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DescriptionThallus: continuous to fissured, with thin to moderately thick verrucae; margins: definite, entire to zoned; upper surface: whitish gray to yellowish gray, epruinose; soredia: in verrucae, 0.5-4.5 mm in diam., lecanorate; Apothecia: no fertile specimens seen; Pycnidia: not seen; Spot tests: K-, C-, KC-, P-, UV-; Secondary metabolites: allopertusaric (major) and dihydropertusaric (minor) acids.; Substrate and ecology: on hardwoods or conifers, such as Pseudotsuga, at 2000 to 2600 m; World distribution: widely distributed in the Northern Hemisphere, very common in Europe, restricted in North America to the SW and central Mexico; Sonoran distribution: restricted to montane areas of southern California.; Notes: This species is readily identified by the large disciform soralia, the thick thallus often with zonate margins and the lack of phenolic compounds. The soralia are in fact sorediate verrucae, but these are very rarely fertile, and no material from the study area examined contained spores or asci. Pertusaria albescens may be confused with P. amara when poorly developed. However, the two species are easily distinguished by the bitter taste or KC + violet reaction of the thallus due to the presence of picrolichenic acid in the latter species.