Description from Flora of China
Onychium japonicum (Thunberg) Kunze var. parvisorum Bonaparte.
Rhizomes stout, decumbent; scales dark brown, shiny, subulate-lanceolate. Fronds monomorphic or nearly so (fully fertile fronds slightly more coarsely divided than entirely sterile ones, but many fronds intermediate), closely spaced, often appearing clustered. Stipe straw-colored above a brown base, (12-)25-30 cm × ca. 4 mm. Lamina deltoid-oblong or deltoid-ovate, 35-60 × 20-30 cm, apex acuminate, 4- or 5-pinnate-pinnatifid, thinly herbaceous when dry, bright green to grayish green, not farinose. Lateral pinnae 9-15 pairs, basal pair largest, (8-)15-22 × 6-16 cm, stalked to ca. 1.5 cm, apex acuminate. Pinnules deltoid or elongate ovate, stalked; stalks with narrow wings. Ultimate segments crowded, sometimes overlapping, linear to narrowly oblanceolate, 2-3(-7) × ca. 1 mm, apex acuminate. Sori 1-3 mm. False indusia extending nearly to midvein, margins entire. 2n = 116.
Forests and ditches; 1200-2800 m. SW Sichuan, NW Yunnan [Bhutan, India, Nepal, Thailand].