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, comprised of small discrete, plane to convex areoles, up to c. 0.2 mm wide, sometimes becoming contiguous, plane to rugose surface: light gray-brown to dark copper-brown, dull; margin: determinate or not; prothallus: lacking; vegetative propagules: absent Apothecia: frequent, widely dispersed and sessile, or contiguous and adnate, up to 0.3-0.6 mm in diam. disc: dark brown, usually becoming black, plane to slightly convex thalline margin: concolorous with thallus, 0.05-0.1 mm wide, entire or somewhat flexuose, persistent; excipular ring: absent thalline exciple: 50-65 µm wide laterally; cortex: 5-10 µm wide; cells: up to 4.5-6 µm wide, pigmented; algal cells: up to 8.5-11 µm in diam.; thalline exciple: 50-80 µm thick below; cortex: sometimes expanded, c. 20 µm, cellular proper exciple: hyaline, 5-10 µm wide laterally, expanded to 10-20 µm wide at periphery hymenium: 60-80 µm tall; paraphyses: 1.5-2.5 µm wide, not conglutinate, with apices up to 3.5-5.5 µm wide, lightly or heavily pigmented, immersed in dispersed pigment, forming a red-brown epihymenium; hypothecium: hyaline, 40-90 µm thick asci: clavate, 40-60 x 14-17 µm, 8-spored ascospores: brown, 1-septate, broadly ellipsoid, type A development, Pachysporaria-type, (12.5-)15-16(-18.5) x (7-)8.5-9(-10) µm, lumina irregularly angular prior to wall pigmentation (Physcia-like), becoming irregularly rounded, walls remaining thick; torus: dark at maturity; walls: not ornamented (Fig. 63); pigmented, single celled spores common in some specimens, with apical thickenings (as in type B development) Pycnidia: immersed in thallus; conidiophores: Type I conidia: c. 4.5 x 1 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on twigs and smooth bark of both coniferous and deciduous trees; a pioneer species sometimes associated with R. boulderensis World distribution: a western North American endemic restricted to drier areas in the Black Hills and southern Rocky Mountains Sonoran distribution: frequent in Arizona, south into Chihuahua, at elevations of 1900-3050 Notes: The Pachysporaria-type spores of R. coloradiana make this species difficult to confuse with other montane western species on bark or wood. Forms with scattered apothecia and dispersed areoles are superficially similar to R. septentrionalis Malme, a boreal species that does not occur in the study area. Apothecia of both species are sessile and develop a slightly expanded lower cortex but R. coloradiana is distinguished by its Pachysporaria-, rather than Physcia-type spores. Sonoran collections of R. glauca may also have a similar habit and thallus pigmentation but this species differs in possessing Physcia-type, although similar sized spores with a prominent torus.