Tremella cetrariellae (Tremellales, Basidiomycota, Fungi), a new lichenicolous fungus on Cetrariella delisei

Tremella cetrariicola is shown to be heterogeneous and to represent two phylogenetic sister species, which are shown here to be distinct in the morphology of the galls, basidia and basidiospores, and in their host selection. Tremella cetrariicola s. str. is confined to Tuckermannopsis, whilst the material on Cetrariella delisei is described here as the new Tremella cetrariellae. The new species is known from Finland, Greenland, Norway, Russia, Svalbard, and Sweden.