Thallus: crustose, thin, composed of discrete, sometimes sublobate, or contiguous, slightly convex areoles, up to (0.2-)0.5-1 mm wide surface: light gray, dull; margin: determinate or not; prothallus: lacking; vegetative propagules: absent Apothecia: suberumpent becoming sessile, frequent, rarely contiguous, up to 0.5-0.8 mm in diam. disc: black, plane to convex or rarely half-globose thalline margin: concolorous with thallus, 0.05-0.1 mm wide, entire, persistent or becoming thinner by exclusion, rarely excluded, sometimes growing up around proper margin; excipular ring: sometimes present, raised thalline exciple: 60-100 µm wide laterally; cortex: (5-)10-20 µm wide; cells: up to 4.5-6.5 µm wide, rarely pigmented; algal cells: up to 10-13(-18) µm in diam.; thalline exciple: 80-140 µm below; cortex: (20-)35-60 µm thick, columnar, structure occluded by atranorin crystals proper exciple: hyaline or lightly pigmented, 5-15 µm wide laterally, expanding to (10-)15-35 µm at periphery hymenium: 80-100(-120) µm tall; paraphyses: 2-2.5 µm wide, often conglutinate, with apices up to 4-5 µm wide, lightly or heavily pigmented and immersed in dispersed pigment forming a dark, red-brown epihymenium; hypothecium: hyaline, 90-120 µm thick asci: clavate, 60-70 x 16-23 µm, 8-spored ascospores: brown, 1-septate, ellipsoid, developmental type A, Physcia-type, (16-)19-20.5(-23.5) x (8.5-)10-11(-12.5) µm, apical walls remaining thick until very late; torus: narrow; walls: ornamented Pycnidia: infrequent, immersed in thallus with only darkly pigmented ostiole exposed; conidiophores: type I, conglutinate conidia: bacilliform, 4-5 x c. 1 µm Spot tests: K+ yellow, C-, KC-, P- or P+ faint yellow Secondary substances: atranorin in cortex, zeorin (trace) in medulla. Substrate and ecology: frequent on twigs and small branches, a pioneer species on both coniferous and deciduous trees World distribution: southern and central Europe, Macronesia, and western North America (coastal ranges, Sierra Nevada and Rocky Mountains) Sonoran distribution: Arizona and southern California, at elevations of 280-1980 m. Notes: Rinodina capensis was first reported from North America by Magnusson (1953, as R. corticola) but this material has a P+ epihymenium (red crystals of pannarin) and belongs to R. aurantiaca. The two species are otherwise very similar possessing atranorin in the cortex, an expanded, columnar, lower cortex and Physcia-type spores. Rinodina californiensis is distinguished by its Dirinariatype, slightly shorter spores and lack of a columnar lower cortex. Rinodina boulderensis also has atranorin in the cortex but its Physcia-type spores are significantly smaller and are characterized by a prominent, dark torus.