Plants terrestrial or on rock. Stems short- to long-creeping, stolons absent. Leaves monomorphic, dying back in winter. Petiole 1/3--3 times length of blades, base often swollen and persisting as trophopod over winter; vascular bundles 2, lateral, round or oblong in cross section. Blade ovate-lanceolate to deltate, 1--3-pinnate-pinnatifid, gradually reduced distally to a pinnatifid apex, membranaceous to herbaceous. Pinnae not articulate to rachis, segment margins crenulate, dentate, or serrate; proximal pinnae not reduced or 1 pair slightly reduced, sessile or petiolulate, equilateral or ± inequilateral, if inequilateral basiscopic side more narrowly cuneate; costae adaxially grooved, grooves continuous from rachis to costae; indument absent or of uniseriate, multicellular hairs in pinnae axils or of unicellular, gland-tipped hairs abaxially, absent adaxially. Veins free, simple or forked. Sori in 1 row between midrib and margin on ultimate segments, round; indusia ovate to lanceolate, hoodlike and arching over sorus toward margin, attached to receptacle base on costal side, persistent to ephemeral or often obscure at maturity. Spores brownish, echinate, or verrucate. x = 42. Cystopteris is a taxonomically difficult genus at the species level. Especially troublesome is the worldwide and polymorphic species C . fragilis sensu lato. To maintain it as a single species with several varieties would be easiest (and least controversial). This approach, however, may not accurately reflect true evolutionary history.