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.

I. M.  Brodo, Sharnoff, S. Duran, Laurie-Bourque, S., and Sharnoff, S., Lichens of North America. Yale University Press, 2001.

?ArtDatabanken Swedish Species Information Centre?, 2009.

J. W.  Hinds and Hinds, P. L., The Macrolichens of New England, vol. 96. China: The New York Botanical Garden Press, 2007.