Thallus: crustose, leprose or dispersed-verrucose, ecorticate; prothallus: not visible surface: whitish to greenish gray, rough, dull, epruinose, with an indistinct margin, esorediate Apothecia: sessile to slightly constricted at the base, 0.5-1.2 mm in diam. disc: pale to dark red-brown, whitish gray to bluish gray pruinose margin: whitish gray, paler than the thallus, thin to thick, entire, ±verruculose, without a parthecial crown amphithecium: present, with numerous algal cells, with large crystals insoluble in K, corticate; cortex: hyaline, indistinct, inspersed with small crystals, c. 10 µm thick laterally and 10-25 µm thick basally parathecium: hyaline, containing small crystals soluble in K, 15 µm thick epihymenium: dark red-brown, with pigment dissolving in K, with small crystals dissolving in K, 10-15 µm, thick hymenium: hyaline, clear; paraphyses: sparingly branched and thickened apically; subhymenium: hyaline, 15-20 µm thick; hypothecium: hyaline, without oil droplets asci: clavate, 8-spored ascospores: hyaline, simple, ellipsoidal, 12.5-17.5 x 6.5-8.5 µm Pycnidia: not seen Spot test: thallus and apothecial margin K+ yellow, C-, KC-, P+ yellow Secondary metabolites: atranorin (minor), chloroatranorin (major), zeorin (major), and traces of unidentified terpenes. Substrate and ecology: on the bark of deciduous trees or conifers, rarely on rocks World distribution: subcosmopolitan in semi-arid areas, known from North and South America and Australia Sonoran distribution: Baja California, Baja California Sur, and Chihuahua. Notes: Lecanora casuarinophila is easily recognized by its leprose thallus, the pruinose apothecial disc, the granulose epihymenium, and the presence of atranorin and zeorin. The species may be confused with L. caesiorubella, but this species is readily distinguished by the presence of depsidones, absence of an amphithecial cortex, and a more heavily pruinose apothecial disc. Another similar species is L. flavidomarginata, that also has pruinose disc, but differs in having a verrucose, entire thallus and containing usnic acid with chloroatranorin as major constituent. These are the first records for the species from North America.