Xylographa vitiligo

Xylographa vitiligo is a species of wood- and bark-dwelling lichen in the family Xylographaceae. This European lichen typically grows on the wood of fallen trees and stumps, occasionally colonising the bark of coniferous species, and is found primarily in northern latitudes and mountainous regions. The species has a complex taxonomic history due to confusion in the original specimens, which required later designation of a lectotype to clarify the name's application....read more on Wikipedia.