Stem scales brown. Leaves 5--25 cm. Petiole dark brown, 0.75--1.5 mm diam. Blade deltate, 4--6-pinnate proximally, leathery to somewhat herbaceous, abaxially covered by whitish farina, adaxially glabrous or glandular; rachis rounded adaxially. Pinna costae distinctly flexuous, branches arising from prominent angles. Ultimate segments not articulate, dark color of stalks continuing into segment bases abaxially; segment margins plane to recurved, often partially concealing sporangia; veins usually obscure adaxially. Sporangia submarginal, borne on distal 1/4 of secondary veins, containing 64 spores. 2 n = 54. Sporulating summer--fall. Rocky slopes and cliffs; usually on granitic or volcanic substrates; 1700--3000 m; Colo., N.Mex., Wyo.; Mexico in Sonora. Argyrochosma fendleri is occasionally confused with A . limitanea , which can have slightly flexuous rachises and pinna costae. All A . limitanea specimens with slightly flexuous rachises and costae have 32 spores per sporangium, whereas specimens of A . fendleri consistently have 64. This southern Rocky Mountain species is the only member of the genus that is found on acidic substrates such as granite.

General: Erect fern from stout rhizomes with narrowly lanceolate scales that are pale orange brown. Leaves: Densely tufted fronds 5-25 cm long, on stipe 3-16 cm long, terete to slightly adaxially flattened, four to five pinnate, pinnae alternate; laminae elliptical to asymetrically triangular, 5-15 cm long, 5-12 cm wide, 4-6 pinnate, obtuse at base, acute at apex, with ultimate segments ovate to elliptical or lanceolate, upper surface glabrous, dense white farina beneath; curled upward when dry. Sporangia: Submarginal, borne on outer quarter of secondary veins, partly covered by the recurved margins of the segments, lacking indusium. Ecology: Found in crevices among rocks, often on limestone in dry sites from 5,500-10,000 ft (1676-3048 m); sporulates in summer and fall. Notes: Occasionally confused with A. limitanea which has slightly flexible rachises and pinnae. Distinguishing features are the fact that A. limitanea always has 32 spores per sporangium, which this species always has 64. Ethnobotany: A poultice of the plant was applied to lips for cold sores. Etymology: Argyrochosma comes from Greek argyros, silver and chosma, mound, a reference to the powdery substance on the leaves, while fendleri is named for Augustus Fendler (1813-1883) a German plant collector who worked for Asa Gray. Sources: FNA 1993, Windham 1987, Dittmer et al 1954, Lellinger 1985