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

Thallus: cracked-areolate, up to 0.35 mm thick including a prominent black basal layer that occupies the lower two-thirds of the thallus thickness, with narrow fissures areoles: angular, plane, 0.2-0.4 mm wide, secondarily subdivided by thin fissures surface: dark brown to black, dull, rough to granular anatomy: upper cortex not developed, only uppermost cell layer brown pigmented; algal layer: discontinuous, forming small pockets up to 100 µm thick, with algal cells 5-10 µm in diam.; mycobiont portion: paraplectenchymatous, composed of cells 4-8 µm in diam.; resting on the black basal layer Perithecia: entirely immersed in thallus with only the black apical portion showing; exciple: subglobose, 0.20-0.25 mm wide, dark, 15-20 µm thick; involucrellum: appressed to the exciple and hardly discernible from it, laterally 50-70 µm thick, extending down to exciple-base level and fusing with the black basal layer; periphyses 20-25 µm long asci: clavate, 8-spored ascospores: hyaline, simple, ellipsoid , 15-20 x 7.5-11 µm Pycnidia: unknown Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: epilithic, on siliceous rocks World distribution: previously known from central and southern Europe Sonoran distribution: southern California (Santa Catalina Island). Notes: Verrucaria asperula is similar to V. nigrescens, from which it differs mainly in the rough upper surface of the thallus (smooth in V. nigrescens).