Thallus: foliose, orbicular to irregular, fragile, up to 2 cm diam, ± firmly adnate, central parts often covered by pustules dissolved into granulate soredia lobes: flat to concave, up to 0.5 mm broad, rarely broader, sparsely divided; tips: truncate or crenulate, occasionally ascending upper surface: whitish, rarely dark gray, usually dull pustules or isidia: laminal, often developing into granular soralia or craters that may fuse and cover the whole thallus upper cortex: paraplectenchymato lower cortex: ± prosoplectenchymatous, pale to brownish (inner parts) lower surface: white at the tips, darker in inner parts; rhizines: few, concolorous with the underside Apothecia: frequent, up to 2 mm diam., margin often crenulate ascospores: brown, 1-septate, Pachysporaria type, (16-) 18.5-22 (-23.5) x (7.5-) 8.5-10 (-11) µm Pycnidia: not seen Spot tests: upper cortex and medulla K+ yellow, C-, KC-, P+ yellow Secondary metabolites: upper cortex with atranorin; medulla with atranorin, lecotylin and traces of other triterpenoids visible in TLC. Substrate and ecology: growing mainly on trees but also on rocks in open sites World distribution: known from scattered localities in central and southern Europe and from southern California Sonoran distribution: known only from the Channel Islands of southern California and the adjacent mainland.