Dog lichen

From looking at lichens on tree branches a week ago, today I was finding lichens along the trackway of a disused railway line. This Peltigera species is quite prolific on the moss-covered ballast along one section of the line. I'm fairly sure it is Peltigera didactyla. This whole group of foliose lichens is referred to as the dog lichens, after structures that are particularly well developed in Peltigera canina and look like dogs' teeth.