Culms creeping, smooth and glabrous, 15–60 cm tall. Leaf sheaths loosely pilose with tubercle-based hairs; leaf blades lanceolate, 3–15 × 0.3–2 cm, pubescent on both surfaces or subglabrous, basal margins with a few long, stiff, tubercle-based hairs, apex acuminate; ligule 0.5–2 mm, subrounded. Panicle 5–30(–40) cm, often diffuse, branches loosely ascending to widely spreading, very slender, glabrous; pedicels filiform, longer than spikelets. Spikelets purplish at maturity, 1.3–1.8 mm, varying from glabrous to appressed-pubescent or shortly hispid with stiff, conspicuously tubercle-based hairs; glumes 3-veined, the lower ca. 1/2 spikelet length, the upper 2/3 spikelet length; lower lemma subequaling spikelet, margins ciliate, apex obtuse; upper lemma minutely pitted. Anthers ca. 0.8 mm. Fl. and fr. Sep–Feb. 2n = 18, 36.

Cyrtococcum patens is a very variable species, and specimens with large, diffuse panicles have a different habit from small- or narrow-panicled forms. This difference is acknowledged here at varietal rank, but it should be realized that variation is continuous and intermediates will be encountered.

Spikelet pubescence varies from completely glabrous, through forms with sparse to dense, short, appressed hairs, to forms with some or all of the basal hair tubercles enlarged and prominent. This last-mentioned form has been separated as var. schmidtii (Hackel) A. Camus. It is found throughout the entire size range of the species, and also over the whole geographic range, and is not taxonomically significant.

Moist places in grasslands and forests. Fujian, Guangdong, Guangxi, Guizhou, Hainan, Hunan, Jiangxi, Sichuan, Taiwan, Xizang, Yunnan [Bangladesh, Bhutan, India, Indonesia, Japan (Ryukyu Islands), Malaysia, Myanmar, Nepal, Philippines, Sri Lanka, Thailand, Vietnam; Pacific Islands (Polynesia)].