A Comparison of Phylogenetic Nomenclature with the Current System: A Botanical Case Study

Abstract

The family Lamiaceae was used as a case study to compare our current system of nomenclature with a phylogenetic alternative proposed by de Queiroz and Gauthier (1992, Annu. Rev. Ecol. Syst. 23:449–480), with emphasis on nomenclatural stability and efficiency. Comparison of published cladistic analyses revealed 19 suprageneric clades within Lamiaceae that are supported well enough to merit naming, but many genera could not be placed with confidence in any infrafamilial taxon. Two phylogenetic classifications were prepared, one following current nomenclatural rules and conventions and the other following the phylogenetic system of nomenclature. A comparison of the classifications revealed examples of unstable and ambiguous names that resulted from employing current rules and conventions to name clades. Old names based on nomenclatural types of uncertain phylogenetic relationship and infrafamilial taxon names based on the type of the family are particularly prone to instability. The phylogenetic system appears to have fewer problems but may also lead to nomenclatural confusion if taxon names are defined carelessly. The current system produces less efficient classifications because the principle of exhaustive subsidiary taxa leads to inclusion of redundant names (monotypic taxa) when the classification is based on an asymmetrical cladogram. In contrast, the phylogenetic system contains no redundant names. We endorse the recommendation that the principle of exhaustive subsidiary taxa be abandoned. Phylogenetic definitions should be provided for taxon names whenever phylogenies are translated into classifications. The definitions should be accompanied by a list of synapomorphies and a statement of clade membership to facilitate subsequent provisional referral of newly studied species to supraspecific taxa.