Description from Flora of China
Rhizomes long creeping; scales brown or reddish brown, lanceolate. Fronds slightly dimorphic (fertile fronds slightly more coarsely divided than sterile ones), mostly widely spaced. Stipe 7-45(-60) cm, 2-4 mm in diam., straw-colored throughout or with a brown to dark brown base, dark color sometimes extending to rachis abaxially. Lamina ovate-deltoid or narrowly ovate, (9-)20-48 × 10-20 cm, apex acuminate, finely 2-pinnate-pinnatifid to 4-pinnate, firmly papery when dry, green to dark green or grayish green, not farinose. Lateral pinnae 10-15 pairs, deltoid-lanceolate or oblong-lanceolate; basal pair largest, 9-20 × 5-10 cm, stalked to 1-2 cm, apex acuminate. Ultimate fertile pinnules (segments) crowded, sometimes overlapping, linear to linear-lanceolate, 4-10 × 1-2 mm, apex acute. Ultimate sterile pinnules (segments) similar to fertile ones but mostly somewhat shorter, apex shortly acuminate. Sori (2-)3-6 mm. False indusia extending nearly to midvein, entire. 2n = 58, 87, 116, 174.
The Onychium japonicum/O. moupinense group is a polyploid complex whose taxonomy requires further study. Although the two varieties reported for China have been treated as separate species by some botanists, they exhibit a great deal of morphological overlap and perhaps should not be formally recognized.
Stream banks, roadsides, forest margins, mountain slopes; 200-2400 m. Anhui, Fujian, Gansu, Guangdong, Guangxi, Guizhou, W Hebei, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Shaanxi, Shandong, Sichuan, Taiwan, Xizang, Yunnan, Zhejiang [Bhutan, India, Indonesia, Japan, Korea, Myanmar, Nepal, Pakistan, Philippines, Thailand, Vietnam; Pacific islands].