Life habit: lichenized Thallus: crustose, leprarioid, thin to thick, granular to effuse, becoming irregularly cracked with age granules: crowded, ellipsoid, corticate, 0.03-0.1 mm diam. upper surface: blue-gray to gray-blue-black, smooth to roughened upper cortex: poorly differentiated photobiont: primary one a species of Nostoc, secondary photobiont absent Apothecia: sessile or often sunken between thallus granules that may form a thalline exciple, up to 1 mm diam.; disc: becoming convex, pinkish brown to brown, with an irregular, granular thalline margin; proper exciple: paraplectenchymatous, composed of radiating hyphae, up to 100 µm thick; hymenium: I+ blue-green turning brown, up to 100 µm high; paraphyses: simple, straight, septate, conglutinate, externally brown; hypothecium: pale brown, of intricately interwoven hyphae asci: apically thickened, narrowly cylindrical, thin-walled; apex with an I+ blue apical dome, 8-spored ascospores: simple, colorless, ellipsoid, smooth, sometimes attenuated at one end with a single large oil droplet, 10-15 (-20) x 5-8 µm Pycnidia: unknown Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on sandy, well-drained soil, frequently as a short-lived pioneer species on disturbed soil World distribution: temperate regions of the Northern Hemisphere, rare Sonoran distribution: thus far only known in the Channel Islands on Santa Cruz in southern California. Notes: Potentially M. nebulosa may be confused with Fuscopannaria cyanolepra, a species that also occurs on soil. The latter species has a more striking plumbeous color and has corticated, olive-brown squamules centrally. A second subspecies, M. nebulosa ssp. frullaniae Maass is known from eastern Canada and southwestern Europe, but has not been found in the Sonoran region.