Thallus: inconspicuous, when epilithic somewhat farinose, thin, uneven, discontinuous, irregularly rimose in parts, without a prothallus; areoles: if present at all, angular to irregular, 0.3-0.7 mm wide surface: whitish gray to tawny, having about the same color as the substrate anatomy: upper cortex not discernible, algal layer within the decomposed upper zone of the rock; algal cells: 7-11 µm in diam.; hyphae: obscured by substrate grains Perithecia: superficial, hemispherically prominent, black, rough, with a thin thalline covering at their bases and sometimes also on lateral parts, or subpruinose; exciple: subglobose, 0.3-0.5 mm wide, 20-30 µm thick, colorless or pale brownish, dark only around ostiole, sometimes an inner layer darkening in old perithecia; involucrellum: on upper third, at the most extending down to mid-level of the perithecium, more or less diverging from the exciple, apical part 50-80(-100) µm thick, usually thinning basally; periphyses 40-60 µm long, thin, finely branched-anastomosing asci: clavate, 80-100 x 25-30 µm, 8-spored ascospores: hyaline, simple, ellipsoid, 23-30 x 12-15 µm Pycnidia: unknown Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: semi-endolithic or thinly epilithic, on or in limestone and sandstone World distribution: Europe and North America Sonoran distribution: southern California (Santa Barbara and Ventura Counties, Chanel Islands). Notes: Verrucaria papillosa is similar in overall appearance, but has dark exciples, and an involucrellum that extends down to the lower part of the perithecium. Verrucaria muralis has smaller spores, shorter periphyses, and the involucrellum is usually not spreading.