Thallus: crustose, thin to thick, continuous, ±rimose or without cracks surface: pale gray or pale yellow, pale green, or bluish gray, smooth, wrinkled, or warted cortex: a ±well-developed phenocortex and epinecral layer Apothecia: at first flat, remaining so or eventually becoming convex, 0.2-0.8(-1.7) mm in diam. disc: pale pink, gray-violet, purple-brown, or brownish or purplish black, or pure black (often piebald), often with thin white pruina margin: concolorous with disc or paler, rarely uppermost part of margin darker than disc, distinct, raised above disc in young apothecia, soon level with disc, persistent or sometimes finally excluded, without a thalline margin exciple: laterally 30-50 µm wide, with numerous small crystals (soluble in K), colorless, pale yellow (K+ intensifying), or pale brown to red-brown to black-brown (K+ purplish), fading below hypothecium: colorless or pale yellow (K+ intensifying) epithecium: colorless or ±brown (K+ purplish), inspersed with small crystals (soluble in K) hymenium: hyaline, 45-60 µm tall; paraphyses: c. 1.5 µm wide in mid-hymenium; apices: ±clavate, 2-6 µm wide, at least some with distinct hoods of brown pigment when pigment is present in the epithecium asci: clavate, 8-spored ascospores: hyaline, 1-septate (very rarely 3-septate), each cell often with 1-3 oil droplets, narrowly ellipsoid or oblong, straight or slightly curved, 8-16 x 3-5 µm Pycnidia: often abundant, ±immersed or almost sessile, black, often widely gaping and irregularly shaped, sometimes regular and with a distinct ostiole, 100-300 µm in diam., starting as unilocular but sometimes becoming multilocular with age conidia: drop-shaped to almost bacilliform, simple, 3-5 x 1.3-2 µm Spot tests: K+ pale yellow, C-, KC-, P+ pale yellow Secondary metabolites: atranorin, chloroatranorin, roccellic acid, sometimes caperatic acid, one or two unidentified fatty acids in the thallus., and usnic acid (trace [Kantvilas and Elix 1995]). Habitat and ecology: on bark of deciduous trees and shrubs at low elevations (up to c. 500 m) World distribution: North America, Europe, Africa, East Asia, and Australia Sonoran distribution: widespread along the coast of southern California and Baja California. Notes: Whereas North American Cliostomum griffithii is dominated by unilocular pycnidia, European material often possesses multilocular ones. The difference is not clear-cut, however.