O. W.  Purvis, Moore, D. M., Coppins, B. J., Hawksworth, D. L., and James, P. W., The Lichen Flora of Great Britian and Ireland. London: Natural History Museum Publications, 1992.

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

J. Walter Thomson, American Arctic Lichens II. The Microlichens. Madison: The University of Wisconsin Press., 1997.

?Index Fungorum [taxonomy information]?, 2008.