Thallus: foliose, sometimes pulvinate, 2-8 cm in diam., loosely adnate, irregularly lobate lobes: irregular, partly anastomosing, swelling markedly when wet, 2-5 mm wide, 250-400 µm thick; apices: rotund to oblong, thickened, +undulate, entire, lobulate or isidiate upper surface: pale to medium gray, rarely darker gray, usually dull, +granular, laminately ridged, isidiate or minutely phyllidiate (especially along the wrinkles) isidia: scattered to very dense, usually laminal but sometimes marginal, cylindrical to coralloid or flattened, simple, concolorous with the thallus or darker internal anatomy: with upper and lower cortices consisting of a single layer of irregularly isodiametrical cells 4-7 µm in diam., internally with loosely interwoven chains of Nostoc and hyphae lower surface: pale to medium gray, wrinkled, with scattered tufts of white hairs Apothecia: rare, submarginal, substipitate to stipitate, 2.5-8 mm wide disc: orange-brown to red-brown or cream-colored, concave to plane or convex margin: thalline, concolorous with the thallus, wrinkled, usually isidiate exciple: euparaplectenchymatous, 45-90 µm thick centrally hymenium: hyaline below and thinly yellow or brown above, 90-135 µm tall; paraphyses: unbranched, 1-2 µm wide, slightly inflated apically; subhymenium: yellow to pale brown, 35-70 µm thick asci: cylindrico-clavate, 8-spored ascospores: hyaline, muriform, 3-5-septate transversely, 0-1-septate longitudinally, ellipsoid to sub-fusiform, 30-40 x 10-17 µm Pycnidia: not observed Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: usually on bark of moist, montane forests, rarely on rocks World distribution: widespread in the tropcis in North and South America, Australasia, and East Africa, and extending into coastal, western Europe Sonoran distribution: Arizona, Baja California Sur and Chihuahua. Notes: Superficially dark forms of L. coralloideum and L. millegranum are similar but the former is usually typically gray and the latter dark olive green. Furthermore, L. millegranum has granular isidia on a heavily wrinkled (not laminate) thallus, although small incomplete thalli of the two may be very difficult to distinguish. Leptogium coralloideum is considered the isidiate counterpart of L. phyllocarpum.