Definitions in phylogenetic taxonomy: Critique and rationale

A general rationale for the formulation and placement of taxonomic definiti ons in phylogenetic taxonomy is proposed, and commonly used terms such as " crown taxon" or "node-based definition" are more precisely defined. In the formulation of phylogenetic definitions, nested reference taxa stabilize ta xonomic content. A definitional configuration termed a node-stem triplet al so stabilizes the relationship between the trio of taxa at a branchpoint, i n the face of local change in phylogenetic relationships or addition/deleti on of taxa. Crown-total taxonomies use survivorship as a criterion for plac ement of node-stem triplets within a taxonomic hierarchy. Diversity, morpho logy, and tradition also constitute heuristic criteria for placement of nod e-stem triplets.