Squamules: up to 5 mm wide, rounded, adnate, dispersed to adjacent, usually concave; upper surface: castaneous brown, shiny, epruinose, smooth or sparingly fissured; margin: concolorous with upper side, down-turned, entire or lobed; upper cortex: up to 60-80 μm thick, composed of thin-walled hyphae with round lumina, not containing crystals of lichen substances or calcium oxalate; medulla: containing crystals of lichen substances but no calcium oxalate; lower cortex: of mainly periclinally oriented hyphae, not containing calcium oxalate; lower surface: white to pale brown; Apothecia: up to 1 mm diam., marginal, immarginate even when young, black, epruinose; ascospores: 8-13 x 5-7 μm; Pycnidia: laminal, immersed; conidia: bacilliform, 5-7 x 1 μm; Spot tests: upper cortex K-, C-, KC-, P-; medulla K-, C+ red, KC+ red, P-; Secondary metabolites: gyrophoric acid and trace of lecanoric acid.
The species resembles some epruinose, concave forms of P. russellii but differs in having black, marginally attached apothecia and deeper castaneous brown squamules, in the absence of calcium oxalate from the medulla, and in the presence of gyrophoric acid as the only lichen substance in the thallus. In P. russellii the apothecia are dark reddish brown to dark brown and attached laminally to submarginally to the squamules, and calcium oxalate and almost always norstictic acid, sometimes also a trace of gyrophoric acid, are present in the medulla. Psora nitida also resembles P. californica in the shiny, castaneous brown squamules containing gyrophoric acid, but differs in the more isodiametrical shape of the squamules which usually have a distinct central depression, in the marginally attached apothecia, absence of bourgeanic acid, and in the location of the gyrophoric acid in the thallus. In P. nitida this substance is restricted to the medulla, in P. californica to the upper cortex.
Baja California del Norte.
On soil in Vizcaino subdivision of Sonoran desert, often in hillsides, up to 400 m alt.
Psora californica, Psora russellii.