Description from Flora of China
Onychium angustifolium Ching, Acta Phytotax. Sin. 20: 233. 1982, not O. angustifolium (Kunth) Kunze (1848).
Rhizomes long creeping or occasionally shortly creeping; scales dark brown, subulate-lanceolate. Fronds slightly dimorphic, mostly relatively closely spaced. Stipe straw-colored above a ± black base, 4-11 cm × ca. 1 mm. Lamina of sterile fronds narrowly lanceolate, 5-7 cm, pinnate-pinnatifid. Lamina of fer-tile fronds larger than sterile lamina, lanceolate or narrowly lanceolate, 7-12 × 1-3 cm, apex pinnatifid and long acuminate, 2-pinnate, thinly papery when dry, green to grayish green, not farinose. Lateral pinnae 7-15 pairs, strongly ascending obliquely, basal pair largest, deltoid-lanceolate or oblong-lanceolate, 1.5-2 × 0.4-0.5 cm. Pinnules (segments) of sterile fronds oblong, ca. 2 × 1 mm, apex acute or with 2 or 3 sharp teeth, 1 tooth per veinlet. Ultimate pinnules (segments) of fertile fronds linear, 4-8 × ca. 0.7 mm, base narrowly cuneate and narrowly winged-decurrent on costae, apex acuminate. Sori 3-6 mm. False indusia oblong to linear, entire.
Onychium angustifrons has lamina less divided than most other Onychium species and is small in stature, mostly less than 20 cm tall. It resembles O. moupinense in habit. Further studies are needed to show whether it is indeed a distinct species or merely a reduced form of O. moupinense in an extreme habitat.
● Exposed rock crevices. C Sichuan.