Thallus: areolate, sometimes rimose at the edge, (2-)4-8(-12) cm in diam., (0.1-)0.2-0.6(-1.0) mm thick areoles: angular, sometimes round or irregular, flat to slightly concave or convex, (0.2-)0.4-1.0(-2.0) mm in diam., contiguous, separated by distinct cracks prothallus: often absent, when present forming a narrow, dark zone at the thallus edge, sometimes fimbriate, black to olive-black or blue-black, 0.1-0.5(-1.5) mm wide surface: brown with an ±olive tinge to sometimes almost olive, often mottled with gray to white areas; brown areas ±shiny, gray areas dull upper cortex: (15-)20-40(-50) µm thick, with ±crystals, uppermost part ±brown, 7-12(-15) µm thick, with cells (4-)5-7(-9) µm in diam.; cortex covered with an epinecral layer 5-15(-25) µm thick photobiont: chlorococcoid, cells ±round, 5-15(-21) µm in diam. Apothecia: aspicilioid, usually numerous, (0.1-)0.2-0.8(-1.1) mm in diam., 1-2(-6) per areole, round to angular or sometimes elongated; rarely elevated disc: black, usually concave, sometimes plane, rarely convex, without pruina or with ±white pruina thalline margin: usually flat to slightly elevated, rarely prominent, often with a white to gray rim or concolorous with thallus, rarely darker exciple: (20-)30-70(-100) µm wide, I- or partly I+ blue medially, rarely entirely I+ blue; uppermost cells brown to olive-brown, ±globose, (4-)5-6(-7) µm in diam. epihymenium: green to olive or olive-brown, rarely brown, without or with a few crystals, rarely with numerous crystals, N+ green to blue-green, K+ brown hymenium: hyaline, I+ persistently blue, (120-)140-180(-200) µm tall paraphyses: moniliform, with (2-)3-6(-10) upper cells ±globose, (3-)3.5-5(-6) µm wide, in lower part 1.5-2(-2.5) µm wide, slightly branched and anastomosing subhymenium and hypothecium: pale, I+ persistently blue, together (30-)40-70(-85) µm thick asci: clavate, (60-)80-120(-130) x (18-)20-33(-38) µm, 8-spored ascospores: hyaline, simple, ellipsoid, (15-)19-26(-28) x (9-)10-16(-18) µm Pycnidia: rare to rather common, 1-2(-5) per areole, immersed, often with a white rim, rarely aggregated, (90-)130-250(-400) µm in diam., with a black, punctiform to sometimes elongated ostiole, (50-)70-150(-200) µm in diam. conidia: filiform, straight or slightly curved, (10-)13-19(-23) x (0.6-)0.8-1(-1.2) µm Spot tests: cortex and medulla I-, K+ red, P+ orange, C- Secondary metabolites: norstictic acid, usually also with trace of connorstictic acid. Substrate and ecology: on siliceous or volcanic rock; rarely on calciferous rock World and Sonoran distribution: common in Arizona and northern Mexico (Chihuahua), rare in southern California and Sonora, at 530-3360 m. Notes: Aspicilia olivaceobrunnea seems to be a common species in Arizona and northern Mexico (Chihuahua). It is characterized by its thallus color, which is brown with a ±olive tinge to sometimes almost olive, often mottled with gray to white areas. Furthermore, the apothecia usually have a gray to white thalline rim, the hymenium is tall, the paraphyses are moniliform, the spores are large (usually over 20 µm), the conidia are filiform of medium length, and it contains norstictic acid. Many specimens of A. olivaceobrunnea have previously been determined to Aspicilia cinerea, which, however, differs by its gray to white thallus color, its usually larger and often confluent apothecia, its shorter hymenium, and its smaller spores (usually less than 20 µm long). Several other norstictic containing species occur in the Sonoran area, but mainly in California. Aspicilia brucei has smaller apothecia, non-moniliform to submoniliform paraphyses, small spores and short conidia. Aspicilia cuprea differs in thallus color, and has much longer conidia than A.olivaceobrunnea, while Aspicilia knudsenii has submoniliform paraphyses, usually shorter conidia and by having stictic acid as a major substance and norstictic acid usually only in minor amounts. Aspicilia pacifica and Aspicilia santamonicae both have shorter conidia than A. olivaceobrunnea. According to DNA studies, A. olivaceobrunnea is related to Aspicilia americana, which lacks norstictic acid.