Thallus: effuse to determinate, continuous to sparingly and irregularly rimose, thin (0.10-0.15 mm thick), with fine fissures, crowded with many small perithecia, without an apparent prothallus areoles: polygonal, plane, 0.2-0.5 mm wide surface: grayish brown, pale brown or brown, smooth, dull to somewhat shiny anatomy: undifferentiated, densely filled with algal cells 6-8 µm in diam. Perithecia: ?-immersed to prominent, dense; exciple: subglobose, 0.15-0.20 mm wide, colorless, 15-20 µm thick; involucrellum: hemispherical or broadly conical, extending to exciple-base level, 35-50 µm thick at base, slightly thinner near the apex, contiguous with the exciple in upper part, often ±diverging in lower half; periphyses 15-20 µm long, thin, simple asci: clavate, 50-60 x 17-21 µm, 8-spored ascospores: hyaline, simple, ellipsoid , (15-)16-19 x 6-8 µm Pycnidia: unknown Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: epilithic, on schist, montane, in canyon and cliffsides World distribution: Europe and northwestern Mexico Sonoran distribution: Sonora. Notes: Verrucaria olivacella is very similar to V. dolosa with equally sized perithecia, but the latter species has smaller spores. Verrucaria floerkeana shares the spore-size with V. olivacella but has larger perithecia. Verrucaria amylacea has a thicker involucrellum. Verrucaria pinguicula A.Massal., which is not known from the region, has thicker thalli with fully immersed, apically flattened perithecia, a thicker involucrellum and narrower spores. The correct name might be Verrucaria contardonis Servít, but the type is in very poor condition. Its thallus is paler, and it was collected from limestone.