Acremonium is acknowledged as a highly ubiquitous genus including saprobic, parasitic, or endophytic fungi that inhabit a variety of environments. Species of this genus are extensively exploited in industrial, commercial, pharmaceutical, and biocontrol applications, and proved to be a rich source of novel and bioactive secondary metabolites. Acremonium has been recognised as a taxonomically difficult group of ascomycetes, due to the reduced and high plasticity of morphological characters, wide ecological distribution and substrate range. Recent advances in molecular phylogenies, revealed that Acremonium is highly polyphyletic and members of Acremonium s. lat. belong to at least three distinct orders of Sordariomycetes, of which numerous orders, families and genera with acremonium-like morphs remain undefined. To infer the phylogenetic relationships and establish a natural classification for acremonium-like taxa, systematic analyses were conducted based on a large number of cultures with a global distribution and varied substrates. A total of 633 cultures with acremonium-like morphology, including 261 ex-type cultures from 89 countries and a variety of substrates including soil, plants, fungi, humans, insects, air, and water were examined. An overview phylogenetic tree based on three loci (ITS, LSU, rpb2) was generated to delimit the orders and families. Separate trees based on a combined analysis of four loci (ITS, LSU, rpb2, tef-1α) were used to delimit species at generic and family levels. Combined with the morphological features, host associations and ecological analyses, acremonium-like species evaluated in the present study are currently assigned to 63 genera, and 14 families in Cephalothecales, Glomerellales and Hypocreales, mainly in the families Bionectriaceae, Plectosphaerellaceae and Sarocladiaceae and five new hypocrealean families, namely Chrysonectriaceae, Neoacremoniaceae, Nothoacremoniaceae, Pseudoniessliaceae and Valsonectriaceae. Among them, 17 new genera and 63 new combinations are proposed, with descriptions of 65 new species. Furthermore, one epitype and one neotype are designated to stabilise the taxonomy and use of older names. Results of this study demonstrated that most species of Acremonium s. lat. grouped in genera of Bionectriaceae, including the type A. alternatum. A phylogenetic backbone tree is provided for Bionectriaceae, in which 183 species are recognised and 39 well-supported genera are resolved, including 10 new genera. Additionally, rpb2 and tef-1α are proposed as potential DNA barcodes for the identification of taxa in Bionectriaceae.
