Thallus: crustose, rimose-areolate, forming an irregularly rounded patch usually 2-5 cm across and up to 0.4 mm thick; prothallus: thin, black, sometimes visible between the areoles or along the thallus margin especially at the juncture of a different thallus, areoles: usually contiguous, becoming almost bullate, plane to convex, ecorticate surface: white to grayish white, cream-colored or pale yellow, smooth, shiny to dull, esorediate Apothecia: immersed in center of the areoles, 1-3 per areole, up to 0.5 mm in diam. disc: black, flat to slightly convex, sometimes with a dusting of white pruina margin: usually flat and continuous with the areole surface, up to 0.7 mm wide, without a parethecial ring parathecium: yellowish ochre, 10-20 µm wide epihymenium: dark olive green to bluish green, 10-15 µm thick hymenium: hyaline, 35-55 µm tall; paraphyses: unbranched, rarely anastomosing, below 1.5-2 µm wide, terminally globose up to 3.5 µm wide; subhymenium: hyaline; hypothecium: hyaline asci: clavate, I+ blue, c. 8-spored ascospores: hyaline, simple, ellipsoid, (7-)9-14 x 4-6.5(-7.5) µm Pycnidia: immersed conidia: hyaline, filiform, 10-16 x c. 0.8 µm Spot tests: cortex K+ yellow, C-, KC-, P+ yellow; medulla K-, C-, KC-, P- Secondary metabolites: upper cortex with atranorin and chloroatranorin, medulla with confluentic (major) and 4O-methylmicrophyllinic (minor) acids. Substrate and ecology: on a range of different acidic rocks in open to partially shaded habitats at intermediate elevations World distribution: temperate regions of North and South America, Africa, eastern Asia, Australasia and Oceania and extending towards the tropics in mountainous regions Sonoran distribution: common throughout the region at intermediate elevations in Arizona, Chihuahua, Sonora, Sinaloa and Baja California Sur. Notes: Superficially L. oreinoides is similar to some species of Buellia, which can be readily separated by their brown, 1-septate spores. At first glance L. oreinoides is also similar to L. subimmersa (below), but the latter species has an even flatter thallus surface, brown disc, somewhat smaller spores and a different medullary chemistry. Lecanora oreinoides differs from similar lecideoid species with white or pale yellow thalli by having apothecia mostly under 0.5 mm in diam. and by lacking usnic acid.