The cyanolichen <i>Fuscopannaria frullaniae</i> is a basidiolichen in the genus <i>Acantholichen</i> ( <i>Hygrophoraceae</i> , <i>Agaricales</i> )

Abstract The crustose cyanolichen Fuscopannaria frullaniae (syn. Moelleropsis nebulosa subsp. frullaniae ) is a poorly understood taxon that occurs on mosses and liverworts, described from eastern Canada and reported from the Iberian Peninsula, Macaronesia and the eastern USA. Originally placed in the genus Moelleropsis , the position of the species has been debated in the absence of sexual fruiting structures and, until now, DNA sequences from the fungal symbiont. We produced nine sequences from two fungal ribosomal loci from F. frullaniae collected at five different localities in Nova Scotia, Canada and North Carolina, USA. Initial BLASTn queries against public databases revealed high similarity between these sequences and basidiomycete sequences from the Dictyonema clade in Hygrophoraceae , specifically from the genus Acantholichen. We did not obtain ascomycete sequences from any locus or specimen. Phylogenetic analyses recovered the obtained sequences within the broader Acantholichen clade. We conclude that the lichen fungal symbiont is in fact a basidiomycete and introduce for it the new combination Acantholichen frullaniae. Acantholichen frullaniae is the first species of the genus to possess a granular, crustose thallus. The species lacks the characteristic, spiny, balloon-shaped cells called acanthohyphidia that are found in other species of the genus, though it possesses similar, albeit spineless cells on the surface of thallus granules; we suggest that these structures within the wider genus are homologous and represent spiny or smooth cystidia. Numerous samples yielded evidence of basidiospores and basidia produced from thallus granules, evident only after treatment with diluted potassium hydroxide, representing the first sexual structures reported in the genus. We discuss the possible reasons for this, as well as the ecology and threats to the species across its Canadian populations.