笔草 bi cao

Pogonatherum contortum Brongniart in Duperrey, Voy. Monde 2(2): 90. 1831; Erianthus contortus (Brongniart) Kuntze.

Culms erect, 25–50 cm tall. Leaf sheaths glabrous; leaf blades becoming involute, 10–30 × 0.1–0.2 cm, abaxial surface glabrous, adaxial surface thinly pilose; ligule ca. 0.2 mm. Racemes 1–20, subdigitate, 3–6 cm, white hairy, tough, all spikelets pedicelled, disarticulating from pedicels at maturity; pedicels usually unequal, as long as or shorter than internode, villous. Spikelets 1.8–3 mm, brown, glossy; callus hairs up to 1/2 spikelet length; lower glume narrowly oblong or lanceolate-oblong, pubescent to villous except near apex, or sometimes glabrous, upper flanks pilose, apex 2-toothed; upper glume with mucro or awn 0.5–4(–12) mm; lower lemma ca. 1 mm; upper lemma entire or minutely toothed; awn 1.5–3 cm, column pilose, hairs ca. 1 mm. Anthers 1–3, ca. 0.5 mm.

Grassy places on mountain slopes, open and disturbed grassy hillsides, sometimes gregarious; 700–1700 m. Fujian, Guangdong, Guangxi, Hainan, Jiangxi, Sichuan, Yunnan [Bhutan, India, Indonesia, Myanmar, Nepal, Thailand, Vietnam; Australia, Pacific Islands].

This widespread, annual species comprises a variable complex of many intergrading forms, some of which have been accorded separate status, either at specific or infraspecific rank. Two varieties have been recognized in China; var. contortum, with callus hairs less than 1/2 the spikelet length and pedicels of the spikelet pairs unequal, occurs in Indonesia and Australia.