Large, smooth and lustrous thallus, grey to red-brown with buff undersurface and yellow medulla yellow. The red-brown apothecia, are produced from the lobe under-surfaces and are partially hidden by the lobe margins.On deciduous trees in established woodlands and parks. Common but biased towards the north-west

References: 
Ahti et al. editors (2012) Nordic Lichen Flora, Volume 3: Cyanolichens
Smith, C.W. et al. editors (2009) The Lichens of Great Britain and Irelandd