Baeomyces rufus

aka Brown Beret Lichen.

The perfect visual representation of how a lichen is a mutualistic symbiosis between a fungi and a photobiont. In this case an algae.
Described as common, but new to me.
If it's not fruiting it's impossible to tell and the key difference to the only other UK species it could be easily mistaken for involves understanding its habitat.

Philosophy Friday
Anyone who stops learning is old, whether at twenty or eighty. Anyone who keeps learning is young. The greatest thing in life is to have a young mind and an old heart.