O.  Gilbert, Lichens. London: HarperCollins, 2000, p. 288.

T. H.  Nash_, III, Ryan, B. D., Gries, C., and Bungartz, F., Lichen Flora of the Greater Sonoran Desert Region, vol. 1. Tempe: Lichens Unlimited, 2001.

?Index Fungorum [taxonomy information]?, 2008.

T.  H. Lumbsch and Huhndorf, S. M., ?Outline of Ascomycota - 2007. [Classification Information]?, Myconet, vol. 13, pp. 1-58, 2007.