Thallus: crustose, thick, areolate, areoles up to 0.6-1 mm wide, sometimes with sublobate margins, plane or tumid surface: dark gray to dark gray-brown, shiny; margin: determinate or indeterminate; prothallus: lacking; vegetative propagules: absent Apothecia: erumpent or innate at first, becoming adnate, frequent, scattered or contiguous, up to 0.6-0.8 mm in diam. disc: black, plane, sometimes becoming slightly convex and fissured thalline margin: concolorous with thallus or lighter at first due to broken epinecral layer, 0.05-0.15 mm wide, entire and persistent; excipular ring: absent thalline exciple: 70-100 µm wide laterally; cortex: 5-20 µm wide; epinecral layer: 5-10 µm wide; cortical cells: up to 5-7.5 µm wide, pigmented; algal cells: up to 12-17.5(-30) µm in diam.; cortex: sometimes expanded below to 40 µm wide, cellular proper exciple: hyaline, c. 10 µm wide laterally, expanded to (10-)20-25 µm at periphery hymenium: 85-110 µm tall; paraphyses: 2.5-3 µm wide, not conglutinate, with apices up to 4.5-6.5 µm, darkly pigmented, forming dark brown epihymenium; hypothecium: hyaline, 40-80 µm thick asci: clavate, c. 50 x 20 µm, 8-spored ascospores: brown, 1-septate, broadly ellipsoid, type A development, Physconia-type, (15.5-)1819(-22) x (8.5-)10-10.5(-12) µm, thin walled from start, broad lumina canals only evident in young spores, becoming waisted at maturity; torus: absent but darkly pigmented septal wall may suggest a dark torus in mature spores; walls: ornamented Pycnidia: immersed; conidiophores: type I or VI conidia: bacilliform, 5-6.5 x c. 1.5 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on steppe shrubs, deciduous trees, conifers and wood World distribution: a North American endemic with a distribution centered on the Colorado Plateau Sonoran distribution: Arizona in Coconino and Navajo Counties at elevations of 2015-2730 m. Notes: Rinodina grandilocularis is characterized by Physconia-type spores with large lumina and thin walls from an early stage of development. The species is further characterized by the gray-brown color and typically shiny surface of its well developed thallus, and by its relatively large apothecia with margins lighter in color than the thallus due to flaking of the epinecral layer. Rinodina juniperina has a similar thallus with an epinecral layer, but its areoles usually possess marginal consoredia, and it has smaller, Physcia-type spores.