Lichens on Apple Trees

I have been pruning our old apple trees and looking at the lichens on the twigs from the top of one of the trees.  This one has three species: Xanthoria parietina (the yellow one), Ramalina farinaceae, (the feathery one) and Physcomia distorta, (the grey one).  Another twig had Flavoparmelia caperata.   Many of the older twigs are quite encrusted with lichens and I am going to be examining them to see how many species I can identify over the next few weeks as I get on with the winter pruning.  My enthusiasm for this project has been fired by the Natural History Museum's 'lichens on twigs key' on its website.  I must admit to finding lichens a difficult group and the keys in Dobson's guide are not the easiest to work with, especially if you do not have the chemicals and a high power microscope.  But this was a doddle and I would recommend anyone to give it a try.