Thallus: 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 Ám thick laterally, 20-50 Ám 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 Ám wide) apically, not pigmented; subhymenium: hyaline, 15-20 Ám 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 Ám 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.