Thallus: crustose, thin, discontinuous at first, becoming rimose and sometimes areolate, areoles up to c. 0.6 mm wide, plane becoming uneven surface: light to dark gray, dull; margin: indeterminate; prothallus: lacking soredia: 15-45 µm in diam., often covering large areas of thallus, typically lighter in color than thallus, sometimes with blastidia up to 0.1 mm long Apothecia: adnate, frequent, often contiguous, up to 0.6-1 mm in diam. disc: black or gray pruinose, plane, becoming convex thalline margin: concolorous with thallus, 0.05-0.1 mm wide, sometimes incomplete, poorly developed or becoming sorediate, usually persistent, sometimes excluded; excipular ring: usually prominent, raised thalline exciple: 65-90 µm wide; cortex absent or only one cell thick; cortical cells: up to 4-6 µm in diam., pigmented or not; algal cells: up to 9-13 µm in diam. proper exciple: 10-15 µm wide laterally, expanding to 30-40 µm at periphery, pigmented light yellowish-brown, similar to the hypothecium and hymenium hymenium: 80-120 µm tall; paraphyses: c. 2 µm wide, conglutinate, with apices up to 2.5-4 µm, immersed in pigment, forming light red-brown epihymenium, surficial pannarin crystals present (P+, forming red-crystals) or absent; hypothecium: 40-50(-110) µm thick asci: clavate, 70-110 x 24-39 µm, 8-spored, sometimes only 6 fully developed ascospores: brown, 1-septate, ellipsoid, development type A, Pachysporaria-type, (21.5-)26-27.5(32) x (10.5-)13-14(-16.5) µm, lumina angular (Physcialike) at first, becoming irregularly angular and sometimes transiently polygonal, then irregularly rounded; mature spores slightly waisted; torus: narrow but distinct; walls: not ornamented Pycnidia: not seen Spot tests: K+ faint yellow, C-, KC-, P+ immediately orange-red (cinnabar) Secondary metabolites: pannarin (major), zeorin (major), dechloropannarin (minor), 5-7-dichloro-8-hydroxy-2-methoxy-1,3-dimethylxanthone (=TH2, minor), and 5-7-dichloro-2,8-dihydroxy-1,3-dimethylxanthone (trace). Substrate and ecology: on bark or wood of Quercus and Platanus spp., at elevations of 1280-1950 m World distribution: a southwestern North American endemic Sonoran distribution: from northern Sinaloa, through the Sierra Madre Occidental to the Santa Rita Mountains, Arizona. Notes: Rinodina perreagens is characterized by the presence of pannarin in the thallus (and sometimes the epihymenium) and is distinguished from the southern and western European R. dalmatica Zahlbr. by its lighter colored thallus, sometimes large blastidia, apothecia with more persistent thalline margins, and its larger spores. The transient polygonal lumina during the early stages of spore development is a character shared with R. isidioides and R. verruciformis, both of which lack pannarin but possess cortical atranorin, and have similar Madrean distributions.