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DescriptionThallus: crustose, rimose to verrucose or verruculoseareolate; prothallus: not visible or blackish brown; areoles: flat to verrucose, thin to thick, opaque, ecorticate; surface: yellowish white to yellowish gray or greenish white, smooth, epruinose, with an indistinct margin, esorediate; Apothecia: constricted at base, 0.4-1.4 mm in diam., lecanorine; disc: orange-brown or yellowish brown to brown, plane or convex, epruinose or slightly whitish gray pruinose; margin: concolorous with thallus but lighter than disc, thin or thick, persistent, even or prominent, not flexuose, smooth, verrucose or verruculose, with a parathecial ring,; amphithecium: present, with numerous algal cells, with large and small crystals, large crystals insoluble in K, corticate; cortex: hyaline, distinct, basally slightly thickened, interspersed with numerous small crystals, 15-40 µm thick laterally, 20-50 µm thick basally; parathecium: hyaline, containing small crystals insoluble in K; epihymenium: yellowish brown to orange-brown, with pigment dissolving in K, with crystals dissolving in K; hymenium: hyaline, clear; paraphyses: sparingly branched and slightly thickened (up to 3 µm wide) apically, not pigmented; subhymenium: hyaline, 15-20 µm thick; hypothecium: hyaline to yellow, darker yellow in K, without oil droplets; asci: clavate, 8-spored; ascospores: hyaline, simple, broadly ellipsoid, 9.5-13.5 x 6.5-9.5 µm; Pycnidia: not observed; Spot tests: K+ yellow, C+ orange, KC+ orange, P+ pale yellow; Secondary metabolites: containing arthothelin (major), atranorin (major), chloroatranorin (minor), isoarthothelin (major), and zeorin (major).; Substrate and ecology: on bark of trees; World distribution: endemic to southwestern North America; Sonoran distribution: Chihuahua, Sinaloa, and Sonora.; Notes: Lecanora pseudachroa is characterized by brownish apothecial discs, the presence of xanthones, and broadly ellipsoid ascospores. L. achroa differs in chemistry and having lighter apothecial discs, while L. arthothelinella has a similar chemistry, but lacks zeorin. Additionally this species differs in having lighter apothecial discs and narrower ascospores.