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DescriptionThallus: 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).