Thallus: placodioid, strongly adherent to substrate, 1-3 cm in diam., composed of scattered to contiguous or weakly imbricate areoles; prothallus: absent, or forming inconspicuous black edges and thin black layer visible beyond the lobe tips; areoles: plane to slightly convex, 0.5-1.5 mm across; margins: not thickened or raised, crenate; lobes: somewhat enlarged, isodiametric to moderately elongated, 1-3 mm long, 1-1.5 mm wide, plane, discrete or contiguous, coarsely crenate at the tips; surface: pale yellow to grayish or greenish yellow, dull to slightly shiny, often slightly rimose, epruinose or occasionally slightly patchily pruinose in places, esorediate; cortex: often containing empty algal cells, the lower part connected to the medulla by narrow, somewhat cone-like hyphal bundles, mostly 50-75 µm thick; medulla: solid, often composed of anticlinal hyphae throughout; algal layer: irregular but continuous; Apothecia: common, mostly restricted to the central parts of the thallus, immersed when young but soon adnate to broadly sessile, 1(-4) per areole, up to 1.5 mm in diam., sometimes crowded, often irregular in outline; disc: pale orangish yellow, pale yellow, yellowish gray, light olive-gray, light grayish yellow-brown or light yellowish brown, sometimes darkening to light brown towards the center, plane to somewhat convex, epruinose; margin: concolorous with or slightly paler than the thallus and little differentiated from it, even with the disc or slightly raised, persistent or finally crowded, without a parathecial ring; amphithecium: present, anatomically similar to L. laatokkaensis; parathecium: hyaline, composed of conglutinated, radiating hyphae 4-5 µm wide and with narrow (0.5-1 µm wide) lumina that are 5-7 µm long, becoming confluent with the hypothecium, 75-100 µm thick at the top; epihymenium: orangish brown, inspersed with fine granules (soluble in K), 10-15 µm thick; hymenium: hyaline, 60-70 µm tall; paraphyses: hyaline, tips somewhat enlarged, 2.5-3 µm wide; hypothecium: with hyphae 5-7 µm wide and lumina 5-15 µm long, unoriented, or up to 200 µm thick between algal clumps and then hyphae becoming anticlinal to the disc; 100-125 µm thick; asci: clavate, 8spored; ascospores: hyaline, simple, ellipsoid to narrowly ellipsoid or ovoid-ellipsoid, (10-)12-13(-15) x 5-6(-7) µm; Pycnidia: not found; Spot tests: thallus: K-, C-, KC-, P-; cortex KC+ yellow; medulla KC-, I2KI-; Secondary metabolites: cortex with usnic acid; medulla containing zeorin and other triterpenes (same ones as in L. laatokkaensis), and sometimes an unknown substance (probably a contaminant).; Substrate and ecology: on hard siliceous rocks, 2150-3475 m; World distribution: SW North America (Arizona, Colorado); Sonoran distribution: central Arizona at 2150 m.; Notes: Lecanora mazatzalensis is rather similar to L. laatokkaensis, but differs in that its areoles are a paler, more grayish shade of yellow, with at most a very thin black edge and hypothallus, and the apothecial disc are distinctly paler. The apothecia are also more often solitary and soon adnate to sessile. These differences (especially in color of the upper surface), are rather subtle, but they are enough to consistently distinguish the two species when they grow side by side, as in the Mt. Baldy Wilderness Area in Arizona (even though the material of L. laatokkaensis there has a less distinct hypothallus and more adnate apothecia than usual). Lecanora mazatzalensis could also possibly be confused with members of the L. polytropa complex, with which it occurs, but is easily distinguished by the structure of the apothecial margin. For comparison with L. geiserae, see under that species