Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.

Thallus: crustose, episubstratic, large, up to 15 cm in diam., 0.1-0.8 mm thick, continuous or rimose-areolate surface: gray, or white, not sorediate anatomy: medulla hyphae euamyloid Apothecia: up to 40 per cm², up to 2.2 mm in diam., semi-immersed or sessile, slightly constricted at base disc: black, plane to rarely strongly convex to weakly convex, usually grayish pruinose margin: distinct, sometimes becoming excluded exciple: black or dark brown, up to 175 µm wide, without crystals, with parallel-radiate hyphae; hyphae c. 4 µm wide epihymenium: brown or brownish yellow hymenium: hyaline, 70-100(130) µm tall, I+ blue; hypothecium: blackish brown asci: clavate to subcylindrical, 8-spored ascospores: broadly ellipsoid or ellipsoid, (12-)15-20-(25) µm long, 6-8(-9.5) µm wide; wall thick and smooth (multi-layered, halonate) conidia: bacilliform, 8-12 x c. 1 µm Spot tests: medulla: K- or K+ yellow (carbon dioxide development, rarely yellow solution), C-, P- or rarely + reddish yellow Secondary metabolites: 2'-O-methylmicrophyllinic acid, 2'-O methylperlatolic acid, confluentic acid, rarely additional stictic acid. Substrate and ecology: on non-calciferous rock or calciferous rock World distribution: Europe and North America Sonoran distribution: not known for sure in the Sonoran area but it may occur as it is found on coastal rocks farther north in California.