The genus Thyridium, previously known as a saprobic or hemibiotrophic ascomycete on various plants, was revised taxonomically and phylogenetically. Sequences of the following six regions, that is, the nuclear ribosomal internal transcribed spacer (ITS) region, the large subunit (LSU) of rDNA, the second largest RNA polymerase II subunit (rpb2) gene, translation elongation factor 1-alpha (tef1) gene, the actin (act) gene, and the beta-tubulin (tub2) gene, were generated for molecular phylogenetic analyses of species of this genus. Phialemoniopsis, a genus encompassing medically important species, is synonymised with Thyridium based on molecular evidence and morphological similarities in their asexual characters. The generic concept for Thyridium is expanded to include species possessing both coelomycetous and hyphomycetous complex asexual morphs. In addition to type species of Thyridium, T. vestitum, nine species were accepted in Thyridium upon morphological comparison and molecular phylogenetic analyses in this study. All seven species of Phialemoniopsis were treated as members of the genus Thyridium and new combinations were proposed. A bambusicolous fungus, Pleospora punctulata, was transferred to Thyridium, and an epitype is designated for this species. A new species, T. flavostromatum, was described from Phyllostachys pubescens. The family Phialemoniopsidaceae, proposed as a familial placement for Phialemoniopsis, was regarded as a synonym of Thyridiaceae. A new order, Thyridiales, was established to accommodate Thyridiaceae; it forms a well-supported, monophyletic clade in Sordariomycetes.
