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.

T. D. V.  Swinscow and Krog, H., Macrolichens of East Africa. Dorchester: Henry Ling Ltd, The Dorset Press, 1988.

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