Relatively few lichens grow on slate which makes identification easier. Most churchyards include slate headstones so these are a good place to start.
Rhizocarpon reductum
Pale grey with numerous black fruits (apothecia) which have a pale margin and are often formed in short rows. These crusty lichens usually have a black margin (prothallus).
Porpidia tuberculosa
This lichen has a white to pale blue-grey thallus (rarely tinged orange) and can be cracked. Most have a dark margin and numerous tiny grey fruits (apothecia). The overall appearance was thought to resemble an infected lung - hence the name 'tuberculosa'.
Arctoparmelia incurva
A yellow-grey lichen with narrow, crowded lobes radiating at the margins and which are turned under at the tips and pale brown underneath. Towards the centre are many large, globose, white to yellowish soralia - resembling tiny cauliflowers.
Lecanora caesiosora
Pale green to creamy grey, usually with distinctive minute brown granules over the surface. Pale soredia form clumps up to 2mm in diameter and may spread to cover the thallus. Apothecia are rare.
Melanelixia fuliginosa
Dark green/brown to blackish brown but with green shining margins. Older parts become clothed in dense, velvety isidia (tiny reproductive columns which break off to create new lichens).
Buellia aethalea
This greyish lichen has a crusty surface that is often cracked and marked with dark spots.