Description from Flora of China
Poa japonica Thunberg in Murray, Syst. Veg., ed. 14, 114. 1784.
Annual. Culms erect, or geniculate at base, 30–100 cm tall, 1.5–2.5 mm in diam., 3–4-noded. Leaf sheaths usually loose, longer than internodes, glabrous; ligules scarious, ca. 0.5 mm, fimbriate at apex, pubescent on back; leaf blades flat, 3–25 × 0.3–0.5 cm, smooth and glabrous. Panicle elongated, 6–34 × 1.5–6 cm; branches slender, clustered or verticillate, glabrous in axils. Spikelets usually purplish at maturity, ovate, 1–2 mm, 4–8-flowered; rachilla distarticulating between florets from top downward at maturity. Glumes chartaceous, ovate-lanceolate, subequal, 0.6–0.8 mm, 1-veined, apex obtuse. Lemmas chartaceous, broadly elliptical, distinctly 3-veined, apex obtuse, lower lemma ca. 1 mm. Palea subequal to lemma, along 2 keels ciliolate. Stamens 2; anthers ca. 0.2 mm. Caryopsis red-brown, ovoid, 0.4–0.5 mm. Fl. and fr. Jun–Nov.
Fields, roadsides, stream banks. Anhui, Fujian, Guangdong, Guangxi, Guizhou, Henan, Hubei, Jiangsu, Jiangxi, Taiwan, Yunnan, Zhejiang [Bhutan, India, Indonesia, Japan, Malaysia, Myanmar, Nepal, New Guinea, Philippines, Thailand, Vietnam].