A very thin, grey to brown thallus, lacking soredia. The black apothecia may be lirellate, small, rounded or ellipsoid to elongate, sinuous or sometimes branched or stellate. A widespread and common species across the UK, but first recorded in the Outer Hebrides in 2019. Prefers sheltered sites on smooth-barked hosts

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