Stem scales brown. Leaves 5--30 cm. Petiole reddish brown to black, 0.75--2 mm diam. Blade lanceolate to deltate, 3--5-pinnate proximally, leathery, abaxially covered by dense white farina, adaxially glabrous or sparsely glandular; rachis rounded to slightly flattened adaxially. Pinna costae straight to slightly flexuous, branches not arising from prominent angles. Ultimate segments not articulate, dark color of stalks continuing into segment bases abaxially; segment margins recurved, often concealing sporangia; veins obscure adaxially. Sporangia submarginal, borne on distal 1/2 of secondary veins, containing 32 spores. Populations of Argyrochosma limitanea represent two morphologically distinctive taxa treated here as subspecies. For the most part, these taxa have different geographic ranges, and genetic interaction between them is precluded because both are asexual triploids. Isozyme analyses indicate that the two subspecies have different polyploid origins, but evolutionary relationships (and proper taxonomic treatment) cannot be resolved until sexually reproducing (64-spored) progenitors are found.

General: Usually on rock, stem compact, erect to ascending, scales brown with a reddish brown to black petiole 0.75-2 mm in diameter. Leaves: Clustered, blade lanceolate to deltate with 3-5 pinnate proximally, leathery, 5-30 cm long; covered beneath with dense white farine, upper surface glabrous or sparsely glandular, rachis rounded to slightly flattened above; pinna costae straight to slightly flexuous, branches not arising from prominent angles; ultimate segment margins recurved, often concealing sporangia; veins obscure above. Sporangia: Submarginal, borne on lower half of secondary veins with 32 spores. Ecology: Found on calcareous or volcanic substrates, on rocky slopes and along cliffs from 2,500-8,000 ft (1676-2438 m); sporulating summer-fall. Notes: Two subspecies in our area: ssp. limitanea and ssp. mexicana. Distinguished by the blades broadly deltate-ovate, 4-5 pinnate, with with lower pinnate at least half as long as blades in ssp. limitanea. Ssp. mexicana has blades lanceolate to oblong, 3-4 pinnate, with lower pinnate only a quarter to one third as long as blades. Both are found in similar habitats, with ssp. mexicana ranging slightly higher in elevation from 5,500–8,000 ft (1676–2438 m) and has a global rarity rank of G4T4; while ssp. limitanea ranges throughout the elevations. Etymology: Argyrochosma comes from Greek argyros, silver and chosma, mound, a reference to the powdery substance on the leaves, while limitanea means that which is on the border. Sources: FNA 1993