Thallus: peltate, scattered individually, sometimes lobed (rarely polyphyllous), up to 12 mm in diam.; margins: downrolled, not undulate upper surface: tan-olive-green to dark olive-brown, dull to shiny soredia: farinose, black, marginal (rarely laminal), in elongated soralia upper cortex: lacking but with a yellow to brownish epinecral layer (5-10 µm thick) medulla: composed of loosely interwoven hyphae (cells: elongated, 1.5-3 µm thick); algal layer: clearly delimited, 70-150 µm thick lower cortex: 18-90 µm thick, proso- to paraplectenchymatous, hyphae often anticlinally arranged; cells: globose to elongated, 3-8 µm thick lower surface: paler than the upper surface, attached by an umbilicus Apothecia: rare, many per squamule, immersed; disc: punctiform to widely expanded, 0.1-0.9 mm diam.; epihymenium: yellowish brown or pinkish, K-; hymenium: I+ wine-red, 105-220 µm high asci: clavate to obclavate; wall: I+ slightly blue and more strongly blue after pretreatment with K, 32-100-spored ascospores: ellipsoid to bacilliform, 6-9 x 3-4.8 µm Pycnidia: immersed, chambered, up to 150 µm diam. conidia: fusiform, 3-3.5 x 1-1.5 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on acidic rocks in deserts and other open, arid habitats World distribution: throughout arid and semi-arid regions on all continents and extending into temperate regions of North America, Eurasia and Australasia Sonoran distribution: desert to mountain areas of Arizona, southern California, Sonora, Sinaloa, Chihuahua Baja California and Baja California Sur.