Squamules: up to 6 mm wide, elongate, adnate and dispersed to adjacent or imbricate, weakly concave to weakly convex; upper surface: castaneous brown, shiny, epruinose, smooth or sparingly fissured; margin: concolorous with upper side, often slightly down-turned, entire, crenulate or lobed; upper cortex: up to 140 μm thick, composed of thick-walled hyphae with angular lumina, containing crystals of lichen substances but no calcium oxalate; medulla: not containing crystals; lower cortex: of mainly periclinally oriented hyphae, not containing calcium oxalate; lower surface: medium brown, K-; Apothecia: up to 1.5 mm diam., laminal, immarginate or marginate when young and later immarginate, dark brown to black, epruinose; ascospores: 12-14 x 5-7 μm; Pycnidia: laminal, immersed; conidia: bacilliform, 5-7 x 1 μm; Spot tests: upper cortex K-, C+ red, KC+ red, P-; medulla K-, C-, KC-, P-; Secondary metabolites: bourgeanic acid, gyrophoric acid, and trace of lecanoric acid.
Psora californica differs morphologically from P. globifera and P. hyporubescens mainly in having squamules with a straight or usually slightly down-turned margin, a more shiny upper side without or with only a few fissures, and in containing lichen substances in the thallus. In P. globifera and P. hyporubescens the margin of the squamules is usually slightly up-turned and the upper side usually provided with several fissures in the cortex. The hyphae in the upper cortex are usually more thick-walled in P. californica than in P. globifera. Psora californica contains gyrophoric acid in the upper cortex and bourgeanic acid in the thallus (not further located), P. hyporubescens contains gyrophoric acid in the upper cortex and anthraquinones (K+ purple) in the lower cortex, and P. globifera lacks lichen substances in the thallus.
Psora nitida forms more isodiametrical squamules, usually with a central depression, marginally attached apothecia, and contains gyrophoric acid in the medulla (not in the upper cortex).
West coast of North America.
On soil and in crevices of rock, in open habitats in the lowlands, up to 980 m alt. in California, at 1250 m alt. on Isla Guadalupe.
Psora globifera, Psora hyporubescens, Psora nitida.
