Phylum: Chlorophyta   Family: Trentepohliaceae

Trentepohlia umbrina (Kütz.) Bornet

Although reported as common, there are few records on NBN Atlas. It has a known association with lichens

References: 
John, D.M., Whitton, B.A. & Brook, A.J. (2011) The Freshwater Algal Flora of the British Isles