4. Microstegium japonicum (Miquel) Koidzumi, Bot. Mag. (Tokyo). 43: 394. 1929.
日本莠竹 ri ben you zhu
Pollinia japonica Miquel, Ann. Mus. Bot. Lugduno-Batavi 2: 290. 1866; Leptatherum japonicum (Miquel) Franchet & Savatier; Microstegium nudum (Trinius) A. Camus subsp. japonicum (Miquel) Tzvelev.
Annual. Culms trailing, rooting at lower nodes, up to 80 cm long, nodes glabrous. Leaf sheaths glabrous, one margin ciliate; leaf blades ovate-lanceolate, 2–5 × 0.6–1.2 cm, glabrous, midvein obscure except near base, base rounded, apex acute; ligule 0.2–0.5 mm. Racemes 3–7, very slender, slightly flexuous, lower becoming divaricate, 4–6 cm; rachis internodes filiform, glabrous, longer than spikelet; spikelets both pedicelled, shorter pedicel ca. 1 mm, longer 2.5–3 mm. Spikelets 3–4 mm; callus very shortly bearded or subglabrous in lower spikelet; lower glume narrowly lanceolate-oblong, back shallowly concave, 2–4-veined, keels scabrid, otherwise smooth, apex attenuate, hyaline, subacute or minutely 2-toothed; upper glume weakly keeled or rounded on back, apex acuminate; lower lemma lanceolate, hyaline, slightly shorter than glumes; upper lemma linear, hyaline, emarginate; awn very fine, flexuous, ca. 1 cm, apex hairlike, tangled; upper palea absent or minute. Anthers 2, 0.5–0.7 mm. Fl. and fr. Jul–Sep.
Mountainsides, forest margins, roadsides. Anhui, Hubei, Hunan, Jiangsu, Jiangxi, Zhejiang [Japan, Korea].
This species is very close to Microstegium nudum, but differs mainly in its pedicelled spikelets.