Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.
Thallus: fruticose, shrubby or tufted to rarely subpendulous, up to 7(-13) cm long branching: moderately branched, growing from a narrow holdfast branches: solid, flattened to weakly canaliculate, up to 3(-5) mm wide surface: greenish yellow, entire, without soredia pseudocyphellae: common, laminal or marginal, ellipsoid, semi-globose or protruding cortex: distinct, 15-20 µm thick; chondroid strands: continuous, weakly to conspicuously cracked Apothecia: common, laminal or subterminal, entire disc: concave, white pruinose, without white margins; margin: concolorous with the thallus, entire or dissected, rarely with pseudocyphellae asci: elongate-clavate, 8spored ascospores: hyaline, 1-septate, broadly fusiform, 14-16 x 5-6 µm Pycnidia: not observed Spot tests: cortex K-, C-, KC+ yellow, P-; medulla K-, C-, KC-, P- Secondary metabolites: cortex with usnic acid (major); medulla with (Race 1) 2'-O-methylstenosporic acid (major) and 2'-O-methyldivaricatic (minor), (Race 2) divaricatic acid (major) and 4'-O-demethyldivaricatic (minor), (Race 3) boninic acid (major), and 2'-O-methylsekikaic and 2'-O-methylpaludosic acids (both minor). Substrate and ecology: on twigs, especially on Quercus spp., in mountain regions, elevation higher than 1000 m World distribution: endemic to Mexico (Coahuila, Durango, Hidalgo, México, Puebla and the southern Sonoran region) Sonoran distribution: Baja California Sur, Chihuahua, Sinaloa and Sonora. Notes: Three chemical races are found in Ramalina quercicola as shown above. However, no morphological differences among them were observed. Ramalina quercicola closely resembles R. subfraxinea, a species widely distributed in lowland, in subtropical and tropical regions in the Pacific, that differs in having flat to +depressed pseudocyphellae and by its disc with a white margin that splits proper and margins. Ramalina quercicola is endemic to Mexico where it is primarily restricted on bark of Quercus in mountainous regions.