Thallus: rimose-areolate; areoles: 0.3-1.5 mm in diam., plane, thin upper surface: whitish gray, smooth, shiny or dull, epruinose Ascomata: perithecioid, immersed to semi-immersed, up to 1.8 mm in diam.; disc: blackish, plane; proper exciple: up to 90 µm thick; hymenium: 100-140 µm high asci: subclavate, (6-) 8-spored ascospores: brown, muriform, broadly ellipsoid, 16-32 x 10-20 µm; transverse septa 3-6, longitudinal septa 1-4 per transverse segment Pycnidia: not seen Spot tests: K-, C-, KC-, P-, UV- Secondary metabolites: none observed. Substrate and ecology: on siliceous rocks World distribution: subcosmopolitan in relatively open habitats. Mainly in semi-arid and arid regions, but also extending into the temperate zone Sonoran distribution: rare, in Baja California at 150 m and Chihuahua at 1600 m. Notes: Diploschistes euganeus is characterized by the broadly ellipsoid ascospores and the thin thallus lacking secondary metabolites. The distinction from the similar D. arabiensis is discussed under that name.