C. ciliata var. tenuis, with is very variable. The podetia are greenish grey to yellowish (usnic acid). C. ciliata var. ciliata, without usnic acid, is less frequent than var. tenuis though their distributions and habitat requirements are similar.

Determiner: 
Christine Johnson

References: 
Smith et al. editors (2009) The Lichens of Great Britain and Ireland
Dobson (2018) Lichens: an Illustrated Guide to the British and Irish Species
Ahti, Stenroos & Moberg. Editors (2013) Nordic Lichen Flora. Volume 5 Cladoniaceae