In traditional nomenclature, outlined in the bacteriological, botanical, and zoological codes of nomenclature, taxa have descriptions and circumscriptions while their names have types and ranks. Recently, K. De Queiroz and J. Gauthier have developed a phylogenetic alternative in which formal ranks are abandoned and names of taxa are provided with verbal definitions based on descent. Under such a system, there is greater nomenclatural stability in that a taxon’s name does not change with a change in the taxon’s hierarchical placement. However, this can result in the lack of uniformity among terminations (for uninomials) and forenames (for binomials) at a given hierarchical level. Phylogenetic definitions would increase explicitness and universality regarding the application of names by establishing a one-clade, one-name system. However, such a system, may lack practicality as intensional and extensional connotations frequently associated with a name could not be taken into consideration when applying the name once it is defined. Also, phylogenetic definitions attach additional elements beyond the type to the taxon name and this can result in a reduction in taxonomic flexibility and circumscriptional stability. Adoption of a phylogenetic nomenclature is probably best done through the modification of the current codes of nomenclature to permit (but not require) the valid publication of unranked names and the development of a supplementary code of phylogenetic nomenclature that governs the nomenclature of such names. Such a supplemental code should buffer against the drawbacks to phylogenetic nomenclature by allowing a mechanism by which a phylogenetic definition could be altered to prevent dramatic shifts in the taxon’s circumscription. Such a code will also have to address numerous nitty-gritty nomenclatural issues including: typification, priority assignment to binomials, a starting point for priority, use of names originally established under the current codes of nomenclature, valid publication, and legitimacy.

Key words: nomenclature, phylogenetic, taxon, type