[PubMed]

Xylaria hypoxylon, the type species of the fungal genus Xylaria (Xylariaceae, Sordariomycetes), was first described by Linnaeus as Clavaria hypoxylon from Sweden. Saccardo and other mycologists assumed a cosmopolitan distribution for this species. However, contradictory reports in literature on its morpho-anatomical characters and strongly inconsistent rDNA sequence data attributed to this species in GenBank suggested the existence of an unresolved species complex. To address this lack of clarity, molecular and morphological characters of numerous specimens and corresponding cultures of X. hypoxylon and related taxa from Europe were studied. Newly obtained 5.8S/ITS nrDNA sequence data were compared with published data and sequences of reference strains. Populations of X. hypoxylon from Europe exhibited rather consistent rDNA sequence data and a relatively uniform holomorphic morphology, except for one specimen from Sweden, which deviated in its ascospore morphology. DNA sequences and morphology of material from other geographic localities, however, showed substantial deviations and therefore indicated the existence of a species of its own. Some samples from Western United States showed DNA sequence data being identical to those of specimens from Europe, suggesting a North American occurrence of X. hypoxylon. Definitely not conspecific with the Swedish material examined during this study appeared to be culture material assigned to X. hypoxylon, the DNA sequence data of which have been used in various phylogenetic studies as a representative of Xylariaceae and Xylariales, respectively. This material and may represent another undescribed non-European species.