Thallus: crustose, areolate; prothallus: usually not visible, rarely distinct and black areoles: flat to subbullate, sometimes squamulose, often irregular, up to 1.2 mm in diam. surface: pale ochre to greenish ochre to reddish brown, rarely gray, smooth to faintly glossy or rough, esorediate cortex: 10-25 µm thick; C+ red medulla: white, I-, C- Apothecia: black, with a slightly constricted base, occurring between and often not overtopping the areoles, up to 1.6 mm in diam. disc: black, flat to moderately convex, sometimes pruinose with a rough surface margin: black, usually small, sometimes paler towards the thallus, persistent or disappearing in larger apothecia, dull to shiny exciple: blackish brown peripherally, very pale within, densely inspersed by crystalline masses, C+ red, 40-80 µm wide epihymenium: olive green to brown (cinereorufagreen in small amounts), 10-20 µm thick hymenium: hyaline, 50-95 µm tall, I+ orange in fresh material, I+ blue in herbarium specimens; paraphyses: simple, but relatively often branched and anastomosing subhymenium: unpigmented, 17-45 µm thick hypothecium: dark brown to almost black, 80-250 µm thick asci: clavate, 60-85 x 1418 µm, 8-spored ascospores: hyaline, simple, ellipsoid, (8-)10.2-15.5(-21) x (4.5-)5.1-7(-8) µm, length-width-index: 1.8-2.8 Pycnidia: immersed conidia: cylindrical, (6-)7-14(-18) x 1-1.3 µm [studied in 18 specimens]; thick-walled, with globular thalloconidia 6-8 µm in diam. rarely produced at the margins of squamulous areoles Spot tests: cortex and medulla K-, C+ red, KC+ red, P- Secondary metabolites: chemical race A: gyrophoric acid syndrome (very common); chemical race B: gyrophoric acid syndrome + 2'-O-methylperlatolic acid (rare); chemical race C: gyrophoric acid syndrome + schizopeltic acid (rare). Substrate and ecology: in open habitats on granites, schist and other acid rock types, from lowlands to the montane (rarely to the alpine) belt and preferably on highly insulated, frequently dry rock surfaces World distribution: bipolar and extending into the tropics in alpine areas Sonoran distribution: southern California, Baja California and Chihuahua. Notes: Lecidea fuscoatra is a very widespread and polymorphic lichen, characterized by its I- reaction of the medulla, its dark hypothecium, its relatively large ascospores and its C+ red reaction (caused by gyrophoric acid). Linné named it Lichen fusco-ater (Latin: fuscus = dark brown and ater = black) because of its dark brown thallus and its black "tubercles" (= apothecia).