Squamules: up to 3 mm diam., elongated, adnate or partly ascending, contiguous or irregularly imbricate. Upper side: medium brown to castaneous brown, dull to somewhat shiny, epruinose or more rarely somewhat pruinose, almost without fissures; margin: concolorous with the upper side or somewhat paler, usually straight, deeply incised to lobate; underside: pale brown to medium brown. Upper cortex: 35-80 μm thick, composed of rather thick-walled hyphae with more or less angular lumina, gyrophoric acid present in the stainable layer. Medulla: containing gyrophoric acid. Lower cortex: well developed, composed of mainly periclinally oriented hyphae with thread-like lumina, lacking crystals. Apothecia: up 1.2 mm diam., attached laminally to the squamules, usually simple, plane to weakly convex when young, later usually becoming weakly to moderately convex or rarely strongly convex, medium brown to dark brown, dull, epruinose or rarely faintly yellow pruinose. Ascospores: 9-14 x 5-7 μm. Pycnidia not seen. Thallus chemistry: gyrophoric acid and trace of lecanoric acid.
The species is closely related to P. pacifica and differs mainly in having more adnate, less frequently pruinose squamules and a thicker lower cortex, and lacking the undetermined substance usually occurring in P. pacifica. The two species also differ in geographical distribution.
Western North America.
The species is terricolous, occurring in montane areas below or at the timberline, sometimes in the alpine region or at lower altitudes.
Psora pacifica.
