1. Athyrium filix-femina (L.) Roth (lady fern) Pl. 4c,d,e; Map 14

Rhizomes prostrate, short-creeping. Rhizome scales concolorous, light brown or dark brown, lanceolate to ovate. Leaves monomorphic, 30–125 cm long. Petioles straw-colored or reddish-tinged, shorter than the leaf blade, with light brown or dark brown scales, the bases with 2 vascular bundles. Leaf blades lanceolate to elliptic in outline, 2–3 times pinnately compound. Rachises glabrous to glandular or sparsely scaly. Pinnae 1–25 cm long, lanceolate to linear, the tips attenuate. Pinnules often deeply pinnately lobed, the margins toothed. Veins not anastomosing. Sori narrowly oblong to nearly linear, frequently hooked at the end or U-shaped. Indusia attached laterally or on the inner side of the U-shaped sorus, arching over the sori. Spores 64 per sporangium, monolete, 27–65 mm long, yellow to dark brown. 2n=80. June–October.

Scattered nearly throughout Missouri (U.S., Canada, south to South America, Europe, Asia). Mesic forests in ravines and cherty sinkholes, bottomland forests, banks of streams and spring branches, mostly on acidic substrate types; also on ledges of shaded sandstone and granite bluffs.

As presently circumscribed, A. filix-femina consists of five subspecies, two of which occur in Missouri. Some botanists prefer to consider these as separate species, and there is some evidence that hybrids between the two taxa are sterile. No such hybrids have been documented from Missouri as yet. Unfortunately most of the morphological characters used to distinguish the two taxa show some degree of overlap, and their separation often requires a weighted judgment among the several characters. This complex obviously requires more detailed study, but it seems most prudent to recognize the two Missouri taxa as subspecies for the present.