Squamules: up to 3 mm wide, elongate, adjacent or partly ascending, weakly concave to plane; upper surface: medium brown, dull, becoming densely pruinose, smooth; margin: concolorous with upper side, often slightly up-turned, not pruinose, crenulate or lobed; upper cortex: up to 140 μm thick, composed of rather thick-walled hyphae with somewhat angular lumina, containing crystals of calcium oxalate but no lichen substances; medulla: containing lichen substances but no calcium oxalate; lower cortex: poorly developed, composed of mainly periclinally oriented hyphae, not containing calcium oxalate; lower surface: pale brown; Apothecia: up to 1.5 mm diam., laminal, convex and immarginate even when young, medium brown to reddish brown, epruinose; ascospores: 11-15 ´ 5.5-7 μm (n=20); Pycnidia unknown; Spot tests: upper cortex K-, C-, KC-, P-, medulla K-, C-, KC-, P+ red; Secondary metabolites: pannarin.
The species is recognized by the densely pruinose squamules with an up-turned, epruinose margin, and by the presence of pannarin which is unique in Psora.
California and Baja California del Norte.
On soil in open habitats, in Vizcaino subdivision of Sonoran Desert and in Californian coastal scrub, up to 230 m alt.
Psora californica, Psora peninsularis.
