Life habit: lichenized Thallus: crustose, coherent but when in bark usually incoherent, 0.05-0.2 mm wide surface: white to whitish-gray to gray brownish-gray, smooth or finely rugose, epruinose; soredia present or absent cortex: inconspicuous or missing medulla: absent or indiscernible photobionts: primary one a Trentepohlia, secondary photobiont absent Ascomata: apothecioid, numerous, solitary, elongated or circular in outline, sessile rarely immersed with base usually not constricted, between (0.15-) 0.5 (-1.3) mm diam.; disc: exposed, convex to nearly flat, rarely concave, pruinose rarely epruinose but pruina may disappear with age in some species; exciple: present but usually poorly developed and on old ascomata often dislocated; cortex: absent; algae: missing or sporadically present; proper exciple: a thin parathecium, rarely inconspicuous, plectenchyma in most species of loosely intertwined hyphae or in some species with hyphae anticlinally arranged; epithecium: brown; hymenium: up to 80 µm thick, paraphysoids unbranched or only sparsely branched, hyaline; hypothecium: dark-brown (carbonaceous) rarely pale brown or hyaline, extending down to substrate asci: clavate, 50-80 x 10-15 µm ascospores: fusiform or acicular-fusiform, hyaline, 3-septate; walls: smooth Conidiomata: pycnidial, solitary, immersed or slightly sessile, black or brown, c. 0.05-0.15 mm diam. conidia: bacilliform rarely filiform, curved, hyaline or rarely pale brownish olive-green Secondary metabolites: aliphatic acids, beta-orcinol depsides Geography: subtropical to temperate regions Substrate: on bark. Notes: Tehler (1993a) reported only one species in Schismatomma for California. Several other species formerly placed in Schismatomma were excluded from the genus, but were not recombined to their proper genera because their taxonomic placement was unknown. One of those species, Schismatomma pluriloculare (Zahlbr.) Zahlbr., occurs in the Sonoran region and thus is provisionally treated here.