Thallus: squamulous-areolate, 1-5(-10) cm in diam., 0.1-0.5(-1) mm thick areoles: usually round, sometimes angular or irregular, flat or slightly convex, (0.2-)0.5-1.2(-2.2) mm in diam., ±dispersed or sometimes contiguous and separated by ±large cracks prothallus: absent surface: chalky white (from dense pruina) to gray or green-gray or buff or light brown, dull photobiont: chlorococcoid, cells ±round, 5-17(-22) µm in diam. Apothecia: aspicilioid, common, (0.1-)0.2-0.5(-0.8) mm in diam., 1-2(-3) per areole, round, rarely angular or elongated disc: black, concave or sometimes flat, usually with a white pruina thalline margin: flat to usually slightly elevated (areoles then resembling small volcanos!), rarely prominent, often forming a white rim exciple: (15-)20-50(-100) µm wide, I-, or rarely partly I+ blue; uppermost cells brown, ±globose, (4-)5-6(-8) µm in diam. epihymenium: green to olive, olive-brown or brown, with crystals, N+ green to blue-green, K+ brown to green-brown hymenium: hyaline, I+ persistently blue or sometimes partly turning yellow-green, (100-)110-170(-210) µm tall paraphyses: submoniliform, rarely moniliform, with (0-)1-2(-4) upper cells ±globose to subglobose or sometimes subcylindrical to cylindrical, (3-)4-6 µm wide, in lower part (1-)1.5-2(-2.5) µm wide, slightly branched and anastomosing subhymenium and hypothecium: pale, I+ persistently blue or sometimes partly turning yellow-green, together (20-)30-60(-100) µm thick asci: clavate, (65-)70-120(-135) x 20-30(-32) µm, (1-)2-6(-7)-spored ascospores: hyaline, simple, globose to subglobose, (16-)18-28(-35) x (14-)17-24(-28) µm Pycnidia: uncommon, 1(-2) per areole, immersed, (90-)100-130 µm in diam., with a black, punctiform ostiole, sometimes almost covered by a white pruina or surrounded by a white rim, 50-80 µm in diam. conidia: filiform, straight or slightly curved,, (5-)6-8.5-10(-11) x 0.8-1(-1.3) µm Spot tests: cortex and medulla I-, K-, P-, C- Secondary metabolites: usually with aspicilin, rarely lacking secondary metabolites. Substrate and ecology: on calcareous rocks World distribution: Eurasia and North America Sonoran distribution: Arizona, southern California and Baja California Sur, at 150-2500 m. Notes: Aspicilia contorta is characterized by a white to gray or green-gray thallus with ±dispersed areoles, the lack of a prothallus, submoniliform paraphyses, asci with 2-6 globose to subglobose spores, short conidia and the presence of aspicilin. Two other species with aspicilin and 2-6 globose to subglobose spores per ascus, A. desertorum and A. praecrenata, occur in the Sonoran area. Aspicilia desertorum differs from A. contorta by its brown and ±thick thallus; A. praecrenata, by being terricolous and having apothecia with a ±crenulate thalline margin. Aspicilia calcarea (L.) Mudd. has not been found in the Sonoran area, although the name has frequently been used for North American material. This European species differs from A. contorta by its contiguous, rimose-areolate thallus, delimited by a prothallus, and the lack of aspicilin. The report of Lecanora calcarea (=Aspicilia c.) from southern California by Hasse (1912) proved to be Aspicilia contorta. DNA (ITS) from one specimen of Aspicilia contorta ssp. contorta (Knudsen 837) from California agrees fairly well with sequences from European material of this subspecies (unpublished observation). Other specimens from California (Hasse 2420, Wetmore 50771) and Mexico (Baja California Sur; Nash 29602 & 29615) are morphologically similar to this subspecies. Specimens from Arizona sometimes have contiguous, not dispersed areoles, remind one of Aspicilia contorta ssp. hoffmanniana Ekman & Fröberg, but further DNA studies of such specimens are needed in the future.