Athyrium alpestre var. americanum

Stems ascending or short-creeping. Petiole straw-colored or red-brown distally, (7--)10--30 cm, base dark red-brown to black with 2 rows of teeth, swollen; scales at base brown to dark brown, lanceolate or broadly lanceolate, 13 × 3(--5) mm. Blade narrowly elliptic or lanceolate, 2--3-pinnate-pinnatifid, 15--55(--65) × 3--25 cm, moderately narrowed proximally, broadest below middle, apex acuminate. Pinnae short-stalked, narrowly deltate to deltate-oblong, apex acute. Pinnules deeply pinnatifid, segments oblong, crenulate. Rachis , costae, and costules with small, pale brown scales. Veins pinnate. Sori round to elliptic; indusia absent or very minute, scalelike. 2 n = 80.

Wet talus slopes, rocky hillsides, alpine meadows; 600--3100 m; Greenland; Alta., B.C., Nfld., Que., Yukon; Alaska, Calif., Colo., Idaho, Mont., Nev., Oreg., Utah, Wash., Wyo.

Athyrium alpestre var. americanum differs from var. distentifolium of Europe in its more finely dissected leaves with crenulate pinnule-segments, relatively broader pinnae with abruptly larger basal pinnules, and much more rudimentary indusia, if any. Japanese plants are more similar to var. americanum than to var. distentifolium , and they need further study.