Resembles P. membranacea but with much flatter veins and dense, bushy rhizines on the underside. Distribution restricted to basic coastal grassland and dunes

References: 
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
Ahlti et al. editors (2012) Noric Lichen Flora. Volume 3: Cyanolichens