A crust-forming yellow lichen. It comprises thin and flattened granules that form a thick crust. Dull yellow apothecia may be present and these darken with age.

It has a negative reaction to K and C.

There are many yellow crust-forming lichens that are similar. Caloplaca react red to K so testing is key.

Both silica-based and calcareous rocks, concrete, tarmac and wood. Most developed on nutrient-rch substrates such as bird-perching sites.

All year round

Widespread and common in Britain.

Common in Leicestershire and Rutland.