Lichens and moss

This tree has a good share of lichens - and even moss growing through the lichens.






I'm not a botanist, let alone a lichenologist, so I don't know the names, but lichens are extraordinary and beautiful things seen up close.

They're odd - composed of an alga or cyanobacterium and a fungus living together in what is probably a mutually beneficial arrangement (symbiosis). (Cyanobacteria are a special type of bacteria which can photosynthesise; they are blue-green in colour, hence cyano which means blue.) What you see is essentially the fungus, the algal cells being within it in various arrangements. The algae can generally exist on their own as well, but the fungi depend on the algae. Most lichens have one species of alga, occasionally there are two. The alga in a lichen provides photosynthesis for the fungus; in return it receives water and shelter.

There are thousands of different lichens world-wide; some inhabiting very inhospitable places. To varying degrees they are sensitive to air pollution, often failing to do well where pollution is high. They grow very slowly; some colonies may be 8 or 9000 years old.

Churchyards are important for lichens: according to the British Lichen Society, of the 1700 species in Britain, over 300 have been found on churchyard stone in lowland Britain, with many churchyards having over 100 species.