Thallus: foliose, orbicular, rosette-forming, 10-50(-85) mm in diam., loosely attached centrally, with free margins, rather thin and papery, brittle when dry, flabby when moist lobes: rather broad, rounded, 5-20(-30) mm in diam., discrete at margins or shallowly imbricate, shallowly to deeply incised; margins: entire, not thickened below, wavy, slightly crisped and subascendent above, occasionally to commonly with minute, silky, white to pale brown, glistening tufts of tomentum upper surface: dark blue-black to glaucous blue-gray when moist, pale gray-blue when dry, smooth, undulate to shallowly punctate-impressed, dull or rarely glossy in parts, minutely velvety-pilose in parts (x10 lens), with minute, white, scattered maculae best seen when moist (x10 lens), without isidia, phyllidia or soredia medulla: white, K- photobiont: cyanobacterial lower surface: white at margins, pale buff to pale brown centrally, dull, minutely wrinkled, tomentose from margins to center; tomentum: white to pale brown, silky, sparse to dense and uniformly felted cyphellae: common, scattered, round to irregular, 0.1-1(-1.5) mm in diam., with very narrow margins, sharply defined, rising abruptly from cortex, with a brilliant white basal membrane Apothecia: occasional to frequent, commonly developed and often clustered at or towards margins in small groups (reminiscent of Sticta ambavillaria from East Africa), rounded (0.2-)0.52(-4) mm in diam.; disc: yellow-brown to pale red-brown, dull, plane to slightly convex, epruinose margins: white, thin, entire to crenulate, paler than disc and very slightly raised above surface of disc, velvety-pilose [often visible at margins of disc (x10 lens)]; epihymenium: pale yellowish brown, 7-12 µm thick hymenium: hyaline, 60-75 µm tall; hypothecium: pale yellow-brown, opaque, 45-80 µm thick asci: clavate, 52-65 x 12-18 µm ascospores: hyaline, 13-septate, straight or slightly curved, fusiform-ellipsoid with pointed apices, (22-)26-32(-36) x 7-8.5(-10) µm Pycnidia: occasional, scattered at lobe margins, visible as pale white or fawn-colored swellings, 0.5-1 mm in diam., with a central, red-brown, punctiform ostiole conidia: bacilliform, straight, 4-5 x 1 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on bark in pine-oak forest, pine-fir forest on Pinus cembroides, Quercus rugosa, Q. scytophylla, and on rhyolite outcrops, 1950-3050 m World distribution: neotropics and palaeotropics, Jamaica and Mexico south to Peru and Brazil, eastern and southern Africa, St Helena, Madagascar, and Hawaii Sonoran distribution: rather common in Chihuahua and Sonora. Notes: Typification of this species is discussed in Galloway (1994b: 47). Useful notes are given in Tuckerman (1882: 98), and a bibliography of published reports of in Mexico is listed in Imshaug (1956: 340).