Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.

Thallus: rimose to areolate, up to c. 0.2 mm thick, with fine fissures, without a well-defined margin, lacking a prothallus areoles: angular, plane, 0.2-0.4 mm wide surface: grayish white, dull, minutely roughened to subfarinose anatomy: upper cortex and epinecral layer hardly discernible, scurfy; algal layer: irregularly thick (up to 200 µm), with algal cells 7-12 µm in diam., densely sprinkled with substrate crystals especially in lower parts; alga-free medulla: chalky white, grading with the decomposed rock surface Perithecia: semi-immersed, hemispherically prominent, black; exciple: (sub)globose, 0.25-0.40 mm wide, black, 20-25 µm thick; involucrellum: hemispherical, extending halfway to two-thirds down the exciple, contiguous with the exciple, laterally 50-70 µm thick, at the base equally thick or slightly thinning; periphyses 35-45 µm long, thin, sparingly branched asci: clavate, 70-75 x 20-25 µm, 8-spored ascospores: hyaline, simple, ellipsoid, 19-25 x 9-12 µm Pycnidia: unknown Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: thinly epilithic, on carbonate rock World distribution: widely distributed in Europe and rare in southwestern North America Sonoran distribution: found once in Arizona (Gila County). Notes: The sample is scanty but typical. Verrucaria schindleri is superficially similar to V. muralis, from which it is separable on account of its dark exciple; the exciple is blackish brown even in thin sections.