Thallus: minutely squamulose, 2-3 mm in diam., crust-like, swollen, usally occurring on a thin, blue-black hypothallus squamules: often irregularly rounded and incised, margin often upturned upper surface: blue gray to olive-brown, often white-felted to tomentose marginally (in the herbaria often with crystals of terpenoids) soredia: granular, lead-gray, in soralia that are formed on the upturned margins upper cortex: paraplectenchymatous with irregularly thickened cell walls, 30-40 µm thick Apothecia: rare and not yet known in American collections, up to 2 mm diam., with distinct thalline, sorediate margin; exciple: subparaplectenchymatous, 20-30 µm thick; hymenium: I+ blue-green and rapidly turning red-brown, up to 100 µm high asci: clavate to subcylindrical, with apical amyloid tubes, 8-spored ascospores: ellipsoid, with a thick epispore and broadly attenuated apices, 17-23 x 8-9 µm (with epispore; otherwise 14-16 x 7-8 µm) Spot tests: all negative Secondary metabolites: terpenoids and aliphatic acids (see Jørgensen 1991). Substrate and ecology: on coarse, acidic bark (Alnus and Quercus spp.), often on the dry side of the trees World distribution: mainly in the regions with a Mediterranean or oceanic climate in Europe, North and South America, but also extending as far south as Tierra del Fuego, and as far north as the Lappmark region in Scandinavia (where it is saxicolous) Sonoran distribution: rare, only collected in forested valleys of Arizona (Pinaleño Mts.) at about 2000 m. Notes: It is an easily recognized species due to its unique color and is not likely to be confused with any other species known from the region, except for stunted specimens of Pannaria conoplea which are paler gray-blue, and never olive-brown, and reacts P+ orange (pannarin). Further north (Oregon and Washington) there is a similar species, Fuscopannaria leprosa P. M. Jørg. & Tønsberg, that totally dissolves into soredia. The latter species appears to require cooler, damper habitats than those available in the Sonoran region and is not likely to occur here. The terricolous Fuscopannaria cyanolepra (Tuck.) P. M. Jørg., on the other hand, may grow on river banks in the Sonoran region. In addition to its different ecology, F. cyanolepra is recognizable by its very thick, crust-forming squamules that are mostly dissolved into soredia, because it is corticate only in central parts.