Thallus: crustose, verrucose to squamulose, 2-4(-5) cm across, 3-5 mm thick; prothallus: when visible usually white or rarely pale blue or green, fimbriate or occasionally zonate areoles: narrowed at the base, highly convex-bullate, becoming plicate, foveolate, or subcerebriform, contiguous to very crowded, 1-3 mm wide upper surface: olivaceous green, to partly brown, white, pale gray, pale yellow, or pale pink, in herbarium becoming strong yellowish brown to brownish orange, sorediate soredia: finely granular, pale yellowish green (fading to white, in herbarium) becoming light orange or light pink, in superficial, elongated to +round, concave soralia (becoming convex and capitate) scattered on edges or undersides of areoles initially but expanding to cover large parts of the upper surface upper cortex: often with dead algal cells, light brown, inspersed with fine pale yellow crystals (partly soluble in K), 20-30 µm thick; hyphae: anticlinal to unoriented, gelatinized, medulla: loose, the central part becoming almost hollow; hyphae: mostly elongated, unoriented, interwoven, with rather thick walls and thin lumina, 3-5 µm wide on attenuated parts, +incrusted with coarse crystals (insoluble in K) and water-repellent, forming coarse and irregular air-filled lacunae; algal layer: up to 70-85 µm thick, continuous lower cortex: developed mainly towards the edges, similar to upper cortex lower surface: yellowish gray; rhizinose strands: mostly not distinctly differentiated from the prothallus Apothecia: rare or occasionally numerous, broadly sessile, 1-1.5 mm in diam., lecanorine to biatorine disc: grayish violet to dark violet, brownish or bluish black, usually plane then soon convex, usually somewhat pruinose and appearing dark bluish gray, sometimes epruinose and nitid margin: +concolorous with thallus, c. 0.1 mm wide, often irregularly sinuous, at first slightly raised, with a bluish black parathecial ring amphithecium: present, either without an algal layer or with an interrrupted one (c. 100 µm thick) marginally and below the hypothecium, medulla with distinctly anticlinal, branched, thick-walled hyphae c. 2 µm wide, with numerous air-filled rounded lacunae, corticate; cortex: in upper part 20 µm thick laterally, 30-100 µm thick on lower side, strongly gelatinized and conglutinate, inspersed with non-crystalline granules parathecium: hyaline, strongly gelatinized, strongly swollen, towards the upper side mostly widened and divided into compartments, with hyphae in areas towards the margin +parallel and with somewhat elongated cells epihymenium: olive green, or dirty violet-brown at surface, with greenish blue streaks into hymenium, 10 µm thick, not inspersed or with superficial granules when discs pruinose hymenium: hyaline, very strongly conglutinate, 50-70 µm tall; paraphyses: very crowded, mostly simple, the tips olive (K+ green, N+ red), not or only weakly thickened, conspicuously filled with oil droplets; hypothecium: hyphae unoriented, c. 2 µm in diam. with short, narrow lumina asci: often not developed, clavate, c. 50 x 12 µm, apparently typical Lecanora-type, up to 8-spored ascospores: hyaline, simple, subglobose to mostly short-ellipsoid, (6.5-)9-10(-13) x 5-6(-7) µm Pycnidia: uncommon; conidiophores: +type III of Vobis (1980) conidia: hyaline, filiform, often curved, 15-20 µm long Spot tests: upper cortex K+ yellow, C-, KC+ red, P-; soralia and underside of squamules: C+ pinkish red to scarlet, KC+ red, P+ yellow; prothallus: K+ yellow, C+ pinkish red to scarlet, KC+ red, P+ yellow Secondary metabolites: atranorin, alectorialic acid, thamnolic acid or unknown substances. Substrate and ecology: on hard siliceous rocks in alpine areas World distribution: Europe, western North America and New Zealand Sonoran distribution: alpine areas in Arizona. Notes: This very distinctive species is similar to L. pringlei ssp. brandegei (see discussion under that taxon), but is easily recognized by the pinkish soralia (reflecting its alectorialic acid content), that appear to be unique among crustose lichens in the Sonoran region. The apothecia of L. cavicola tend to be more sessile and more clearly lecanorine than in L. pringlei ssp. brandegei. A non-sorediate taxon that is otherwise superficially similar to L. cavicola in thallus color and morphology also occurs in the San Francisco Peaks, but has more solid areoles and distinctly lecideine apothecia; it may belong to Lecidea s. str., but needs further study.