Thallus: crustose, continuous or verrucose areolate; prothallus: not visible or white areoles: flat or verrucose, thin, opaque, ecorticate surface: grayish white to yellowish gray or greenish white, smooth, epruinose, with a distinct margin, esorediate Apothecia: constricted at base or sessile, lecanorine, 0.4-2.5 mm in diam. disc: red-brown or dark brown, plane; shiny and epruinose margin: concolorous with thallus or lighter than thallus, thick, persistent, even, not flexuose, smooth, crenulate or verruculose, without a parathecial ring amphithecium: present, with numerous algal cells, with large crystals, insoluble in K, corticate; cortex: hyaline, distinct, basally thickened, gelatinous, interspersed, 15-30 µm thick laterally, 25-45 µm thick basally parathecium: hyaline, lacking crystals epihymenium: red-brown, with pigment insoluble in K, lacking crystals hymenium: hyaline, clear; paraphyses: slightly thickened (up to 3 µm wide) apically, brownish pigmented at tips; subhymenium: hyaline, 15-20 µm thick; hypothecium: hyaline, without oil droplets asci: clavate, 8-spored ascospores: hyaline, simple, broadly ellipsoid, (9.5-)11-16(-18) x (5.5-)6.5-8.5(-10) µm; wall: c. 1 µm thick Pycnidia: not seen Spot tests: K+ yellow, C-, KC-, P+ pale yellow Secondary metabolites: atranorin (major), chloroatranorin (minor), roccellic acid (major). Substrate and ecology: on bark of deciduous trees and conifers World distribution: Holarctic, recorded from Africa, Europe, and North America Sonoran distribution: southern California and Sonora. Notes: Lecanora subrugosa is characterized by the red-brown apothecial disc, the egranulose epihymenium and the lack of phenolic substances in addition to the atranorin chemosyndrome. Similar species include L. circumborealis and L. hybocarpa and L. pulicaris. All these three species differ, however, in having a granulose epihymenium. L. argentata is also similar, but differs in containing the gangaleoidin chemsyndrome. The specimens are only tentatively referred to th name L. subrugosa following Brodo (1984). The type of L. subrugosa and European collection differ in containing the gangaleoidin chemosyndrome and it has been suggsted that L. subrugosa is a synonym of L. argentata. We agree, however, with Brodo (1984) that the North American popuation is distinct. The correct classification of this difficult aggregate awaits further studies.