INTEGRATING PHYLOGENETIC ANALYSIS AND CLASSIFICATION IN FUNGI

The central goal of taxonomic mycology is to create classifications th at communicate understanding of fungal phylogeny. To insure that taxon omy reflects up-to-date phylogenetic hypotheses, there must be efficie nt mechanisms for translating phylogenetic trees into classifications. The current taxonomic system, which is based on the hierarchy of Linn aean ranks and the International Code of Botanical Nomenclature, is un satisfactory for this purpose. One problem with the current taxonomic system is that a large number of ranks are necessary to classify compl ex phylogenetic trees. Rank proliferation creates a tension between th e desire to name clades and the need to keep the number of ranks manag eable. In addition, ranked classifications are quite sensitive to mino r changes in tree topology, and are therefore unstable. The instabilit y of ranked tree-based classifications encourages systematists to defe r naming strongly supported clades if their internal structure or high er-level relationships are not well resolved. Thus, the current taxono mic system impedes progress toward a phylogenetic classification of fu ngi. As an alternative to the current taxonomic system, de Queiroz and Gauthier developed a system of ''phylogenetic taxonomy,'' which expli citly defines taxon names as designating clades, and which does not us e taxonomic ranks. Eliminating the concept of rank promotes nomenclatu ral stability because the names of taxa are not sensitive to changes i n their position in the tree relative to other taxa. As published fung al phylogenies grow in size and number, the problems of rank prolifera tion and nomenclatural instability caused by the current taxonomic sys tem will become more severe. Serious consideration should be given to replacing the Code with a rankless system based on phylogenetic taxono my. Although at this time there is no alternative to the Code, it is l ikely that detailed proposals for rankless codes of nomenclature will be developed in the next few years.