Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2002. Lichen Flora of the Greater Sonoran Desert Region. Vol 1.

Thallus: to c. 3 cm across, to 2 mm thick in center, verrucose-squamulose, strongly polyphyllous; subunits scattered to contiguous or crowded, 0.3-1.3 mm across, convex, becoming ± sinuous and plicate lobes: similar to central subunits or somewhat more flattened and becoming slightly elongated and divided, c. 1-1.5 mm long, ultimate segments c. 0.5 mm wide upper surface: often somewhat powdery-roughened but not distinctly pruinose, pale yellowish green to somewhat whitish, edges concolorous lower surface: pale to dark brownish; umbilicus: indistinct, consisting of the narrowed base of the squamules; rhizinose strands: sometimes present Apothecia: common, laminal, 0.7-1.5 (-3) mm diam., usually soon sessile and constricted at base; disc: plane or slightly concave, usually ± strongly orange, pruinose, and appearing light to moderate orange; in occasional specimens (especially from areas north of the Sonoran region) younger discs and ones exposed to strong light becoming bluish black and often epruinose; thalline margin: concolorous with thallus, 0.1-0.2 mm wide, entire to flexuous, often soon crenulate towards inside, somewhat raised and slightly inflexed especially when young, usually persistent; hymenium: pale yellowish or orangish, not inspersed, but the uppermost part usually covered with granules; paraphyses tips: hyaline and scarcely thickened, or occasionally becoming at least partly greenish-blue and ± capitate, to 3-5 µm ascospores: (in material with placodiolic acid) ellipsoid to narrowly ellipsoid or slightly ovoid, (7-) 9-10 (-12) x (3-) 4 (-5) µm Pycnidia: occasional conidia: 15-25 µm long Spot tests: upper cortex: K- or + yellowish, C-. KC+ yellow, P-, UV-; medulla: K- or (rarely, in non-Sonoran material, K+ yellow or red), C- or rarely C+ red, KC-, P- or occasionally P+ yellow, UV- Secondary metabolites: upper cortex: in our region with placodiolic acid (major), usnic acid (minor); medulla: without lichen substances, or occasionally with psoromic or rarely lecanoric acid chemosyndromes or unidentified substances; the norstictic acid chemosyndrome occurs rarely (in Europe). Substrate and ecology: on basalt, rhyolite, granite, and sandstone (including calciferous types); on exposed, dry, steep surfaces (in northern areas often south-facing), in pinyon-juniper and oak woodlands, and in pine forests, World distribution: chemotypes containing placodiolic acid (± other substances) occur in warm-temperate to boreal-arctic areas of Asia, Europe, and western North America; psoromic or rarely lecanoric acid occurs in some specimens (including ones from Arizona, but also from some northern localities); the report of "Lecanora subdiscrepans" from South America is dubious Sonoran distribution: Arizona, Baja California Sur and Sonora at 1200-2900 m; southern California (San Bernardino Co.) at 1830 m. Notes: Material from the Sonoran region is similar to that from other areas in western North America, and from Eurasia (and differs from that in eastern North America), in usually containing placodiolic rather than pseudoplacodioic acid, having relatively long and narrow ascospores, and including occasional specimens (e.g., one from Gila Co., Arizona) with discs that are at least partly bluish or bluish black as in R. melanophthalma. As treated here, R. subdiscrepans can be distinguished from both R. melanopthalma and R. chrysoleuca (with which it sometimes grows side by side) especially by the numerous and crowded, distinctly convex to plicate and at most vaguely umbilicate thallus subunits, with lower surface completely lacking greenish or bluish black tinges, and from Lecanora opiniconensis and related taxa (with which it is frequently associated in North America and Asia) especially by having pruinose discs and a more matt and grayish thallus lacking yellowish to orange lobe tips.