Parmelia saxatilis s. lat. Grey Crottle

A pale grey, foliose lichen which has a network of white lines on its thallus and an undersurface which is black and covered with rhizines. Grey-brown isidia are often abundant on the surface of the older parts of the thallus. It is a common lichen which grows on trees, preferring acidic bark, wooden posts, boulders and dry stone walls, particularly in upland areas. It is quite tolerant of sulphur dioxide pollution.

Listed by Alan Orange in Flora of Glamorgan (Wade et al, 1994).