B. D.  Ryan, Nash, T. H., and Hafellner, J., ?Protoparmelia?, in Lichen Flora of the Greater Sonoran Desert Region, vol. 2, Tempe, Arizona: Lichens Unlimited, 2004, pp. 425-430.

T. H.  Nash, Ryan, B. D., Gries, C., and Bungartz, F., Lichen Flora of the Greater Sonoran Desert Region, vol. 2. Tempe, Arizona, USA: Arizona State University, 2001.