Thallus: areolate, sometimes irregular, rarely more than 2-3 cm wide areoles: irregular, 0.4-1.5 mm in diam., up to 0.9 mm thick, usually contiguous; rim: ±down-turned upper surface: reddish brown, dark, dull, plane to convex, smooth or fissured to deeply dissected, epruinose or pruinose lateral cortices: irregularly paraplectenchymatous, 40-60 µm thick; syncortex: 10-30 µm thick; eucortex: upper layer yellowish to reddish brown, hyaline below and 20-30 µm thick algal layer: even becoming thin and uneven in development through penetration of hyphae spreading algal cells, usually pushed to sides of the areoles with the expansion of the apothecium, few to no algal cells beneath the apothecia medulla: white, prosoplectenchymatous attachment: broad without forming a stipe Apothecia: one or more per areole, often deeply immersed disc: dark brown, smooth or rough, pruinose if thallus pruinose parathecium: indistinct, up to 20 µm thick epihymenium: reddish brown, conglutinated, 10-15 µm thick hymenium: hyaline, 60-100 µm tall; paraphyses: c. 2 µm wide at base, apices ±expanded, moderately branched subhymenium: hyaline, 20-30 µm thick; hypothecium: up to 20 µm thick asci: clavate, c. 65 x c. 20 µm, 100+-spored ascospores: hyaline, simple, short and broadly ellipsoid, 3 x 2-2.2 µm but appearing wider and longer due to a mucilaginous sheath, visible inside ascus and outside around mature spores, especially in K or IKI Pycnidia: not seen Spot tests: UV-, cortex C+ red, KC+ red and/or medulla, reaction strong to uneven and occasionally spot tests are negative (a specimen from the An-za-Borrego Desert) Secondary metabolites: gyrophoric acid. Substrate and ecology: on acidic or carbonate rocks World distribution: southwestern North America (Nevada) Sonoran distribution: Arizona, southern California (Anza-Borrego Desert), and Baja California. Notes: Pruinose specimens of A. nevadensis look like some forms of A. strigata, which are C- and have longer spores without discernible mucilage. The type is from Reno, Nevada (UPS!). Several specimens were seen from Arizona (ASU) that were epruinose and lacked fissuring but otherwise had the same internal anatomy and distinctive spores. Epruinose specimens having no fissuring had longer, flatter elongate areoles with more than one apothecium per areole and may possibly represent an intraspecific morphotype. Golubkova (1983) determined specimens from Russia as A. nevadensis, but this interpretation is apparently based on her reading of Magnusson's publication and not on the holotype. It is probably a different species. There may also be other pruinose C+ species in western North America that are undescribed and lack short broad spores with a mucilaginous layer.