2. Athyrium filix-femina (Linnaeus) Roth ex Mertens, Arch. Bot. (Leipzig). 2(1): 106. 1799.
Lady fern, athyrie fougère-femelle
Polypodium filix-femina Linnaeus, Sp. Pl. 2: 1090. 1753
Stems short-creeping or ascending. Petiole straw-colored distally, 7--60 cm, base dark red-brown or black, swollen, with 2 rows of teeth; scales light to dark brown, linear- to ovate-lanceolate, 7--20 × 1--5 mm. Blade elliptic, lanceolate to oblanceolate, 2-pinnate to 2-pinnate-pinnatifid, 18--30 × 5--50 cm, herbaceous but with cartilaginous margin, narrowed to base, apex acuminate. Pinnae sessile to short-stalked, linear-oblong to lanceolate, apex acuminate. Pinnules pinnatifid, segments oblong-linear to narrowly deltate, margins serrate. Rachis , costae, and costules glabrous or with glands or hairs. Veins pinnate. Sori straight, hooked at distal end, or horseshoe-shaped; indusia dentate or ciliate.
Varieties ca. 5 (4 in the flora): North America, Mexico, Central America, South America, Europe, Asia.
Athyrium filix-femina is circumboreal, and this or closely related species extend into Mexico, Central America, and South America. The delimitation and infraspecific classification of A . filix-femina need detailed study.