The defínitions of taxon names: a reply to Stuessy

Phylogenetic nomenclature (e.g., de Queiroz & Gauthier, 1990, 1992, 1994; Camino & de Queiroz, 2000) is an alternative to the traditional system of nomenclature described in the bacteriological, botanical, and zoological codes (e.g., Sneath, 1992; Ride & al., 1999; Greater & al., 2000). The most fundamental difference between phylogenetic and traditional nomenclature concerns the manner in which taxon names are defined (de Queiroz & Gauthier, 1994; de Queiroz, 1997). Stuessy (2000), however, has questioned whether taxon names are defined at all. In his view, the three types of phylogenetic definitions that have been described• node-based, stem-based, and apomorphy-based (not crown-based, contra Stuessy)• are not definitions of names but methods or concepts for taxon circumscription that have nothing to do with nomenclature (i.e., names). Stuessy's view is incorrect; it misrepresents the function of phylogenetic definitions and fails to account for how existing taxon names are applied in new taxonomic contexts under both traditional and phylogenetic systems. Stuessy did not present any evidence to support his conclusion that phylogenetic definitions are methods for taxon circumscription rather than definitions; he simply asserted his conclusion and described his view of how taxa are named under the traditional system. According to Stuessy (p. 23), "...taxa are first circumscribed (or delimited or recognised) by some stated criteria. Taxa are then referred to categories of the modem taxonomic hierarchy Through the process of referral of a taxon to a category, it receives a name by 'christening' or 'baptism'. These names are given in the fashion we name our own children, John Smith or Jane Jones; they are not defined•they are just labels to allow for effective communication". Except for the statement that taxon names are not defined, this is a more or less accurate description of how the traditional system operates. The phylogenetic system operates similarly in some respects and differently in others. One important difference is that in the phylogenetic approach, taxa need not be referred to categories in a taxonomic hierarchy; consequently, they do not receive their names through categorical referral. Contrary to Stuessy's view, taxon names are defined in both traditional and phylogenetic systems of nomenclature (de Queiroz, 1997). In the traditional system of nomenclature, taxon names are defined in terms of types and taxonomic categories. For example, the definition of the name Asteraceae is "the taxon containing the genus Aster that is assigned to the family category". In the phylogenetic system, taxon names are defined in terms of specifiers and their common ancestry relationships. For example, a node-based phylogenetic definition of the name Asteraceae might be "the clade stemming from the most recent common ancestor of Barnadesia and Aster". Perhaps the reason Stuessy thinks that taxon names are not defined is that definitions under the traditional system are taken for