10. Ischaemum rugosum Salisbury, Icon. Stirp. Rar. 1, t. 1. 1791.
田间鸭嘴草 tian jian ya zui cao
Andropogon rugosus (Salisbury) Steudel; A. segetum (Trinius) Steudel; Ischaemum akoense Honda; I. rugosum var. segetum (Trinius) Hackel; I. segetum Trinius.
Annual. Culms loosely tufted, erect to decumbent, 20–100 cm tall, often branching, nodes pubescent. Leaf sheaths loose, papery, lightly keeled, glabrous or pilose with scattered tubercle-based hairs, margins ciliate; leaf blades linear-lanceolate, 10–30 × 0.5–2 cm, glabrous or thinly pilose, margins scabrid, base variable, rounded and constricted, or attenuate and sometimes briefly pseudopetiolate, apex acuminate; ligule 2–5 mm. Racemes terminal and axillary, paired, appressed back to back or slightly separated, 3–11(–13) cm; rachis internodes inflated, thickly clavate, ciliate along midline, inner angles glabrous. Sessile spikelet oblong-ovate, 4–6 × ca. 2 mm; lower glume 2-keeled throughout, crustaceous, yellowish and transversely 4–7-ridged below, ridges sharp, mostly continuous, herbaceous above with many anastomosing green veins, keels scabrid, wingless or winged on one side, apex obliquely obtuse; awn of upper lemma 1.2–2 cm. Pedicelled spikelet dorsally compressed, variable in size, often much reduced especially toward raceme apex, awnless; pedicel elongate when spikelet rudimentary.
Marshy fields, ditch banks, river banks, other wet often slightly saline grassy places; 100–1800 m. Guangdong, Guangxi, Guizhou, Hainan, Sichuan, Taiwan, Yunnan [Bhutan, India, Indonesia, Malaysia, Myanmar, Nepal, Philippines, Sri Lanka, Thailand; Australia (Queensland); introduced in Africa and America].
This native of tropical Asia is now widespread as a weed in tropical parts of the world, especially as a weed of rice fields.