Changing taxonomic concepts and their impact on nomenclatural stability.

Experimental techniques, which are routinely applied in yeast systematics, are currently finding recognition in a growing number of filamentous taxa. Some other biochemical markers have recently been developed in hyphomycete taxonomy. The spectrum of potential criteria now comprises characters of coenzyme-Q systems, secondary metabolites, protein electrophoresis, serology, nuclear (n) DNA/DNA reassociation, mole% G+C of DNA, protein electrophoresis, nutritional physiology and ultrastructural and karyological data. In addition, a wide range of molecular techniques is gaining rapid acceptance in evolutionary, systematic, ecological and epidemiological studies. Depending on the aim of the study, partial DNA sequencing (mainly of SS and LS ribosomal genes and their spacers, but also of other genes), PCR-ribotyping and mitochondrial (mt) DNA restriction analyses are particularly powerful; for the establishment of the taxonomic position of taxa, 5.8S ribosomal (r) rRNA sequencing and Southern blotting with conserved genes are useful. Together with renewed in-depth morphological studies and the elucidation of teleomorph connections and (syn)anamorph life cycles, these techniques provide tools for an improved understanding of the phylogeny and ecological role of the distinguished taxa. Taxa are increasingly being classified along natural lines. The resulting changes in the taxonomic system, and thereby its impact on nomenclature, may be considerable. This does not help in making taxonomy any more popular among medical mycologists. However, the significance to medical mycology of an improved taxonomic system should not be underestimated. Taxonomy is now becoming enabled to describe fungi as living entities in their natural ecological niche and thereby provides a better insight into their behaviour on the human body. We are now beginning to realize that several fungi have a narrow ecological amplitude and hence their role as aetiological agents of human disease may be well defined and characteristic for the species. The clinical significance of found taxa can thus be evaluated with more precision. Below some examples of fungal groups, in which the taxonomic concepts are subject to rapid change, are presented.