Thallus: orbicular to irregular, firmly adnate, sometimes imbricate, up to 3 cm across lobes: convex to plane, up to 1 mm broad, rarely overlapping, ± truncate, eciliate upper surface: whitish gray to gray, shiny, white maculate, lobe tips often brownish, particularly old herbarium material upper cortex: paraplectenshymatous, medulla: white lower cortex: paraplectenchymatous, sometimes indistinctly but the lowermost cells always short and thick-walled lower surface: white to brownish or pinkish yellow, shiny, with few concolorous rhizines Apothecia: ± abundant, up to 2 mm diam.; margin thick; disc: black; ascospores: brown, 1-septate, Pachysporaria to Physcia type, (15-) 16-19 (-21) x (8-) 9-11 (-14) µm Pycnidia: common, immersed conidia: subcylindrical, 4-6 x 1 µm Spot tests: cortex and medulla K+ yellow, C-, KC-, P+ yellow, Secondary metabolites: cortex with atranorin; medulla with atranorin, zeorin and some unidentified triterpenes. Substrate and ecology: growing on rocks in exposed habitats, including the seashore and arid habitats World distribution: known from Brazil, Paraguay, Peru and Uruguay Sonoran distribution: intermediate elevations in southern Arizona, Chihuahua, Sonora and Baja California Sur. Notes: Physcia convexa is easily recognized by the convex, usually well separated lobes with truncate tips, the presence of apothecia and the pale, often pinkish underside. It is similar to P. phaea but the latter has less convex lobes with crenulate and widening tips and different lower cortex. Small specimens of P. convexa may be mistaken as P. convexella but are easily separated by the K- medulla in P. convexella. P. cinerea is more narrow lobed and has different upper surface and chemistry.