Thallus: crustose, usually well developed, effuse, composed of convex areoles; occasionally immersed and indistinct surface: white to pale gray (green in shade forms), smooth but not corticate Apothecia: sessile, 0.1-0.5 mm in diam. disc: dark gray to black (pale gray to whitish in shade forms), strongly convex, epruinose proper exciple: usually excluded, even in young apothecia epihymenium: dull green, K+ violet hymenium: 25-40 µm tall; paraphyses: numerous, branched and anastomosing, 1-1.5 µm wide, not capitate; hypothecium: hyaline, 60-110 µm thick asci: clavate, 28-36 x 9-12 µm, 8-spored ascospores: hyaline, 1-septate, ellipsoid, often ±curved, 9-16 x 2.5-3.5 µm, Pycnidia: usually present, immersed to emergent, gray to black, 30-150 µm wide conidia: composed of three types: i) macroconidia, curved, (1-)3 septate, 12-24 x 1 µm; ii) mesoconidia, simple, 2.5-4.5 x 1-2 µm; iii) microconidia, simple, 5-7.5 x 0.5-1 µm Spot tests: K-, C+ red (in section), KC+ red, P- Secondary metabolite: gyrophoric acid. Substrate and ecology: usually on wood, occasionally on rock World distribution: widespread in Europe and western North America, Newfoundland, and Australia Sonoran distribution: several collections from southern California (Los Angeles (on rock), Riverside, San Diego, and Santa Barbara Cos.), one from Arizona (Santa Cruz Co.). Notes: Micarea denigrata is very similar to M. nitschkeana, which has 3-septate ascospores and usually occurs on twigs, and M. misella, which has simple ascospores and an endoxylic thallus. Shade forms with a green thallus and pale apothecia resemble M. prasina aggr., but can be separated from that species by the C+ red reaction of the thallus (in section) and apothecia sections. The microconidia occur in the smallest pycnidia.