Phylum: Ascomycota Family: Verrucariaceae
Muellerella lichenicola (Sommerf.) D. Hawksw.
Widespread but biased towards the south-east of Britain. A lichenicolous fungus recorded on a number of lichen genera including Caloplaca, Lecanora, Mycobilimbia
References:
Smith, et al., editors (2009) - The Lichens of Great Britain and Ireland