Thallus: placodioid, areolate to squamulose, +rosulate or lobate, tightly to loosely attached, thin to +thick; prothallus: absent areoles: plane to slightly convex, non-foveolate lobes: weakly differentiated, radiating or not, plane, 1-1.5 mm long, 0.5 mm wide upper surface: smooth, dull to slightly shiny or waxy, light to pale or grayish yellowish green, pale or light greenish yellow, pale gray or moderate yellow; epruinose or occasionally lightly pruinose at least on edges; lobe tips: usually becoming darker yellow or pale brown to orange, esorediate upper cortex: with dead algal cells, 20-40 µm thick, inspersed with yellowish granules soluble in K; hyphae: conglutinate, randomly oriented, 3-4 µm, lumina 3-7 x 0.5-1 µm; epinecral layer: 15-20 µm medulla: loose but solid; hyphae: 2.5-3.5 µm thick, without granules; algal layer: 25-30 µm thick, +continuous lower surface: dark grayish yellow-brown lower cortex: hyphae easily distinguishable hyphae, elongated Apothecia: adnate to sessile, soon constricted, 1-2 mm in diam. disc: +pale or moderate shades of grayish to orang-ish yellow, or yellowish brown, scarcely changed when wet, plane or convex, dull thalline margin: concolorous with thallus to pale green or more often distinctly orange (especially when young and next to disc), usually pruinose (at least in Sonoran material), slightly raised then level, 0.1-0.3 mm wide, flexuous, +crenate, persistent or finally excluded; parathecial ring: absent or thin and indistinct, deeper orange or brown colored amphithecium: present, with an interrupted algal layer (c. 50 µm thick) marginally and extending below the hypothecium, with a dense medulla with somewhat conglutinated hyphae, with clumps of fine granules (soluble in K, insoluble in N), or clumps of yellowish brown material towards the base, corticate; cortex: similar to that of thallus parathecium: pale yellow to orange, indistinctly delimited from hypothecium, with conglutinated, with randomly oriented hyphae c. 5 µm wide and with lumina 3-10 x 0.5 µm epihymenium: brownish yellow, heavily inspersed with fine granules (soluble in K, insoluble in N), c. 15 µm high hymenium: hyaline, c. 55 µm high; paraphyses: coherent, the tips hyaline, scarcely enlarged; subhymenium: pale brown to gray, 25-40 µm thick; hypothecium: hyaline, up to 120 µm, thick, asci: clavate, 8-spored ascospores: hyaline, simple, +broadly ellipsoid, 6-11 x 5-7 µm Pycnidia: immersed, 150 x 50 µm; ostioles: brown; conidiophores: type III of Vobis (1980) conidia: filiform, curved, 15-25 µm long Spot tests: cortex K-, C-, KC+ yellow, P-; medulla (in typical chemotype) K+ yellow, C+ yellow, KC+ orange-yellow to pink-orange; P- or + yellow, rarely with a region just above the lower cortex turning P+ orange Secondary metabolites: cortex with placodiolic and usually usnic acid; medulla typically with terpenoids AA and AB and unknowns "LOP-1 and LOP-2", an accessory, P+ orange pigment; there are several other chemotypes, with various other unknowns in addition to or instead of the typical ones, and sometimes without terpenoids or with additional unidentified terpenoids. Substrate and ecology: on hard, non-calcareous rocks, often on steep, shaded rock faces near streams, in pinyon-juniper-grassland to oak or pine-fir forests at 1200-3000 m World distribution: North America and possibly Asia Sonoran distribution: Arizona, Chihuahua, and Baja California Sur. Notes: Lecanora opiniconensis frequently occurs with Rhizoplaca subdiscrepans, from which it is easily distinguished by having epruinose discs and a more deeply yellow upper surface. Other Rhizoplaca species, and Lecanora muralis, and L. polytropa, are easily distinguished from L. opiniconensis by a number of morphological and anatomical features, as well as by chemistry (lack of placodiolic acid). Lecanora opiniconensis is somewhat similar to L. phaedrophthalma, but usually can be distinguished by: 1) areoles +peltate and squamulose, often composed of clusters of smaller secondary subunits; 2) lobes broader, flatter, less divided, and loosely appressed; 3) discs uniformly colored and more yellow; 4) color of the lobe tips and apothecial margins more yellow to orange than the main part of the thallus (more evident in herbarium); 5) apothecial margins rather prominent and persistent. Several main chemotypes and morphotypes are presently included under L. opiniconensis; the western populations (including those in our region) are much more variable in morphology and especially in chemistry (sometimes lacking terpenoids, and with a wide range of unknown phenolic substances) than material from the Great Lakes region. While some Sonoran collections are indistinguishable from eastern material, in others (mainly in very shaded sites) the thallus and frequently consist of +scattered squamules, or becomes strongly contorted towards the center; the upper surface is paler, more grayish, mostly dull and even slightly pruinose; and the discs are often rather pale yellow. Forms with poorly developed thallus might be confused with L. geiserae; see notes under that species. Most of the variants appear to be environmentally induced and connected by intermediates, apparently with no consistent correlations between chemistry and morphology. A peculiar morphotype with at least partly red-brown discs, as in L. phaedrophthalma, but otherwise more like L. opiniconensis, occurs in areas just outside our region.