Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2002. Lichen Flora of the Greater Sonoran Desert Region. Vol 1.
Thallus: subfoliose, forming rosettes to 2-3 cm wide, resting on a distinct bluish black hypothallus upper surface: blue-gray, distinctly pruinose Apothecia: common, particularly centrally, flat brownish with distinct crenulate thalline margin; exciple: subparaplectenchymatous, 30-40 µm thick; hymenium: primarily hyaline but brown above, partially I+ blue (in vicinity of the asci) asci: clavate, without inner apical, amyloid structures, 8-spored ascospores: simple, colorless, ellipsoid 12-14 x 8-9 µm Spot tests: thallus K-, C-, KC-, P+ orange Secondary metabolites: pannarin. Substrate and ecology: on rocks in the Sonoran region, often corticolous elsewhere, in misty cool temperate forests World distribution: The mountains of South and Central America and the Pacific coast of North America to Queen Charlotte Islands Sonoran distribution: rare, only collected once, in Tomochic valley in the Sierra Madre Occidental (Chihuahua), on a rock outcrop in a pine-oak forrest, about 2000 m., but possibly more common. Notes: It is a long misunderstood species, often confused with the larger, more leafy P. rubiginosa, which has a different chemistry and larger spores (see below).