Low herb forming loose mats. Culms slender, creeping, rooting and branching at nodes, flowering branches up to 15 cm tall. Leaf sheaths thinly pubescent, outer margin ciliate; leaf blades lanceolate-ovate, thin, 2–3.5 × 0.5–0.9 cm, abaxial surface glabrous or pilose, adaxial surface hispid with long scattered hairs, margins white, finely scabrid, base obtuse, apex shortly acuminate; ligule ca. 1 mm. Panicle broadly ovate in outline, 2–8 cm, eglandular, rather sparsely branched, spikelets 10–50; branches and pedicels widely spreading, very slender, scaberulous. Spikelets broadly elliptic, (1.3–)1.5–1.8 mm, green infrequently tinged purplish; florets similar; glumes equal to spikelet or lower slightly shorter, ovate-elliptic, shortly hispid above the middle, often with a few stout, sometimes overtopping bristles, apex obtuse, lower glume 3–5-veined, upper glume 5–7-veined; lemmas broadly elliptic, leathery, thinly pubescent near margins and apex. Fl. and fr. summer to autumn. 2n = 40.

Isachne nipponensis is very close to I. myosotis, but has a rather looser growth, larger leaves and spikelets, and a broader, very open panicle with slender, scaberulous branches.

Isachne nipponensis var. kiangsiensis P. C. Keng (Acta Phytotax. Sin. 10: 21. 1965), described from Jiangxi, has smooth, glandular panicle branches and pedicels and may represent a different species.

Wet shady places; below 1000 m. Fujian, Guangdong, Guangxi, Guizhou, Hunan, Jiangxi, Sichuan, Taiwan, Zhejiang [Japan, Korea (Cheju Island)].