Characterized by the arching, dorsiventral stems, with flattened, deeply divided phyllocladia. A close examination of the structure is required in this often difficult genus. Size and number of septa in the spores is useful but much data are missing, often due to a lack of apothecia. Common in the north-west on siliceous rocks

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