Thallus: effuse, ±continuous, thinning at margin, central parts 0.10-0.15 mm thick surface: grayish green, dull, uneven anatomy: upper cortex of 1-2 cell layers, c. 10 µm thick, hyaline; algal layer: densely packed, filling most of thallus thickness, with algal cells 7-11 µm wide, mycobiont portion paraplectenchymatous, composed of polygonal cells 5-10 µm in diam., lowermost part of thallus partly filamentous with hyaline hyphae 3-4 µm in diam., penetrating into the bark Perithecia: deeply immersed in the bark, laterally covered by thallus tissue with only the uppermost part emergent; exciple: 0.28-0.37 mm wide, subglobose, pale, c. 20 µm thick; involucrellum: thin, entirely appressed to the exciple, reaching halfway or deeper down the exciple, in upper part c. 25 µm thick, thinning towards the base; periphyses 25-35 µm long, thin, simple asci: clavate, 8-spored, 90-110 x 25-30 µm ascospores: hyaline, simple, ellipsoid, 24-28 x 11-13 µm Pycnidia: unknown Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: overgrowing bark and bryophytes thereon World and Sonoran distribution: known only from the type collection in Arizona. Notes: Verrucaria quercina comes close to V. phloeophila and V. sorbinea, but these species differ in having simple perithecial walls (i.e. involucrellum lacking or indiscernibly fused with the exciple).