Phylogenetic relationships vs. phenotypic diversity: how to achieve a phylogenetic classification system of the...

To establish a hierarchic classification system, ranks cannot be defined by the exclusive and inflexible application of phylogenetic parameters. Because both stability and practicality are prerequisites for a successful system, decisions about the delineation of genera must be made by combining phylogenetic coherency with unifying phenotypic properties of taxonomic value consistent with the needs of a hierarchic system. The phylogenetic depth (age) of a genus has no influence on the decision as long as the members of the genus can be reliably identified as such. The description of those higher taxa that are not easily definable today because of the lack of common phenotypic properties must be postponed until new insights are available. In the end this approach will be both phylogenetic and practical, thus avoiding the use of two classification systems.