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DescriptionSquamules: up to 5 mm wide, elongate, adnate to imbricate, weakly concave to weakly convex; upper surface: greenish brown to medium brown, dull, epruinose or pruinose near the margin, sparingly fissured; margin: concolorous with upper side, straight or up-turned, crenulate to lobed; upper cortex: up to 100 µm thick, composed of thick-walled hyphae with rather angular lumina, not containing crystals of lichen substances or calcium oxalate; medulla: containing lichen substances but no calcium oxalate; lower cortex: of mainly periclinally oriented hyphae, containing orange crystals (polarized light!) but not calcium oxalate; lower surface: orange brown, K+ red; Apothecia: up to 1.5 mm diam., laminal, convex and immarginate even when young, dark brown, epruinose; ascospores: ellipsoid, 9.5-11.5 x 4.5-7 µm; Pycnidia: not seen; Spot tests: upper cortex K-, C-, KC-, P-; medulla K-, C+red, KC+ red, P-; lower cortex K+ red, C-, KC-, P-; Secondary metabolites: gyrophoric acid and a series of undetermined anthraquinones.; Substrate and ecology: in crevices of rock in open habitats, mainly in conifer forests, at 1030-1980 m; World distribution: only known from California; Sonoran distribution: rare in the mountains of southern California.; Notes: This species was treated as a chemotype of P. globifera by Timdal (1984a) and of P. californica by Timdal (1986). It is morphologically most similar to the former, and chemically most similar to the latter. It differs from P. globifera in having slightly paler and duller squamules with fewer fissures in the upper cortex, and in containing gyrophoric acid in the medulla and anthraquinones in the lower cortex. It differs from P. californica in having paler, duller, not down-turned, more crenulate, and more imbricate squamules with more fissures in the cortex; in containing anthraquinones in the lower cortex; and in lacking bourgeanic acid. Psora californica and P. hyporubescens are largely sympatric, but do not show altitudinal overlap: the former is known from 270-980 m in southern California (at 1250 m on Isla Guadalupe), the latter is known from 1030-1980 m.