Plants on rock. Stems decumbent to erect, or creeping, few to many branched; scales colorless or brownish, concolored or bicolored, ovate, lanceolate or linear, margins entire. Leaves dimorphic, scattered or densely tufted; fertile leaves 5--25 cm; sterile leaves 3--20 cm, shorter than fertile leaves. Petiole dark brown proximally, light brown to green distally, with single longitudinal groove adaxially, scaly, with single vascular bundle. Blade deltate, lanceolate to elliptic, 2--4-pinnate, somewhat leathery or herbaceous to membranaceous, abaxially glabrous, adaxially glabrous or sparsely pubescent, dull to somewhat lustrous, not striate; rachis straight. Ultimate segments of blade short-stalked or sessile, free or adnate to midrib; stalks dull, green; segments of sterile leaves ovate, elliptic, obovate, or fan-shaped, usually less than 4 mm wide, margins plane, dentate or shallowly to deeply cut; fertile segments strongly differentiated from sterile segments, lanceolate to linear, usually less than 2 mm wide, margins reflexed to form false indusia extending over entire length of segments, at first covering young sporangia, often becoming plane at maturity. Veins of ultimate segments usually obscure, free, pinnately branched and divergent distally. False indusia greenish to brown, broad, clearly marginal, usually concealing sporangia. Sporangia scattered along veins on abaxial leaf surface, often intermixed with farina-producing glands, containing 64 spores. Spores yellow, tetrahedral, trilete, verrucose, equatorial flange absent. Gametophytes glabrous. x = 30.
Lvs small, evergreen or deciduous, dimorphic; petiole weak, glabrous or merely hairy, scaly only at the base, stramineous to greenish at least distally; blades glabrous, bipinnate to tripinnate, the sterile ones spreading, membranous, with largely green rachis, the ultimate segments dentate or crenate, the veins not reaching the margin; fertile lvs more erect and surpassing the sterile ones, with narrow, entire ultimate segments, the revolute margin modified into a false indusium covering the sori, which are borne on the vein-tips. 2-4, N. Hemisphere.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.