Squamules: up to 10 mm wide, elongate, ascending, concave to weakly convex; upper surface: olivaceous or reddish brown to medium brown, dull, epruinose or partly pruinose, smooth or sparingly fissured; margin: usually white, down-turned to up-turned, entire or lobed; upper cortex: up to 55-140 μm thick, composed of thick-walled hyphae with angular lumina, containing crystals of lichen substances but no calcium oxalate; medulla: containing crystals of lichen substances but no calcium oxalate; lower cortex: of anticlinally oriented hyphae, containing calcium oxalate; lower surface: white to medium brown; Apothecia: up to 2 mm diam., laminal, immarginate even when young, dark brown to black, epruinose; ascospores: 10-14 x 5-7 μm; Pycnidia: laminal, immersed; conidia: bacilliform, 6-9 x 1 μm; Spot tests: upper cortex and medulla K-, C+ red, KC+ red, P-; Secondary metabolites: gyrophoric acid and trace of lecanoric acid.
The species is usually easily distinguished by the large, more or less white-edged, ascending squamules. The type of lower cortex indicates that the species may be more closely related to P. rubiformis and P. tenuifolia than to the morphologically and chemically more similar P. californica. A chemical strain containing anthraquinones in the lower cortex is known from northern California and Idaho.
Japan and western North America.
On soil or rock, usually in rock crevices in some shade, mainly in conifer forests and above tree line.
Psora tenuifolia.
