Thallus: rimose-to verrucose-areolate; areoles: 0.4-1.5 mm in diam., plane to subconvex, thin or thick upper surface: greenish or brownish gray, smooth, shiny or dull, epruinose Ascomata: urceolate, sessile, slightly pruinose, up to 2.0 mm in diam.; disc: blackish, concave; proper exciple: up to 75 µm thick; hymenium: 100-140 µm high asci: subclavate to cylindrical, (4-) 8-spored ascospores: brown, muriform, ellipsoid, 25-40 x 10-20 µm; transverse septa 4-7, longitudinal septa 1-3 per transverse segment Pycnidia: immersed conidia: bacilliform, 4-6 x 1.0 µm Spot tests: K- or + yellow to red, C+ red, KC-, P-, UV- Secondary metabolites: diploschistesic acid (major or absent), lecanoric acid (major), and orsellinic acid (minor). Substrate and ecology: usually on siliceous rocks World distribution: cosmopolitan in relatively open habitats in Mediterranean, temperate and polar regions and extending to high altitudes in the tropics Sonoran distribution: common, at an elevation of c. 0-2700 m in Arizona, Baja California, California and Chihuahua. Notes: The saxicolous Diploschistes scruposus is characterized by an epruinose thallus and ureolate ascomata. A similar species is D. muscorum and the differences are discussed under that name.