Phylum: Ascomycota Family: Hysteriaceae
Hysterium angustatum Alb. & Schwein.
Widespread but infrequently reported. Found on many deciduous tree species. Similar to Hysterium pulicare but that species has spores with paler end-cells and generally longer spores (but with some overlap)
Boehm (2013) Home of the Hysteriaceae, Mytilinidiaceae & Gloniaceae - Website: Fungi and Lichens of Great Britain and Ireland