Lepraria incana (L.) Ach.
Thin powdery, grey-blue indistinct thallus found on shaded acid rocks and trees. Common and regarded as a species complex
Smith, C.W. et al. editors (2009) The Lichens of Great Britain and Irelandd
Dobson, F.S. (2018) Lichens: an Illustrated Guide to the British and Irish Species