Thallus: areolate or verruculate, dispersed or indeterminate and up to 4 cm wide verrucae or areoles: round to very irregular and flattened, 0.3-0.7(-2) mm in diam., rarely up to 1 mm thick, contiguous or scattered; rim: ±down-turned upper surface: pale yellowish brown to dark brown, dull, plane to convex, smooth, usually faveolate with minute pits around apothecia, or wrinkles and folds, becoming rugulose, pruinose or not upper cortex: paraplectenchymatous, 20-30(-35) µm thick; cells: round to angular, 3-5 µm wide; eucortex: upper layer pale brown and c. 10 µm thick, lower layer hyaline algal layer: thickness extremely variable, sometimes filling most of interior of verrucae medulla: white, prosoplectenchymatous, sometimes reduced to area around attachment and always continuous with it lower cortex: undeveloped when broadly attached or well developed when stipitate, cortical layer 20-30 µm thick, with cells 3-5 µm wide lower surface: black but sometimes white or dirty white attachment: broad or narrow with rhizohyphae up to 5 µm thick, rarely thickening and elongating in older squamules forming a very short stipe in mesic microhabitats Apothecia: one or more per squamule usually without cortical fissures between them and sometimes several small apothecia eventually merging; but some verrucae sterile with a cup of an apothecium formed in thallus by true exciple but empty disc: dark brown, plane, epruinose or pruinose (sometimes heavily) parathecium: 10-20 µm thick, often widening and forming a ring around the disc epihymenium: light to dark brown; ±10 µm thick hymenium: hyaline, coherent, 100-135 µm tall; paraphyses: 1.5-2.4 µm wide at base with unexpanded apices often with dark pigmented hoods in gelatinous pigmentation zone subhymenium: hyaline or golden, 10-30 µm thick; hypothecium: c. 10 µm thick asci: cylindrical, as tall as the hymenium, broadening to c. 15 µm, 100+-spored ascospores: hyaline, simple, ellipsoid, 3.9-5(-7.1) x 1-1.9(-2.5) µm, usually reaching its width first and then elongating Pycnidia: not seen Spot tests: UV-, cortex C+ red, KC+ red but some specimens seen from Verdugo Mountains and Matilija Canyon in southern California are C- and TLC is necessary for identification Secondary metabolites: gyrophoric acid (major), lecanoric acid (minor), 3-hydroxygyrophoric acid (trace), methyl lecanorate (trace) (HPLC, J.A. Elix, pers comm.) Substrate and ecology: on soil, sandstone, rhyolite or decomposing granite at sites usually with eastern and western exposures, sometimes growing on other lichens when on soil (Aspicilia glaucopsina and Acarospora thelococcoides) World distribution: South and North America Sonoran distribution: Arizona, southern California, Baja California, Baja California Sur, and Sonora. Notes: Some highly pruinose specimens of A. obpallens resemble pruinose A. veronensis; the pruinosity is probably due to the desert environment. If the C reaction is negative, the two species can be easily confused and TLC is needed to separate them. Magnusson and Zahlbruckner restricted A. obpallens to specimens on soil; they applied the other names cited above to specimens on rock. Specimens from Coyote Ridge above the campus of the University of California in Riverside, California, are extremely rugulose and up to 4 mm in diameter, represent either an extreme variation, or a population over-stimulated by nitrate deposition, but are tentatively included in A. obpallens. Two other species with gyrophoric acid were seen from outside Sonoran study area: a taxon from New Mexico on sandstone and A. fuscescens H. Magn. on sandstone in Utah and New Mexico. Some specimens of A. fuscescens can be confused with A. obpallens but A. fuscescens is never faveolate and often forms an areolate thallus similar to Sarcogyne desolata.