For more on British lichens see: Dobson, F. (2000) Lichens. An illustrated guide to the British species. The Richmond Publishing Co. Ltd., Slough.
For more on threatened lichens see: Church, J.M., Coppins, B.J., Gilbert, O.L., James, P.W. & Stewart, N.F. (1996) Red Data Book of Britain and Ireland: lichens. Volume 1: Britain. The Joint Nature Conservation Committee, Peterborough.