Optimality of phylogenetic nomenclatural procedures

Abstract

Nomenclatures resulting from the application of various procedures are viewed as communication tools whose optimality can be compared. The traditional, node-based, branch-based, apomorphy-based, and cladotypic procedures are compared based on theoretical cases. The traditional procedure collects several major drawbacks: endings related to ranks are of low information content on taxa hierarchy; with respect to procedures using uninominal species names, in case of a partly unbalanced and/or partly unresolved phylogeny, the application of the procedure results into supernumerary names; a traditional taxon name is prone to be polysemic, depending upon someone’s opinion on the rank and composition of the taxon, and upon conflicting hypotheses on the phylogenetic position of name-bearing types. Alternative systems vary in merit. Names of apomorphy-defined taxa are prone to be polysemic due to possible ambiguity in the formulation of the defining character state. The cladotypic nomenclatural procedure is similar in that respect, but a set of rules allow ambiguity to be limited. The main issue of node- and branch-based procedures is that cases of synonymy cannot be settled if the inner phylogeny of taxa cannot be resolved. Cases of irresolvable synonymy can occur under apomorphy-based and cladotypic procedures, but the problem can be circumvented by the use of taxa whose defining character state is not subject to ambiguous mapping. Node-, branch- and apomorphy-based definitions as governed by the PhyloCode can produce nonsensical statements, but this problem can be fixed by the adjunction of falsifiable assumptions in use under the cladotypic procedure. Cladotypic definitions must involve a fourth assumption formulated as ‘cladotypes belong to different species’ (cladogenesis assumption). The present contribution suggests that the cladotypic procedure outperforms all other proposed procedures, producing an optimal formal lexicon useful for naming and communicating about species and taxa.