18S Ribosomal DNA Sequence Data and Dating, Classifying, and Ranking the Fungi
How could information from 18S ribosomal DNA sequences be incorporated into a classification system? Molecular systematic studies are yielding a wealth of new fungal taxonomic characters. In some cases, DNA sequence data support traditional taxonomic groups. In other cases, among ascomycetous yeasts for example, sequence data suggest new, unfamiliar groupings that require revision of the classification. Whether from molecular or traditional approaches, increased resolution of taxonomic relationships is leading to situations in which the number of ranks available for classification is inadequate for complete description of relationships. Possible solutions to the problem of proliferating ranks include accepting paraphyletic groups or eliminating the traditional ranks like family, class, order, and so on. Hennig proposed that taxa that diverged at about the same geological time should be given the same ranking. With a combination of evidence from sequence data and from the fossil record, we have estimated the timing of some fungal divergences, and we explore the consequences of basing rankings on geological age of origins.
KeywordsMonophyletic Group Neurospora Crassa Ascomycetous Yeast Filamentous Ascomycete Paraphyletic Group
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