Squamules: up to 6 mm wide, elongate, imbricate, weakly concave to weakly convex; upper surface: light brown or medium brown, dull, epruinose or partly pruinose, smooth or sparingly fissured; margin: concolorous with upper side or white, down-turned or straight, entire or lobed; upper cortex: up to 60-120 μm thick, composed of thin-walled hyphae with round lumina, not containing crystals of lichen substances, sometimes containing calcium oxalate; medulla: not lichen substances, often containing calcium oxalate; lower cortex: of mainly periclinally oriented hyphae, not containing calcium oxalate; lower surface: white to medium brown; Apothecia: up to 1.5 mm diam., laminal, convex and immarginate even when young, medium brown, epruinose or white or yellow pruinose; ascospores: 8-12 x 6-8 μm; Pycnidia: unknown; Spot tests: upper cortex and medulla K-, C-, KC-, P-; Secondary metabolites: none.
Psora tuckermanii shows an extensive morphological variation, and may be confused mainly with P. himalayana, P. luridella, P. pseudorussellii, and P. russellii; see these species for discussions.
Western North America.
On soil and rock in open habitats, mainly in pinyon-juniper woodland, conifer forests, and Great Basin desert scrub.
Psora himalayana, Psora luridella, Psora pseudorussellii, Psora russellii.