Thallus: crustose, thin and rimose-areolate to thick and rugose-verrucose or even subsquamulose; prothallus: often present, black surface: yellowish white to glaucous gray, smooth, esorediate medulla: white, lacking calcium oxalate (H2SO4-) Apothecia: lecideine, abundant, 0.2-2 mm in diam., sessile disc: black, epruinose, initially flat, soon convex margin: black, initially distinct, later excluded proper exciple: 35-95 µm thick, lacking secondary metabolites; not clearly differentiated into separate parts, dark brown throughout with carbonized cells (<6 µm, HNO3-), transient with the brown, <280 µm thick hypothecium (HNO3-) epihymenium: brown, pigmentation continuous with the outer exciple (HNO3-) hymenium: hyaline, strongly inspersed with oil droplets, 115-165 µm tall; tips of paraphyses: usually <3 µm wide with distinct apical caps asci: clavate, Bacidia-type, 95-112 x 20-40 µm, usually 8-spored ascospores: often remaining hyaline to ±olive, eventually becoming brown, spore apices often remaining unpigmented, muriform, with 13-40 cells in optical section, ellipsoid to oblong, (29.5-)33.7-[39.6]-45.5(-57) x (12.5-)13.3-[15.5]-17.7(-26.5) µm, with apical, lateral and septal wall thickenings (apical thickenings often permanent), proper wall c. 1.2 µm thick; lacking a perispore, ornamentation: not visible in DIC Pycnidia: rare, immersed, with uppermost part protruding, wall mainly pigmented in upper part conidia: bacilliform, 4-6 x 1 µm Spot tests: thallus K-, C+ orange (best seen under the microscope), P-; medulla K-, C-, P- fluorescence: UV+ bright or pale yellow to orange iodine reaction: medulla non-amyloid Secondary metabolites: diploicin (major), isofulgidin (minor), unknown (minor), and 2,5-dichloro-3-O-methylnorlichexanthone (trace). Substrate and ecology: on bark and wood of trunks, branches and twigs of both broad-leaved and coniferous trees and shrubs in open situations along the Pacific coast, such as dune areas, salt marshes, chaparral, and coastal desert World distribution: North America (the Pacific coast and islands between Coos County, Oregon and Baja California Sur) Sonoran distribution: coastal fog zones of southern California, Baja California, and Baja California Sur. Notes: Buellia oidalea is characterized by its large, muriform spores. The species is similar to Buellia oidaliella in most respects but differs by its distinctly larger spores with thickened, often unpigmented apices, its taller hymenium, and the absence of calcium oxalate (in thallus or as a pruina). Zahlbruckner's Cat. Lich. Univ. 7: 454 (1930-1931) cites "Lecidia oidalea Nyl." as an erroneous basionym. Nylander never published a species named Lecidia oidalea. Instead the citation in Zahlbruckner refers to Lecidea aliena Nyl. in Mémoir Soc. Impr. Sienc. Natur. Chebourg 5: 127 (1857), which is a nomen nudum. The name "Lecidia oidalea Nyl." must therefore be disregarded."