Whitish grey thallus with indistinct aureoles (islands). Sunken dark apothecia are usually present, often two per aureole.

K+ yellow-orange

C. contorta has more circular and separated aureoles.

On soft limestones and becoming very common on concrete, on cement and even tarmac in urban areas.

All year round.

Widespread and increasingly common in Britain.

Fairly frequent in Leicestershire and Rutland.