Thallus: cracked-areolate, often with elongate, incised-lobed marginal areoles, 0.20-0.45 mm thick, forming small patches among other crustose lichens or extensive colonies up to several centimeters wide, usually with a conspicuous black basal layer, with a thick and abrupt margin surface: gray to grayish brown, whitish gray pruinose, dark-edged, subdivided by thin dark lines anatomy: upper cortex: poorly defined, composed of a single layer of brownish cells 4-6 µm in diam. continuing down along the sidewalls of the areoles; algal layer: paraplectenchymatous, composed of cells 3-5 µm in diam., with algal cells 6-13 µm in diam. filling most of the thallus, often with brown to black basal layer up to 200 µm thick (but discontinuous in thin samples) Perithecia: usually several to many per areole, immersed within the algal thallus units that are separated by dark lines, fully immersed with apices plane and level with surface of areole to slightly convex; exciple: subglobose or ellipsoid, 0.2-0.25 mm wide, colorless to brownish, brown to blackish and slightly thicker around the apex; involucrellum: lacking; periphyses c. 20 µm long, simple asci: clavate, 40-50 x 14-17 µm, 8-spored ascospores: hyaline, simple, narrowly ellipsoid, 11-15 x 5-6.5 µm Pycnidia: immersed, 50-70 µm wide conidia: bacilliform, 3-5 x c. 1 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: epilithic, on calcareous or superficially calciferous rocks (granite, rhyolite, rimrock outcrops), mostly montane World distribution: Europe and North America; but reports in the literature unreliable due to the confusing nomenclature which was recently clarified by Orange (2000) Sonoran distribution: Baja California Sur, Chihuahua, and Sonora. Notes: The very similar Verrucaria canella, with much larger ascospores, is reported from western North America, but could not be confirmed for the study area.