Most of the lichens I have started with are those on trees, my thinking being that they may be specific to particular species, though of course this is not always strictly true. Nevertheless, this has helped me to focus a little.
The first one I pinned down was this abundant yellow/orange lichen which seems to be everywhere. This is the Common Orange Lichen (Xanthora parietina). The name is derived from the yellow pigment xanthorin, which is thought to be produced as a defence against UV radiation, to which it is susceptible if it grows in exposed areas.
|Common Orange Lichen (Xanthora parietina)|
Another seemingly abundant species it the Oakmoss (Evernia prunastri), which is another common lichen of twigs. This is not just found on oak species, it is also on hawthorn (where this example is photographed). This species has grey/green branches which are typically whitish underneath, and once you start looking it can be found everywhere.
|Oakmoss (Evernia prunastri)|
Another species which I have found across my 1km square is Hammered Shield Lichen (Parmelia sulcata). This silvery grey/green lichen has dish-like lobes. These have an uneven surface, with depressions and pimples which give the species a hammered appearance. Perhaps similar to how Father Ted tried to even out the dent in the car.
|Hammered Shield Lichen (Parmelia sulcata)|