Thallus: crustose, thin or evanescent, rimose but often with discrete, scabrid areoles, or areoles well developed, plane or verrucose, up to 0.2-0.7 mm wide surface: dark gray to gray-brown, dull; margin: determinate or indeterminate; prothallus: sometimes present, fimbriate, dark brown; vegetative propagules: absent Apothecia: adnate, frequent and sometimes contiguous, up to 0.25-0.6(-0.8) mm in diam. disc: black, plane, sometimes becoming markedly convex thalline margin: concolorous with thallus, 0.05-0.1 mm wide, entire becoming excluded; excipular ring: absent thalline exciple: 20-100 µm wide laterally; cortex 5-10 µm wide; sometimes with epinecral layer: 5-10 µm thick; cortical cells: up to 4.5-7.5 µm wide, pigmented or not; algal cells: up to 8.5-14.5 µm in diam.; thalline exciple: 30-100 µm thick below; cortex 10-15 µm proper exciple: 5-20 µm wide laterally, expanded to 20-30(-55) µm at periphery hymenium: 70-90 µm tall, paraphyses: 1.5-2.5 µm wide, not conglutinate, with apices expanded up to 4-6.5 µm wide, darkly pigmented, forming a dark brown epihymenium; hypothecium: hyaline, 30-70 µm thick asci: clavate, 40-60 x 12-19 µm, 8spored ascospores: brown, 1-septate, broadly ellipsoid, type B development, Dirinaria-type, (11.5-)14-15(-17.5) x (6-)7.5-8.5(-9.5) µm, apical walls not or hardly thickened at maturity, narrowly swollen at septum in large spores, some spores swelling at septum in K; torus: absent; walls: lightly ornamented or not Pycnidia: immersed in thallus conidia: bacilliform, 4-6 x c. 1 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: frequent on maritime rocks and on eutrophic rocks used as bird perches in coastal regions World distribution: widely distributed on maritime rocks in temperate regions of the Northern and Southern Hemispheres, more rarely on calcareous substrates inland in Europe Sonoran distribution: Channel Islands, coastal California and Guadalupe Island, Baja California. Notes: Rinodina gennarii is remarkable for the degree of variability shown by its thallus morphology and spore size. The thallus, that may be evanescent, is usually continuous or rimose with a scabrid appearance, but may also be well developed with verrucose areoles. The thallus may also vary in color from light gray to gray-brown, such color variation being seen within a single thallus on different exposures. Its habit may be similar to that of R. innata and R. pacifica that possess larger Physcia-, and Physconia-type spores, respectively, each with a prominent pigmented torus at maturity. Rinodina innata, that has been collected with R. gennarii above the spray zone, is otherwise distinguished by its innate apothecia. Rinodina pacifica has larger apothecia and a brown thallus.