Very variable, hair-like, fruticose, pendant, thallus, pale to dark smoky-brown. Often with a pale base. Soralia fissure-like as well as tubercule-like. On acid-barked trees, siliceous rocks, amongst mosses, on walls and worked timber

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
Thell & Moberg, editors (2011) Nordic Lichen Flora, Volume 4: Parmeliaceae