Immersed, pale grey to whitish thallus with black apothecia, variable in shape but usually irregularly stellate. Found on nutrient rich smooth bark and twigs, often on Ash (Fraxinus excelsior)

References: 
Smith, C.W. et al. editors (2009) The Lichens of Great Britain and Irelandd
Dobson, F.S. (2018) Lichens: an Illustrated Guide to the British and Irish Species