Thallus: placodioid, bullate-areolate to squamulose-areolate, 1-3 cm across, 2-3 mm thick, tightly adnate or or becoming detached from substrate, thin to thick; prothallus: absent, or vestigial as thin black edges around the lobes areoles: often rugose, up to 1 mm wide lobes: weakly radiating, often imbricate, tightly to +loosely attached, 1.5-2 mm long, 0.3-0.6 mm wide, weakly to strongly convex, incurved at tips, subentire to richly and finely divided, the branching irregular to flabellate; ultimate segments: 0.2-0.7 mm wide upper surface: pale to light greenish yellow to light or dark yellow or grayish yellow, usually with brownish or orangish tint (at least in herbarium), smooth to +rimose and foveolate (with numerous apothecial primordia), dull to almost shiny, epruinose to densely but spottily pruinose at least towards the center, esorediate upper cortex: with strongly swollen hyphae and numerous dead algal cells, 30-40 µm thick medulla: with mostly anticlinal hyphae and uniformly, pale yellow, granular crystals (insoluble in K); algal layer: rather continuous lower cortex: absent or somewhat developed near tips or edges of lobes, thin and poorly differentiated Apothecia: few to many, restricted to thallus center, 1-several per areole, 1-2(-4) mm in diam. disc: uniformly light to medium orangish yellow to orange or pale brown, or (especially near margin or when young) strongly to dark yellowish to reddish brown, dull to almost shiny, concave to plane, often soon very convex, epruinose; margin: entire to flexuous or crenate towards outside, sometimes raised when young, 0.1(-0.2) mm wide, persistent or becoming excluded, without a parathecial ring amphithecium: with a well-developed, somewhat interrupted algal layer in the margin and extending below the hypothecium, with small grayish granules (insoluble in K) in the medulla, similarly corticate to the thallus parathecium: hyaline, 20-40 µm thick; with periclinal, strongly conglutinate, and elongated hyphae epihymenium: inspersed with fine granules (soluble in K), without hyaline layer on top, c. 20 µm thick hymenium: hyaline, c. 60 µm tall; paraphyses: hyaline, tips: 2-3 µm wide; subhymenium: pale brown, c. 40 µm thick, with oil droplets; hypothecium: 20-40 µm thick, the hyphae randomly oriented to periclinal asci: clavate, 8-spored ascospores: hyaline, simple, ellipsoid, often not well-developed, 7-11 x 4-7 µm Pycnidia: immersed; ostioles: pale to dark yellowish brown; conidiophores: type III of Vobis (1980) conidia: 15-25 µm long Spot tests: thallus K-, C-, KC-, P-; cortex KC+ yellow; medulla KC- Secondary metabolites: cortex with usnic and placodiolic acids; medulla with or without unidentified terpenoids and occasional unknowns. Substrate and ecology: on sandstone, 1000-2380 m World distribution: semi-arid areas of central Asia and western North America (primarily in the Great Basin and the foothills of the Rocky Mountains) Sonoran distribution: Arizona at 1000-2380 m and southern California. Notes: Lecanora phaedrophthalma is quite variable in morphology and appearance, and to some extent in chemistry, but can be distinguished from L. muralis by having placodiolic acid as the major substance, and from both that species and L. opiniconensis especially by the tendency of the discs to be darker and more deeply pigmented when young and next to the margin. The ecology of this species in North America is rather different than in Asia, where it occurs mostly on steep to overhanging surfaces and mostly at 2500-5000 m elevation.