Thallus: crustose, thin to moderately thick, verruculose, rarely verrucose verruculae: usually weakly developed surface: yellowish gray to yellowish white, rugose, continuous, epruinose, with a distinct margin, esorediate Apothecia: lecanorine, sessile, broad, 1-3(-4) mm in diam., flat disc: light orange to light orange-yellow or yellowish pink, usually rugose but epruinose, rarely smooth, sometimes with a disc-colored excipular ring adjacent to the disc, but lacking discoid tissue, K-, C+ red, KC-, P- margin: concolorous with thallus, rarely light orange, thick, usually even, prominent, smooth to more frequently rough, K-, C+ red, KC+ red, P- amphithecium: often containing small crystals, radiate; cortex: radiate or not, +differentiated, 20-40 µm thick, inspersed exciple: relatively thin, distinct or not, (15-)30-50(-70) µm; algal layer: forming a conspicuous, complete layer below the hypothecium, often also in the margin just internal to the cortex hymenium: 180-280 µm tall; hypothecium: thick, 70-90 µm asci: 8-spored ascospores: hyaline, simple, ellipsoid, (35-)40-58 x 20-31 µm Pycnidia: not seen Spot tests: thallus cortex K-, C+ red, KC+ red, P-; medulla K-, C-, KC-, P-; all tissues: UV- Secondary metabolites: gyrophoric, lecanoric (+trace) and 4-O-demethylmicrophyllinic (+trace) acids (constant), olivetoric (+60% of specimens seen by Brodo (1991)), and several unidentified fatty acids. Substrate and ecology: on bark of mainly deciduous trees (e.g. Quercus, Rhamnus, Alnus) rarely conifers (e.g. Pseudotsuga), in oak forests from 0-1550 m World distribution: west coast of North America, from the Queen Charlotte Islands to southern California, plus Asia, Brazil and western Australia Sonoran distribution: central to coastal southern California and Arizona. Notes: Ochrolechia subpallescens is distinguished by its production of olivetoric and 4-O-demethylmicrophyllinic acids in most specimens, and by its short hymenium and small spores.