Xenasmatellales ord. nov. and Xenasmatellaceae fam. nov. for Xenasmatella (Agaricomycetes, Basidiomycota).

In the era of molecular phylogeny as dominant evidence in fungal taxonomy, the taxonomic framework of fungi adopted from morphological characteristics has been largely updated. Compared with other fungal groups, macrofungi underwent fewer updates at the order and higher level. In this study, the taxonomic placement of a poorly known macro-basidiomycetous genus Xenasmatella is studied. Phylogenetic and molecular clock analyses inferred from a seven-locus dataset support that the genus represents an order rank lineage. Accordingly, a monotypic order Xenasmatellales and a monotypic family Xenasmatellaceae are newly introduced for Xenasmatella within Agaricomycetes. The species diversity and relationships of Xenasmatella are further clarified with the aid of the phylogenetic analysis inferred from a four-locus dataset. In association with morphological characteristics, a new species Xenasmatella hjortstamii is described. Moreover, the distribution of Xenasmatella ailaoshanensis, X. gossypina, and X. wuliangshanensis previously known only from type localities in Yunnan Province, China are expanded. In addition, two unnamed single-specimen lineages of Xenasmatella from Victoria State, Australia and Sichuan, China are revealed, likely representing two potential new species of this genus. In summary, the current study updates the taxonomic framework of Agaricomycetes and provides a crucial supplement for comprehensively understanding the evolutionary history of this fungal class.