<i>Xenasmatellales</i> ord. nov. and <i>Xenasmatellaceae</i> fam. nov. for <i>Xenasmatella</i> (<i>Agaricomycetes, Basidiomycota</i>)

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 <i>Xenasmatella</i> 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 <i>Xenasmatellales</i> and a monotypic family <i>Xenasmatellaceae</i> are newly introduced for <i>Xenasmatella</i> within <i>Agaricomycetes</i>. The species diversity and relationships of <i>Xenasmatella</i> are further clarified with the aid of the phylogenetic analysis inferred from a four-locus dataset. In association with morphological characteristics, a new species <i>Xenasmatella hjortstamii</i> is described. Moreover, the distribution of <i>Xenasmatella ailaoshanensis, X. gossypina</i>, and <i>X. wuliangshanensis</i> previously known only from type localities in Yunnan Province, China are expanded. In addition, two unnamed single-specimen lineages of <i>Xenasmatella</i> 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 <i>Agaricomycetes</i> and provides a crucial supplement for comprehensively understanding the evolutionary history of this fungal class.