Rust-coloured, areolate, crustose thallus with black prothallus. Numerous immersed apothecia, concave, with raised margins. On exposed, hard, siliceous rocks, mainly in upland areas

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