Phylum: Ascomycota Family: Phaeospaeriaceae
Amarenomyces ammophilae (Lasch) O.E. Erikss.
A very common fungus on the dead stems and leaves of marram grass (Ammophila arenaria)
References:
Ellis & Ellis (1997 new enlarged edition) Microfungi on Land Plants: An Identification Handbook
Dennis (1981) Fungi of Ammophila arenaria in Europe