Thallus: rimose- to verrucose-areolate; areoles: 0.5-2.5 mm in diam., plane to subconvex, thick upper surface: whitish to whitish gray, rough, dull, scarcely to abundantly grayish or whitish pruinose Ascomata: urceolate, sessile, slightly pruinose, up to 2.5 mm in diam.; disc: blackish, concave; proper exciple: up to 80 µm thick; hymenium: 110-180 µm high asci: subclavate to cylindrical, 4-8-spored ascospores: brown, muriform, broadly ellipsoid, 20-38 x 9-17 µm; transverse septa 3-6; longitudinal septa 1-2 per transverse segment Pycnidia: immersed conidia: bacilliform, 4-6 x 1.0-1.5 µm Spot tests: K+ yellow to red, C+ red, KC-, P-, UV- Secondary metabolites: diploschistesic and lecanoric acids (both major) and orsellinic acid (minor). Substrate and ecology: on soil in open habitats World distribution: subcosmopolitan in open habitats with Mediterranean to arid climate Sonoran distribution: common in semi-arid exposed habitats and coastal areas at 5-250 m (and up to 800 m) in Baja California and southern California, and in open bushlands or open pine forests at an elevation of c. 1600-1800 m in Arizona and Chihuahua. Notes: Diploschistes diacapsis is a terricolous species which is readily identified by the K+ yellow to red reaction of the thallus due to the presence of diploschistesic acid as major constituent, the whitish pruinose thallus, (4-) 8-spored asci, and the ascospore size. A similar species is D. muscorum which differs in having always 4-spored asci, being a juvenile parasite on Cladonia spp., and having a thinner thallus. North American records of D. ocellatus belong to D. diacapsis. Diploschistes ocellatus does not occur in the western Hemisphere, it is easily distinguished from D. diacapsis by the lecanoroid ascomata and the presence of norstictic acid.