Inverness-shire, Scotland, 2003
A lichen is a close association between a fungus and either an alga or a cyanobacterium. As lichens can grow on bare rock, which they gradually erode to form soil, they are important pioneer species.
The little black discs on this lichen are part of the fungus, and contain the spores. The algae, which can photosynthesise, are within the grey fungal mat, much of which has been stained with rust from the iron-rich rock.