Thallus: areolate to subsquamulose, overall up to 2 cm wide areoles: irregular, bullate, lobed or not, up to 3 mm in diam., 0.4-1.2 mm thick, discrete or contiguous in small groups, formed by division from central elevated areoles; rim:±down-turned upper surface: brown to brown-red, dull or somewhat glossy, convex, smooth to rugulose, fissured or not, epruinose upper cortex: paraplectenchymatous, 40-60 µm thick, hyphae with distinct or obscure cellular lumina in water; syncortex: 10-25 µm thick; eucortex: upper layer pigmented brown and 10-13 µm thick, lower layer hyaline to smoky yellow and 20-25 µm thick algal layer: upper surface even, thin, lower layer tending to be uneven medulla: white, prosoplectenchymatous lower surface: beneath extended rim, ecorticate, white or mineral-stained attachment: broad, eventually becoming elevated through thickening of medulla (gomphate), without a stipe Apothecia: 1-5 or more per areole, round, becoming conspicuously elevated, 0.2-0.5 mm wide (but 1-2 mm wide in European specimens) disc: same color as thallus or more red; surface distinctively rough, scabrid parathecium: expanded up to a width up to 100 µm, becoming elevated, forming a crown around the apothecium epihymenium: yellowish brown, with an uneven surface, 10-15 µm thick hymenium: hyaline to pale yellow, 110-170 µm tall; paraphyses: 1.5-2 µm wide at base, apices slightly expanded, sometimes with dark pigment hoods, conglutinated subhymenium: smoky brown, 30-50 µm thick; hypothecium: 12-17 µm thick, prosoplectenchymatous asci: clavate, 75-90 x 15-20 µm, 100+-spored ascospores: hyaline, simple, ellipsoid, 4-5 x 1.7-2 µm Pycnidia: not observed Spot tests: UV-, all spot tests negative Secondary metabolites: none detected. Substrate and ecology: on acidic rocks, including schist, reported from soil in Scandinavia World distribution: Fennoscandia, North America (Canada, New York), South America Sonoran distribution: Arizona (South Mountain in Phoenix) and southern California. Notes: Acarospora scabrida is easily distinguished by its bullate areoles with elevated apothecia, that have well-developed parathecial crowns. There is no other brown species in the Sonoran region that looks similar. It is apparently another example of a temperate lichen species pushed south during the glacial period and now remaining as a relic in southwestern North America. Sonoran specimens best matched specimens from Finland. While Sonoran specimens match specimens from Finland, the lectotype is more subsquamulose in form, probably from increased nitrogen in environment, and is on soil.