Phylogenetic relationships among Daldinia, Entonaema, and Hypoxylon as inferred from ITS nrDNA analyses of Xylariales
Triebel, Dagmar; Peršoh, Derek; Wollweber, Hartmund; Stadler, Marc
The present molecular study focuses on the phylogenetic position of the genera Daldinia, Entonaema, and Hypoxylon. 28 double-stranded new 5.8S/ITS nrDNA sequences of species representing these genera were obtained and aligned with all 351 publicly available Xylariales sequences. In contrast to earlier works on ITS phylogeny, the phylogenetic analysis presented here was limited to the less variable, reliably alignable parts of the ITS region. This approach resulted in a tree topology that is largely in accordance with the current classification. The tree revealed four monophyletic families, Amphisphaeriaceae, Apiosporaceae, Diatrypaceae, and Hyponectriaceae, within the Xylariales. The large family Xylariaceae, however, split into three major groups. The genera with geniculosporium-like anamorphs (e.g., Entoleuca, Kretzschmaria, Nemania, Rosellinia, Xylaria) formed one clade, while genera with nodulisporium-like conidial stages (Biscogniauxia/Camillea, and Daldinia/Entonaema/Hypoxylon, respectively) were found in two clades. Within one of these clades, Daldinia and Entonaema appeared closely related, while Hypoxylon split into several subclades along an unresolved backbone. A monophyletic origin of Hypoxylon could therefore neither be confirmed nor rejected, and Hypoxylon species cluster in several wellsupported groups, most of which are in accordance with the current classification at the species or species-group levels. Most of these groups exhibit a unique sequence of the initial base pairs of the ITS1 region. Additionally, signature sequences could be inferred. The molecular studies indicate that the widely distributed species H. fuscum is not divided into host-specific entities, but a geographic distinction should be more closely investigated. Aside from certain dubious sequences, H. fragiforme formed a monophyletic group and the sequences of H. cohaerens and H. multiforme clustered together. The phylogenetic position of H. fuscopurpureum remained unclear. The relationships among Daldinia, Entonaema and Hypoxylon are discussed with respect to morphological and chemotaxonomical characters.