Fungi of the family Hypoxylaceae (Xylariales, Ascomycota) are ubiquitously distributed and fulfil important ecological roles as saprobes, pathogens, and endophytes. Members of this family tend to store large amounts of secondary metabolites in their carbonaceous stromatal tissue commonly formed on colonised wood. This feature is of both taxonomic and chemical value by serving as chemotaxonomic markers and sources of potential new and bioactive compounds. Despite tremendous progress in the characterisation of Hypoxylaceae both in terms of genomics and secondary metabolomics, many unknown metabolites remain to be identified or elucidated. Here, we report on the polyphasic, i.e. morphological, chemical, and genetical analysis of Hypoxylon and Annulohypoxylon spp. collected from the Iranian shore of the Caspian Sea and a chemotaxonomic study of the constituents of a concurrently studied specimen of A. michelianum. A new daldinone derivative and five new minutellin-type azaphilones from stromatal tissues of A. substygium and H. lateripigmentum, respectively, were identified in the course of this study by high-performance liquid chromatography/mass spectrometry coupling (HPLC-MS) and structurally elucidated by nuclear magnetic resonance (NMR) spectroscopy. We realised that the structure of daldinone A was misassigned and in fact equals daldinone C. Finally yet importantly, the distribution of minutellin-type azaphilones throughout the Hypoxylaceae is discussed.

During the course of our ongoing study of the diversity of Thai fungi and their secondary metabolites, numerous specimens within the Hypoxylaceae have been characterised by traditional morphology, chemotaxonomy using ultra-high-performance liquid chromatography coupled to diode array detection and ion mobility tandem mass spectrometry (UHPLC-DAD-IM-MS/MS), and molecular phylogenetic analyses. MS/MS-based analysis of the major stromatal metabolites of a newly identified taxon, Hypoxylon luteogranulatum, indicated the production of distinct compounds compared to the azaphilone and binaphthalene pigments commonly found in the Hypoxylaceae, aside from the presence of the chemotaxonomic marker binaphthalene tetrol (BNT). Further analysis suggested that one of the major metabolites had the molecular formula C₁₃H₁₃NO₃, identical to hypoxyvermelhotin A, a yellow pigment so far exclusively found in Hypoxylon lechatii. Its identity was confirmed after purification by preparative high-performance liquid chromatography with nuclear magnetic resonance (NMR) data, and genome analysis of H. lechatii revealed the presence of different hybrid polyketide synthases-non-ribosomal peptide synthetases (PKS-NRPS) hybrid clusters. Despite chemotaxonomic similarities with H. lechatii, we propose a new species, which is morphologically distinct from H. lechatii. Our molecular phylogenetic study provides substantial evidence distinguishing H. luteogranulatum clearly from H. lechatii and allied members within the Hypoxylaceae. Additionally, future studies are needed to better understand the ecological behaviour of H. luteogranulatum and identify the ecological role of the vermelhotin-like molecules within this putative interaction.

Members of the genus Hypoxylon (Ascomycota) are pleomorphic fungi mostly forming conspicuous teleomorphs, consisting of perithecia embedded into stromal tissue, and their morphology has traditionally served for species delineation. However, analysis in tandem with other phenotypic characters, such as chemical and genetic traits, proved to be a more stable predictor of interspecies and intergeneric relationships. During 2014 and 2015, a set of species identified as Hypoxylon were described from the Neotropics, exclusively relying on morphological traits. The secondary metabolite profiles of their stromata were analysed by HPLC/DAD-ESI-MS, corroborating their classification within Xylariales. Additionally, molecular data for ex-type strains of H. dussii and H. sofaiense were incorporated into an inferred molecular phylogeny of the Hypoxylaceae and allies. Furthermore, a freshly collected specimen from North Carolina was selected as epitype of Sphaeria perforata Schweinitz (syn. Hypoxylon perforatum), as its morphological/chemotaxonomic characters matched those of the holotype. Our findings demonstrate that the secondary metabolism of Hypoxylon closely correlates with both morphological features and molecular data, serving as a complement for species identification.

During the course of a screening for novel anti-infective agents from cultures of tropical Xylariaceae originating from French Guiana and Thailand, pronounced antifungal activity was noted in extracts of cultures of Hypoxylon monticulosum. A bioassay-guided fractionation led to the known metabolite sporothriolide as active principle. In addition, three new derivatives of sporothriolide were isolated, for which we propose the trivial names sporothric acid, isosporothric acid and dihydroisosporothric acid. Their chemical structures were elucidated by high-resolution electrospray mass spectrometry in conjunction with two-dimensional nuclear magnetic resonance (2D-NMR) spectroscopy. From earlier studies on the biogenesis of the chemically similar canadensolides, we postulate that the new compounds were shunt products, rather than biogenetic precursors of sporothriolide. Interestingly, this compound class, as well as strong antifungal activities, was only observed in multiple cultures of H. monticulosum, but not in several hundreds of Hypoxylon cultures studied previously or concurrently. Therefore, sporothriolide production may constitute a species-specific feature with respect to Hypoxylon and the Xylariaceae, although the compound was previously reported from non-related fungal taxa.

The introduction of a One Fungus-One Name (1F1N) concept has led to intensive discussions among taxonomists. Based on the Xylariaceae, a hyperdiverse family of Ascomycota with over 1300 species, the advantages and pitfalls of these nomenclatural changes and their consequences for taxonomy and applied mycology are discussed. Historically, in the Xylariaceae, an 1F1N concept had already been realised: the types of all important genera are conserved. Most teleomorphs were discovered long before the anamorphic states and the latter did not receive separate names, hence no drastic taxonomic changes are expected. The new nomenclature calls for abandonment of some ill-defined anamorph genera, such as Muscodor. Other anamorph genera will be retained because their names refer to morphological symplesiomorphies that occur in several teleomorph genera. Various important taxa are only known from ancient specimens, and no DNA-based data are available. Much work still remains to be done to recollect these fungi, select epitypes, and settle their phylogenetic relationships. Until then, we recommend that taxonomic changes be applied at the suprageneric ranks whenever possible to maintain nomenclatural stability.