The enigmatic Mixia osmundae revisited: a systematic review including new distributional data and recent advances in its phylogeny and phylogenomics

The enigmatic basidiomycete genus Mixia includes intracellular parasites of Osmunda and Osmundastrum ferns. Here, the authors review the systematic and phylogenetic history of M. osmundae, originally known as Taphrina osmundae, and provide new data from investigations of specimens of Osmunda japonica collected in Yunnan Province, China, which we determine to be conspecific with M. osmundae. In addition, Taphrina higginsii, a parasite on fronds of Osmundastrum cinnamomeum described from Georgia, USA, was confirmed to be phenotypically identical with M. osmundae. The name T. higginsii is lectotypified with a Mix specimen. Collections examined to date document four localities for M. osmundae: Japan (Honshu and Kyushu), Taiwan (Taichung), USA (Georgia), and China (Yunnan), and host-parasite relationships with the old extant ferns Osmunda japonica and its relatives and with Osmundastrum cinnamomeum. The phylogenetic placement of M. osmundae on the fungal tree of life, its evolutionary implications, and recent advances in the phylogenomics of this fungus are briefly reviewed and discussed.