Thallus: cracked-areolate to subsquamulose, 0.2-0.35 mm thick (in vicinity of perithecia up to 0.5 mm) areoles: subangular when young, then roundish with margins often slightly elevated and irregularly sublobulate, partly overlapping, plane (sterile areoles) to slightly convex (when fertile), 0.5-0.8 (-1) mm wide when fertile, sterile ones smaller, with rather wide fissures, sometimes secondarily diffracting into smaller units surface: gray-brown or greenish brown, dull anatomy: upper cortex: poorly defined, consisting of a single layer of light brown, ±round-angular cells 4-7 µm in diam., or sometimes becoming 10-15 µm thick, unevenly delimited against the algal layer; algal layer: 100-200 µm deep, with densely packed algal cells 6-10 µm in diam., mycobiont portion subparaplectenchymatous, alga-free medulla: with looser texture, colorless to pale brown or brown and filamentous in a lower part, with abundant substrate particles Perithecia: single or two per areole, immersed with only the tips slightly protruding; exciple: subglobose, 0.3-0.5 mm wide, pale to brown, 20-30 µm thick; involucrellum: distinct, hemispherical to broadly conical, reaching down to exciple-base level, upper part contiguous with exciple, at the base sometimes slightly diverging from it, inner part partly somewhat paler and patchily pigmented, laterally 40-60 µm thick, ±distinctly broadening up to 100 µm thick at the base and there ±diffuse and grading into the brown medullary tissue; periphyses 30-40 µm long, 2-3 µm thick, simple or scarcely furcate asci: clavate, 85-105 x 27-35 µm, 8-spored ascospores: hyaline, simple, ellipsoid, 24-29 x 13-15 µm Pycnidia: unknown Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: epilithic, on acid or slightly calciferous rocks World distribution: known from few localities in Europe and southwestern North America Sonoran distribution: three records from California (Orange and Riverside Counties), where it was found on sandstone and granite boulders in chaparral or opening. Notes: Verrucaria fuscoatroides has smaller and thinner areoles, and smaller perithecia. There are several superficially similar species in the study area that need further study.