These are terribly exciting organisms consisting of two different life forms living symbiotically. One part is a fungus called a mycobiont and the other is a photobiont which is either a green alga or a cyanobacterium. The fungus provides the structure while the photobiont provides the food through photosynthesis. Neither can live without the other. There are four main structural forms; crustose, squamulose, foliose and fruticose. Aren’t those great names? There is much more detailed information here.
Lichens are very fragile and susceptible to pollution, they tend not to re-establish themselves easily. So if you have lichen, look after it.
They can be found in almost any environment on earth; desert, tundra, rainforest and they will grow on trees, on rock and famously adorn old gravestones.
So are we all liking the lichen now?