Petiole 15--45(--60) cm, base densely scaly; scales brown or dark brown, lanceolate or ovate-lanceolate, (7--)10--20 × (1--)2--5 mm, ± crisped. Blade elliptic to oblanceolate, 1--2-pinnate-pinnatifid, 25--120 × 10--50 cm, gradually narrowed proximally, broadest at or just above middle, apex acuminate. Pinnae very short-stalked or sessile, linear-oblong or oblong, apex acuminate. Pinnules sessile, narrowly deltate or oblong-lanceolate, base basiscopically broadly cuneate, acroscopically truncate, ± auriculate, apex obtuse to ± acute. Rachis , costae, and costules glabrous or with scales or pale glands. Sori round to elliptic, hooked at distal end, or horseshoe-shaped, medial to supramedial; indusia long-ciliate with nonglandular marginal hairs as long as or longer than width of indusia. Spores yellow. 2 n = 80.

Moist woods, swamps, streambanks; 10--1600 m; Alta., B.C., Man., N.W.T., Ont., Que., Sask., Yukon; Alaska, Calif., Idaho, Mont., Oreg., S.Dak., Wash., Wyo.

Athyrium filix-femina var. cyclosorum is most similar to the European var. filix-femina ; it differs in having broader, nearly equilateral pinnules and medial to supramedial sori. The variety is distributed in northwestern North America with disjunct populations in northwestern Quebec and Ontario.