Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2002. Lichen Flora of the Greater Sonoran Desert Region. Vol 1.
Thallus: squamulose to subfoliose, orbicular, up to 5 cm broad, flat and thin (to 100 µm) lobes: often delicately incised, with marginal lobules upper surface: uniformily brownish gray Apothecia: common, up to 2 mm diam.; disc: brownish and distinct, with a conspicuous, crenulate thalline margin; exciple: subparaplectenchymatous, 30-40 µm thick; hymenium: up to 100 µm, I+ blue only in the vicinity of the asci asci: clavate, without any internal amyloid apical structures, 8-spored ascospores: simple, colorless, subglobose, 9-12 x 8-11 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on trees in warm, temperate deciduous forests World distribution: only known from eastern North America to Central America Sonoran distribution: rather common in the oak forests of SE Arizona, Sonora and Chihuahua. Notes: Previously it was confused with P. rubiginosa which is a larger, grayer species with a P+ orange thallus and much larger, more ellipsoid spores.