Thallus: placodioid, moderately tightly attached to substrate, verrucose-areolate centrally; marginally lobate, areoles: partly somewhat foveolate-plicate, becoming lobate, 1-3 mm thick, up to 1-2 mm broad lobes: short, broadened towards tips, moderately and coarsely crenate-incised (flabelliform), up to 2.5 mm long, 0.5-1 mm broad; ultimate segments: 0.3-0.5 mm wide, plane to slightly convex, partly almost somewhat plicate, 0.2-0.3 mm thick surface: moderately yellow to grayish yellow, light olive to brownish gray, or moderately olive-brown, slightly more brown on lobe tips, dull, or slightly shiny (waxy), epruinose upper cortex: containing some dead algae, the upper (20-)25-30 µm interspersed with pale yellow granules (soluble in K), with anticlinally oriented hyphae, c. 2 µm thick, with lumina 2-3 µm long and 0.5-1 µm wide, with a c. 5 µm thick epinecral layer, overall (25-)30-40 µm thick medulla: containing grayish granules at least in the lower part; algal layer: +continuous, (40-)50-75 µm thick; algae: 7-10(-12) µm in diam. lower cortex: present at least towards lobe tips, similar to upper one Apothecia: common, irregular, borne submarginally, one to several per areole, sessile, +constricted, up to 3 mm in diam. disc: dark brown with red tinge, plane, epruinose margin: strongly flexuous or sinuous and coarsely crenate towards the inside, slightly raised, persistent, 0.2-0.3 mm wide, somewhat irregularly broadened, concolorous with thallus, dull; parathecial crown: not evident amphithecium: present, with a continuous to interrupted algal layer 50-75 µm thick and extending under the hypothecium, with grayish granules in the medulla, corticate; cortex: the outer 30 µm inspersed as in thallus, thinning slightly on lower side, with an epinecral layer c. 5 µm thick, overall c. 50 µm thick parathecium: hyaline, with conglutinated hyphae, c. 5 µm thick and with lumina c. 1 µm thick epihymenium: interspersed with fine brown granules (soluble in K), covered by 5 µm thick hyaline layer, 15-25(-35) µm thick hymenium: heavily inspersed with oil droplets almost throughout, and also containing some reddish granules, 65-85 µm tall; paraphyses: coherent, 1-1.5 µm in diam. below, the tips scarcely thickened; subhymenium: yellowish brown, with oil droplets, c. 50 µm thick; hypothecium: 12-20 µm thick asci: clavate, c. 50 x 15 µm, 8-spored ascospores: hyaline, simple, ellipsoid to broadly ellipsoid, 8-10(-12.5) x 5-7 µm Pycnidia: common, 150-200 µm in diam., with rather large ostioles (0.1 mm), only slightly darker and greener than thallus, with a pale wall pale conidia: filiform, rather thick and blunt-tipped, (20-)30-35(-45) µm long Spot tests: thallus K-, C-, KC+ yellow, P-, IKI-; medulla KC- Secondary metabolites: upper cortex with placodiolic acid (major), sometimes with a trace of usnic acid; medulla with none detected or sometimes unknowns. Substrate and ecology: on granite rock, occasionally spreading onto moss World and Sonoran distribution: as described only known from Kern County, California at 920 m just outside of the Sonoran region. Notes: Thomson and Nash (1976) compared L. collatolica to L. christoi W. Weber (= L. phaedrophthalma var. christoi), stating that their new species differed from the latter in usually lacking rosette-like marginal lobes and having a different thallus color (olive instead of yellow) and chemistry (supposedly having α-collatolic acid but based on misidentification of another substance (probably placodiolic acid) by microcrystalline tests [J.A. Elix, personal communication]). However, as pointed out by Weber (pers. Comm., 1976-1988), L. collatolica also shows similarities to L. mellea, and Weber suggested that it might be at most a 'minor chemical variant' of L. mellea. Attempts made in this study to locate additional material of L. collatolica in the vicinity of the type locality in 1985 led to collection of numerous specimens ranging from typical L. mellea to material resembling L. collatolica but differing subtly from the type specimens in morphology as well as chemistry. The type material of L. collatolica has several features that distinguish it from typical L. mellea: 1) thick, mound-like thallus with rather broad and weakly incised lobes, with a more yellow or olive tinge, 2) dark reddish brown discs with thick, prominent and persistent margins, 3) more broadly ellipsoid spores, and 4) presence of placodiolic acid and lack of isousnic acid and fatty acids. The great amount of morphological variability in L. mellea sensu lato is partly correlated with the chemical variability, and strongly suggests hybridization between the two taxa, with introgression of L. collatolica characteristics into L. mellea. However, further investigation is needed to test this hypothesis, and more material of L. collatolica must be seen before this taxon can be properly evaluated. Lecanora collatolica also shows similarities to L. opiniconensis s. lato, but differs from that species especially in the darker, red-brown discs, lack of an orange tinge to the lobe tips, and absence of triterpenoids.