Thallus: deeply cracked-areolate, forming small patches between other crustose lichens or forming extensive colonies up to several centimeters across, 0.20-0.80 mm thick, with rather broad fissures, with abrupt margins or thinning at margins, sometimes bordered by a thin black prothallus areoles: angular in outline, plane, 0.3-1 mm across, sometimes basally slightly constricted, with black side walls of mature areoles, partly subdivided into a mosaic of smaller units by thin dark lines surface: gray or pale brown, dull, minutely roughened, ±whitish gray pruinose, ±crossed by dark lines along which the areoles tend to divide anatomy: upper cortex: poorly defined, composed of small cells (uppermost ones brown pigmented), overlain with a thin amorphous epinecral layer; algal layer: discontinuous, divided by thin black tissue into small pockets, with algal cells 4-8 µm in diam. in distinct vertical columns reaching down to the black carbonaceous basal layer which may occupy half or more of thallus thickness; mycobiont portion: paraplectenchymatous Perithecia: fully immersed within the areoles, few to many in each areole, arising within the algal units with their apices appearing at thallus surface as blackish flat or slightly convex discs; exciple: subglobose, 0.18-0.30 mm wide, dark brown, c. 15 µm thick, scarcely distinguishable from the involucrellum; involucrellum: 30-50 µm thick, extending to exciple-base level and fusing with the carbonaceous basal layer; periphyses 20-25 µm long asci: clavate, 55-65 x 15-20 µm, 8-spored ascospores: hyaline, simple, ellipsoid , 11-16 x 5-7 µm Pycnidia: immersed, ovoid, c. 100 µm high, 50 µm wide conidia: bacilliform, c. 5 µm long Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: epilithic, on non-calcareous rocks in open situation World distribution: Europe and North America Sonoran distribution: Arizona. Notes: The species is a member of the V. fuscella-group which is represented by three similar species in North America. They all share their deeply cracked thalli with areolae more or less mosaic-like subdivided by thin dark lines, often black-rimmed, whitish-gray pruinose upper-sides, and the development of a conspicuous black basal layer which often occupies more than half of the thallus thickness. Verrucaria fuscella lacks an involucrellum. Verrucaria subdivisa has much larger ascospores. The description above follows Zschacke's later use of the name based on his material. Potentially, based on the original description, the original material may prove to be different, but the type was not available at this time. If so, then a new name would be required for the Sonoran material.