Description from Flora of China
Plants terrestrial or less commonly on rocks. Rhizomes long creeping or rarely short and decumbent, siphonostelic, scaly, scales concolorous, light brown to reddish brown, opaque to somewhat translucent, non-clathrate, linear-lanceolate to ovate-lanceolate, margins entire. Fronds monomorphic to somewhat dimorphic, widely or closely spaced. Stipe straw-colored above a usually darker proximal portion, occasionally uniformly straw-colored or reddish brown to dark brown (especially abaxially), glabrous above scaly base, with (1 or)2 vascular bundles at base, adaxially grooved. Lamina ovate-deltoid or ovate-lanceolate, less often elongate lanceolate, herbaceous or papery, finely 2-5-pinnate-pinnatifid, rarely 2-pinnate, glabrous or nearly so or fertile segments yellow-farinose abaxially; rachis and costae usually grooved adaxially. Pinnae alternate. Ultimate segments or lobes narrow and small, lanceolate to oblong-lanceolate or narrowly oblong, base cuneate and often decurrent, apex acute or acuminate. Veins simple or pinnately branched, free, slightly thickened, sometimes raised abaxially, in fertile segments veinlets connected by an inframarginal commisural vein. Sori borne along commisural veins, linear. False indusia usually well developed, membranous, continuous but interrupted at segment apex and base, reaching to midvein or nearly so (narrow in Onychium tenuifrons), margins entire, slightly undulate, or less commonly erose. Spores trilete, globose-tetrahedral, perispore coarsely tuberculate-reticulate on distal face, proximal face tuberculate and with prominent, coarse ridges parallel to equatorial flange. x = 29.
The taxonomy of Onychium is poorly understood and is complicated by polyploidy and apomixis in several of the taxa. The descriptions below contrast sterile and fertile fronds, but it should be noted that plants of some species often also produce intermediate fronds that are fertile distally and sterile proximally. Small specimens of Onychium sometimes are confused with dissected-leaved Asplenium species; collectors should examine rhizome scales (clathrate in Asplenium), sori (true indusia lateral on veins in Asplenium), and spores (monolete, mostly ellipsoid, and lacking an equatorial flange in Asplenium).
About ten species: tropical and subtropical Africa (one species), Asia; eight species (two endemic) in China.
(Authors: Zhang Gangmin (张钢民); George Yatskievych)