Phylum: Ascomycota Family: Taphrinaceae
Taphrina alni (Berk. & Broome) Gjaerum
Alder Tongue
A plant pathogen that causes a tongue-like gall, hence the common name. Rather common
References:
Ellis & Ellis (1997) - Microfungi on Land Plants
Redfern & Shirley (2011) - British Plant Galls