Thallus: crustose, usually thick, at first comprised of discrete, plane areoles up to 0.4-0.8 mm diam., becoming contiguous and thallus continuous, rugose surface: light gray, dull; margin: determinate or indeterminate; prothallus: present or absent, dark, entire; vegetative propagules: absent Apothecia: sessile, frequent, sometimes becoming contiguous, up to 0.7-0.8 mm in diam. disc: light to dark brown, plane becoming convex thalline margin: concolorous with thallus, entire, becoming flexuose by compression, persistent, c. 0.1 mm wide; excipular ring: absent thalline exciple: 60-70 µm wide laterally; cortex: 15-30 µm wide, columnar; cortical hyphae: up to 4-5.5 µm wide, not pigmented; algal cells: up to 8-10 µm in diam.; thalline exciple: (50-)80-100 µm wide below; cortex: 2540 µm wide, also columnar proper exciple: hyaline, c. 5 µm wide, expanding to 20-25 µm at periphery hymenium: 70-110 µm tall, oil paraphyses sometimes present; paraphyses: 1.5-2.5 µm wide, conglutinate, with apices to 3-5.5 µm wide, lightly pigmented forming a light to dark brown epihymenium; hypothecium: hyaline or pale yellow, 80-130 µm thick asci: clavate, 50-65 x 18-22 µm, 8-spored ascospores: brown, 1-septate, ellipsoid, type A development; Pachysporaria-type, (17-)20-21.5(-24.5) x (9-)10.5-11.5(-13) µm, lumina irregularly polygonal at first, becoming irregularly rounded, walls remaining thick, slightly waisted at maturity; torus: narrow; walls: ornamented or not Pycnidia: immersed; conidiophores: type I conidia: bacilliform, 4-5.5 x c. 1 µm Spot tests: K+ yellow, C-, KC-, P+ faintly yellow Secondary metabolites: atranorin in cortex. Substrate and ecology: collected on Alnus in a riparian habitat at 1720 m; in Europe it occurs on rough barked trees, particularly Quercus World distribution: western Europe (Scotland to Portugal and Italy, Madeira and the Canary Islands), and Mexico Sonoran distribution: Chihuahua, localized Sierra Madre Occidental distribution. Notes: Rinodina roboris is characterized by its thick thallus with atranorin in the cortex, large apothecia with flexuose margins, and Pachysporaria-type spores. The paraphyses are unusually narrow and the presence of oil paraphyses is rare among North American species. The collections are unusual in that the apothecial discs, epihymenium and spores are all lightly pigmented by comparison with European specimens. New to North America, previous records (Herre 1910, Hasse 1913, Fink 1935) are misidentifications.