Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.
Thallus: crustose, thick, areolate, areoles convex and lobate at periphery of thallus, up to 1.2-1.6 mm wide surface: brown, more rarely ochraceous or dark gray, dull or shiny, light colored thalli usually fertile; margin: usually indeterminate; prothallus: sometimes visible on hard substrates, pale, fimbriate soredia: often developing on upturned areole margins in darker thalli lacking apothecia Apothecia: absent when sorediate, or adnate, frequent and often contiguous, up to (0.35-)0.5-1.1 mm in diam. disc: black, persistently plane, sometimes becoming fissured thalline margin: concolorous with thallus, c. 0.1 mm wide, entire and persistent; excipular ring: absent thalline exciple: 90-160 µm wide laterally; cortex: 10-20 µm wide; epinecral layer: 5-10 µm thick; cortical cells: up to 4.5-6.5 µm wide, pigmented or not; algal cells: up to 10.5-13 µm in diam. proper exciple: hyaline, 10-20 µm wide, expanding to 40-50 µm at periphery hymenium: 120-140 µm tall; paraphyses: 2-2.5 µm, not conglutinate, wide with apices up to 3.5-4.5 µm wide, lightly pigmented, immersed in blue pigment, forming a blue-gray epihymenium, K+, N+ rose or violet; hypothecium: hyaline, 120-190 µm thick, including stipe asci: clavate, 50-90 x 16-20 µm, 8-spored ascospores: brown, 1-septate, broadly ellipsoid, developmental type A, Bicincta-type, (15.5-)18.5-20.5(23.5) x (9.5-)11-12.5(-14) µm, pigmentation sometimes commencing at single cell stage, broad canal only visible in minority of immature spores, lumina mostly rounded, lateral wall expanded at septum when young, more so in K, spores later becoming waisted, septum strongly pigmented at maturity, cells lacking pigmented bands; torus: absent; walls: not ornamented Pycnidia: not seen Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on limestone, sandstone and shale, at elevations of 760-3170 m, often associated with intermittent water seepage, often collected with R. castanomela World distribution: southern Europe and central Asia, and southwestern North America, especially on the Colorado Plateau Sonoran distribution: Arizona, Coconino and Navajo Counties. Notes: North American material lacks an inspersed hymenium and would be referred to R. violascens H. Magn. by Mayrhofer (1984), who further distinguishes R. zwackhiana and R. violascens on the basis of their Dubyana- and Buellia-type spores, respectively. Spore structure is extremely variable, depending on developmental stage, and in the opinion of this author the two species are not separable by spore type. Mayrhofer (loc. cit.) shows the spores of R. violascens with swelling at the septum and separation of wall layers in both the septal and apical regions. Sheard (1982) illustrates similar spore features for R. zwackhiana, with the exception that separate wall layers at the apices have not been observed. The spores are best interpreted as belonging to the Bicincta-type but lacking the usually characteristic pigmented bands around each cell. Other species with Bicincta-type spores, such as R. castanomela and R. constrictula, show very poor development of these bands and their presence therefore should not be regarded as definitive for the spore type.