Thallus: crustose, very thin, membranaceous to uneven or almost disappearing to granular and uneven, occasionally finely scurfy-effuse to granular-leprose or immersed; prothallus: white surface: pale to dirty gray-green or white, rather smooth to wrinkled and roughened, partially shiny, partially dull cortex: not developed medulla: indiscernible Apothecia: very numerous, scattered to crowded, appressed, emergent to sessile, 0.2-0.4(-0.5) mm in diam, sometimes several confluent disc: pale or sordid red, pale yellow, pale pink, reddish brown, or almost black, rarely white, +translucent to pale yellowish and dark-spotted when wet, plane to convex, becoming markedly convex, epruinose margin: rather thin, level with disc, smooth to crenulate, often becoming incomplete and excluded, white or pale gray,.up to c. 0.05 mm wide amphithecium: without a cortex or epinecral layer, with algal cells filling the entire margin parathecium: not or weakly developed epihymenium: pale brown, often with fine pigment granules hymenium: hyaline, 30-50 µm tall; paraphyses: rather strongly coherent, simple, 1.5-2 µm wide, the tips pale to brown, 2-3(-4) µm wide; hypothecium: hyaline, with intricate hyphae, 25-70 µm thick asci: clavate or inflated-clavate, 30-40 x 10-12 µm, 8-12(-16)-spored even in the same apothecium ascospores: hyaline, (0-)1(-3)-septate (the septum distinct), narrowly ellipsoid, oblong to almost fusiform to generally slightly curved when mature, 9-14(16) x (3-)4-5 µm Pycnidia: rare, immersed, pale brown in upper part, hyaline below conidia: filiform, curved, 17-20 x 0.5 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on nutrient-rich, subneutral to moderately acidic bark (especially Acer, Fraxinus, Populus, Quercus twigs, Sambucus), and mostly associated with Xanthoria-dominated communities; also on Cupressus and Eucalyptus and shrubs in coastal areas World distribution: widely distributed in Europe and North America, Australia, and New Zealand Sonoran distribution: southern California, from Monterey Co. south to the Channel Islands. Notes: In contrast to the opinion of some other authors, L. cyrtella is clearly different from L. cytellina, but the latter species has not been reported from the Sonoran area. For differences between L. cyrtella and L. fuscelloides, see under the latter species. Cliostomum griffithii differs in having conspicuous black pycnidia, short simple conidia, Biatora-type asci and a distinct chemistry with atranorin and roccellic acid.