Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.
Thallus: crustose, thin, consisting of discrete verrucae, up to 0.15-0.2 mm wide, or of contiguous, irregular, rugose areoles, up to 0.4-0.6 mm wide surface: gray to dark gray-brown, dull; margin: indeterminate; prothallus: lacking; vegetative propagules: absent Apothecia: sessile, frequent, often contiguous, up to 0.4-0.7 mm in diam. disc: dark brown to black, plane to slightly convex thalline margin: prominent, concolorous with thallus, or in dark thalli usually with light gray, flaking scales of epinecral layer, c. 0.1 mm wide, entire, persistent, or becoming partially excluded; excipular ring: absent thalline exciple: 60-70(-85) µm wide laterally; cortex: 10-20 µm wide; epinecral layer: usually present, c. 5 µm wide; cortical cells: up to 3.5-8 µm wide, pigmented or not; algal cells: up to 11-18.5 µm in diam.; thalline exciple: 60-100 µm below; cortex: expanded to 15-30 µm, cellular proper exciple: hyaline, 10-20 µm wide laterally, expanding up to 20-30 µm at periphery hymenium: 100-140 µm tall, paraphyses: 2-3 µm wide, sometimes conglutinate, with apices up to 4-5.5 µm wide, moderately pigmented, forming a brown epihymenium of varying darkness; hypothecium: hyaline, (30-)50-80 µm thick asci: clavate, 60-80 x 20-25 µm, 8-spored ascospores: brown, 1-septate, ellipsoid, type A or B development, Dirinaria-type, (17.5-)22-23(-27.5) x (9-)10.5-11(-13) µm, lumina angular (Physcia-like) at first, becoming rounded but retaining thick apical walls, young spores may be inflated at septum, most spores inflated in K, mature spores sometimes submucronate, endospore wall becoming pigmented (and sometimes refractive) in overmature spores; torus: absent; walls: very lightly ornamented, ornamentation not visible in old, darkly pigmented spores Pycnidia: immersed in verrucae, ostioles hyaline; conidiophores: Type VI conidia: bacilliform, 4.5-5.5 x c. 1 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on twigs and small branches of deciduous trees and shrubs World distribution: endemic to California, distributed along the coastal ranges and Sierra Nevada Sonoran distribution: Santa Cruz Island and San Gabriel Mountains, from sea level to 1475 m. Notes: Specimens with small apothecia might be mistaken for R. laevigata that species, however, has Physcia-type spores less than 20 µm long. Its habit also may be similar to R. badiexcipula but is easily distinguished by the absence of medullary sphaerophorin crystals, the unpigmented proper exciple, smaller spores, and by the lack of a columnar lower cortex.