Polypodium fragile Linnaeus, Sp. Pl. 2: 1091. 1753; Aspidium fragile (Linnaeus) Swartz; Athyrium fragile (Linnaeus) Sprengel; Cyclopteris fragilis (Linnaeus) Gray; Cyste fragilis (Linnaeus) Dulac; Cystea fragilis (Linnaeus) J. Smith; Cystopteris filix-fragilis Gilibert.

Rhizomes shortly or long creeping, scaly at apex and stipe bases; scales brownish, broadly lanceolate. Fronds approximate or caespitose; fertile fronds (3.5-)20-35(-49) cm; stipe brown at base, upper part stramineous or chestnut-colored, usually shorter than lamina, nearly 1/3-2/3 as long as lamina, occasionally slender and slightly longer than lamina when plant in crevices, 5-14(-20) cm, (0.2-)1-1.5 mm in diam., with sparse, shiny scales; lamina usually 2-pinnate to 2-pinnate-pinnatifid, occasionally pinnate or 3-pinnate, lanceolate to broadly lanceolate, 17-28 × (0.8-)4-5(-8) cm, shortly acuminate at apex; pinnae 12-15 pairs, ascending, basal 1 or 2 pairs slightly shortened, or nearly not shortened, ovate to ovate-lanceolate, (0.4-)2-4(-7) × (0.2-)1-2.5 cm, obtuse or shortly acuminate, toothed at apex, subopposite, subsessile, widely separated from each other, usually 1-2 × as long as wide, 1.5-4.5 cm apart, base parallel to rachis on acroscopic side, ± cuneate on basiscopic side; pinnules 5-7 pairs, ovate or oblong, acroscopic side truncate, basiscopic side cuneate at base, sessile or shortly stalked, entire or toothed at margin, or pinnatifid, rounded or obtuse and toothed at apex; middle pinnae similar to lower pinnae, but slightly longer, separated from each other by 1.2-2.5 cm, subopposite or alternate, subsessile; upper pinnae pinnatipartite, toothed only on apices and acroscopic margin; veins pinnate, costules slightly tortuous, terminating in entire teeth. Lamina herbaceous when dried, green or yellow-green. Rachis and costae, especially their bases, ± with sparse unicellular to long multicellular hairs, even with few scale hairs. Sori small, orbicular, medial on veins, 2-4 pairs per pinnule, 1 or 2 sori at acroscopic side in upper pinnules; indusia pale green or brownish, ovate to lanceolate, membranous. Spores dark brown, perispore surface with regular, denser spines. 2n = 84*, 168, 252, 336.

According to Knapp (Ferns Fern Allies Taiwan, 445. 2011), Windham described several cytotypes for Taiwan (diploid, tetraploid, and hexaploid) in 2007; thus, further study of the taxon is pending. Many infraspecific taxa have been described from Europe.

Under alpine shrubs, in rock crevices on shaded slopes, base of rocks, damp areas at streamsides; (200-)1500-4500(-4800) m. Anhui, Gansu, Hebei, Heilongjiang, Henan, Jilin, Liaoning, Nei Mongol, Ningxia, Qinghai, Shaanxi, Shandong, Shanxi, W Sichuan, Taiwan, Xinjiang, Xizang, Yunnan [Afghanistan, India, Japan, Kashmir, Korea, Mongolia, Nepal, Pakistan, Russia; Africa, SW Asia (Iran, Turkey), Europe, North and South America].