Squamules: up to 6 mm wide, rounded, adnate and dispersed to adjacent or imbricate, weakly concave to weakly convex; upper surface: orange to bright red or rose, dull or shiny, epruinose or partly to entirely pruinose, smooth or sparingly fissured; margin: concolorous with upper side or white, straight or slightly up-turned, entire or often weakly crenulate (especially when young); upper cortex: up to 80-120 μm thick, composed of thin-walled hyphae with round lumina, containing crystals of calcium oxalate but no lichen substances; medulla: containing crystals of calcium oxalate, sometimes also lichen substances; lower cortex: absent or poorly developed; lower surface: white to pale brown; Apothecia: up to 2 mm diam., marginal, immarginate even when young, black, epruinose or white or yellow pruinose; ascospores: 11-18 x 6-8 μm; Pycnidia: laminal, immersed; conidia: bacilliform, 6-7 x 1 μm; Spot tests: upper cortex and medulla K-, C-, KC-, P-; Secondary metabolites: none, norstictic acid, or hyposalazininc and hypostictic acid.
Pink to reddish squamules are diagnostic for P. crenata, P. decipiens and P. saviczii; see those species for discussions.
Specimens containing hyposalazinic and hypostictic acids occur in Europe and North America; these tend to have more pink coloured squamules. In the Arctic and in mediterranean Europe specimens with a high concentration of norstictic acid are common. There are other chemical strains in Australia and southern Africa.
Cosmopolitan: Africa, Asia, Australia, Europe, North America, and South America.
On more or less calciferous soil and crevices of rock in open habitats, from deserts to arctic-alpine habitats.
Psora crenata, Psora saviczii