Thallus: crustose, continuous or verrucose areolate; prothallus: not visible areoles: flat or verrucose or verruculose, thin or thick, opaque, ecorticate surface: yellowish white to yellowish gray, smooth or rough, epruinose, with a distinct margin, esorediate Apothecia: sessile or adnate, often crowded, 0.5-1.3 mm in diam., lecanorine disc: orange-brown to yellowish brown, plane; slightly to heavily whitish gray or pale yellow pruinose margin: concolorous with thallus, thick, persistent, prominent, flexuose, smooth, verrucose or verruculose, with or without a parathecial ring amphithecium: present, with numerous algal cells, with large crystals insoluble in K, corticate; cortex: hyaline, distinct, basally slightly thickened, gelatinous or interspersed, 15-30 µm thick laterally, 15-35 µm thick basally parathecium: hyaline, containing crystals soluble in K epihymenium: without pigmentation, with crystals dissolving in K hymenium: hyaline, clear; paraphyses: thickened (up to 3.5 µm wide) apically, not pigmented; subhymenium: hyaline, 15-20 µm thick; hypothecium: hyaline, without oil droplets asci: clavate, 8-spored ascospores: hyaline, simple, ellipsoid or broadly ellipsoid, (9.5-)11.5-13(-13.5) x (5.5-)6-7(-8.5) µm; wall: less than 1 µm thick Pycnidia: not seen Spot tests: K+ yellow, C-, KC-, P- or P+ pale yellow Secondary metabolites: atranorin (major), chloroatranorin (minor), gangaleoidin (major), and norgangaleoidin (minor). Substrate and ecology: on tree bark of Quercus World distribution: endemic to North America, known from central Mexico and the southern Rocky Moun Sonoran distribution: Arizona, southern California, Baja California Sur and Chihuahua. Notes: Lecanora viriduloflava is characterized by the pruinose apothecial disc. It may be confused with other species that have heavily pruinose disc, such as L. albella or L. carpinea. The former lacks an amphithecial cortex and contains depsidones, while the latter is easily distinguished by the C+ orange reaction of the apothecial disc due to the presence of the sordidone chemosyndrome. L. chlarotera is also similar, but lacks a pruina.