obscurely 1-veined, acute or obtuse-erose; lemma ovate-oblong, as long as spikelet, indistinctly 1 (–3)-veined, acute to obtuse. Anthers 2(–3), 0.5–0.8 mm. Grain obovate to oblong, 0.6–0.9 mm, apex truncate. Fl. and fr. May–Aug. 2n = 24.
Dry hill slopes, grassy fields, roadsides, beaches. Fujian, Guangdong, Guangxi, Guizhou, Sichuan, Taiwan, Yunnan [Bhutan, India, Indonesia, Japan (Ryukyu Islands), Malaysia, Myanmar, Nepal, Pakistan, Philippines, Sri Lanka, Thailand; Australia].
Sporobolus diandrus and S. fertilis are elements of the polymorphic, pantropical species complex of S. indicus (Linnaeus) R. Brown. This complex includes a range of intergrading taxa encompassing chromosome numbers from 2n = 18 to 2n = 54. Due to the small differences between these taxa and the frequency of intermediates, they are sometimes regarded as varieties of a broadly defined S. indicus.