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DescriptionLife habit: lichenized, not lichenicolous; Thallus: crustose, areolate; prothallus: usually present, black, dendritic; areoles: mainly angular (not peltate), flat to weakly convex, usually contiguous, 0.2-0.5 mm in diam.; surface: gray-brown to brown or occasionally red-brown; cortex: thin, 5-15 µm thick, +with a thin epinecral layer up to 8 µm thick; medulla: white, I+ blue; Apothecia: round to angular, 0.3-1 mm in diam.; disc: black, remaining +flat, usually epruinose; margin: +immarginate or with thin persistent margin; exciple: K+ red; epihymenium: carbonaceous incrusted, in section brown-black, opaque, K+ red or reddish violet; hymenium: hyaline, 70-130 µm tall; paraphyses: capitate, with dark tips; hypothecium: violet-brown or olive-black, K-; ascospores: hyaline or sometimes greenish brown with age, (1-)3(-5)-septate to submuriform, ellipsoid, 24-32 x 11-15 µm, halonate; Pycnidia: frequent, black, almost globose, on the prothallus or immersed in the areoles; conidia: hyaline, filiform, 6-12 x 0.4-0.6 µm; Spot tests: medulla K+ yellow, C-, KC-, P+ yellow; Secondary metabolites: stictic acid according to Runemark (1956) but not confirmed by Thomson (1997).; Substrate and ecology: on siliceous rocks and walls, in low, moist and cool places; World distribution: Greenland, North and South America, and widespread in Europe; Sonoran distribution: Arizona.