Phylum: Chlorophyta   Family: Trentepohliaceae

Trentepohlia aurea  (Linnaeus) C.F.P. Martius

An alga associated with fungal hyphae and a widespread photobiont of lichens. Naturally green, they often contain large amounts of haematochrome, an orange pigment, producing quite striking appearances at times. Commonly found on many terrestrial substrates

References: 
John, Whitton & Brook (2011) - The Freshwater Algal Flora of the British Isles