石茅 shi mao

Holcus halepensis Linnaeus, Sp. Pl. 2: 1047. 1753; Andro-pogon halepensis (Linnaeus) Brotero; A. sorghum (Linnaeus) Brotero subsp. halepensis (Linnaeus) Hackel.

Perennial with vigorous spreading rhizomes. Culms 0.5–1.5 m tall, 4–6 mm in diam.; nodes puberulous. Leaf sheaths glabrous; leaf blades linear or linear-lanceolate, 25–80 × 1–4 cm, glabrous; ligule 0.5–1 mm, glabrous. Panicle lanceolate to pyramidal in outline, 20–40 cm, soft white hairs in basal axil; primary branches solitary or whorled, spreading, lower part bare, upper part branched, the secondary branches tipped by racemes; racemes fragile, composed of 2–5 spikelet pairs. Sessile spikelet elliptic, 4–5 mm; callus obtuse, bearded; lower glume subleathery, often pale yellow or yellowish brown at maturity, shortly pubescent or glabrescent, 5–7-veined, veins distinct in upper part, apex 3-denticulate; upper lemma acute and mucronate or 2-lobed and awned; awn 1–1.6 cm. Pedicelled spikelet staminate, narrowly lanceolate, 4.5–7 mm, often violet-purple. Fl. and fr. summer–autumn. 2n = 40.

Introduced. Streams, valleys, waste ground, a weed in fields. Anhui, Fujian, Guangdong, Hainan, Sichuan, Taiwan, Yunnan [India, Kazakhstan, Kyrgystan, Nepal, Pakistan, Sri Lanka, Tajikistan, Turkmenistan, Uzbekistan; SW Asia, S Europe].

This species is thought to have originated in the Mediterranean region, but is now widely distributed as a serious weed in warm-temperate regions of the world. The forage known as Johnson Grass is a selection of Sorghum halepense. It introgresses with grain sorghum (S. bicolor) where both species grow together.