Chewing Gum Lichen – Lecanora muralis

Usually forms a loose rosette and has a variety of colours from off white, through dirty greys to pale browns.

Found on natural, bird-enriched rocks, and on concrete and other urban substrates; widespread and becoming very common in urban areas, less so in the north and west. When seen on paving slabs it is often assumed to be discarded and trodden chewing gum