The validity of reclassifying filamentous, ascomycetous anamorphs solely on the basis of ribosomal DNA sequences is examined. We suggest that emotional reactions to the debate are a consequence of often unacknowledged philosophical biases. From the perspective of the scientific method, neither morphological nor sequence-based taxonomic studies are inherently superior. A review of published information on the internal transcribed spacer of filamentous Ascomycetes and ascomycetous anamorphs demonstrates that uniform species concepts based on DNA sequences alone are presently infeasible. Because a phylogenetic scheme should classify species, the concept that fungi can be typified or classified solely by DNA sequences is challenged. Similarly, because no adequate nonmorphological species concept exists for anamorphic fungi that lack a sexual state, integration of the Deuteromycetes into the holomorphic classification on the basis of DNA sequences alone is also presently impractical. Key words: DNA sequencing, fungal taxonomy, internal transcribed spacer, species concepts.
