Thallus: areolate, (1-)4-10(-15) cm in diam., (0.2-)0.3-0.6(-1) mm thick areoles: angular, sometimes irregular or aggregated, flat to slightly convex or uneven, (0.2-)0.4-1.1(-2) mm in diam., contiguous, rarely dispersed, separated by distinct cracks prothallus: often present at the thallus edge as a thin, continuous zone or fimbriate, black to brown-black, olive-black or blue-black, rarely with a white outer part, 0.3-0.6(-2) mm wide surface: gray to white-gray, sometimes partly brown-gray to olive-gray or light brown, dull to slightly shiny upper cortex: 20-40 µm thick, uppermost part ±brown, 5-10(-15) µm thick, with cells 5-6(-8) µm in diam.; cortex covered with an epinecral layer 3-12(-15) µm thick photobiont: chlorococcoid, cells ±round, 5-17(-22) µm in diam. Apothecia: aspicilioid, rare to rather common, (0.1-)0.3-0.9(-1.5) mm in diam., 1-2(-5) per areole, round to sometimes angular; fertile areoles often elevated disc: black, usually concave, sometimes plane, rarely convex, without pruina or rarely with a thin ±white pruina thalline margin: usually flat to slightly elevated, rarely prominent, often brown to olive-brown or brown-gray in contrast to the gray thallus, sometimes also with a thin white to gray rim near the exciple, or rarely concolorous with thallus exciple: 40-60(-70) µm wide, I- or partly I+ blue medially; uppermost cells brown, ±globose, 5-6(-7) µm in diam. epihymenium: green to olive or olive-brown, without or with a few crystals, N+ green to blue-green, K+ brown hymenium: hyaline, I+ persistently blue, 140-200(-260) µm tall paraphyses: moniliform, rarely submoniliform, with (2-)3-5(-8) upper cells ±globose, (3-)4-5(-6) µm wide, in lower part 1.5-2 µm wide, slightly branched and anastomosing subhymenium and hypothecium: pale, I+ persistently blue or partly turning yellow-green, or partly I-, together 40-70 µm thick asci: clavate, (70-)80-130 x 18-29 µm, 8-spored ascospores: hyaline, simple, ellipsoid, (16-)18-22(-25) x (9-)10-14(-16) µm Pycnidia: rare to rather common, 1(-4) per areole, immersed, rarely aggregated, 100-170 µm in diam., with a black, punctiform to sometimes elongated ostiole, 50-110 µm in diam. conidia: filiform, straight or slightly curved, (10-)13-20 x 0.8-1(-1.3) µm Spot tests: cortex and medulla I-, K-, P-, C- Secondary metabolites: none detected by TLC. Substrate and ecology: on ±shaded, siliceous rock; at the type locality in a gorge; at the other localities in forests Notes: Aspicilia fumosa is characterized by a gray to white-gray thallus, rather large apothecia, a thalline margin which often is darker than thallus, a tall hymenium, moniliform paraphyses, rather large spores, rather long conidia and the absence of secondary metabolites. The type specimen has been analyzed for DNA (ITS). Superficially A. fumosa resembles Aspicilia cinerea, which has shorter hymenium, smaller spores and contains norstictic acid. Aspicilia confusa, another gray and common species, has convex and ±dispersed areoles, smaller apothecia, a thalline margin concolorous with thallus and, according to the DNA analysis, is related to Aspicilia glaucopsina and A. phaea. Aspicilia cyanescens differs from A. fumosa by having a blue-gray thallus and a blue-green epihymenium, while A. americana has a different thallus color, and an apothecial thalline margin which is concolorous with or lighter than the thallus.