What is the difference between nomenclature and taxonomy?

Nomenclature is the system of scientific names for taxa (such as species, genera, or families) and the rules and conventions for the formation, treatment, and use of those names. It follows an internationally agreed, quasi-legal procedure. Taxonomy is the identification and interpretation of natural groups of organisms (i.e., taxa) based on characters (such as morphology, genetics, behaviour, ecology). The discovery and delimitation of taxa is a science. Nomenclature and taxonomy are closely allied, but separate aspects ordering information about biodiversity. They overlap in the definition of type specimens, which tie the name to a single physical standard.

Further explanation excerpted from Pyle & Michel (2008) ZooBank: Developing a nomenclatural tool for unifying 250 years of biological information. Zootaxa 1950: 39–50 (2008), {available here: http://www.mapress.com/zootaxa/list/2008/zt01950.html}.

Taxonomy, nomenclature and typification

Taxonomy and nomenclature are closely allied, but separate and complementary endeavours in developing the language of biodiversity. Discovering and delimiting species is the challenging job of alpha taxonomy; determining relationships and establishing higher taxa is referred to as beta taxonomy. Delimiting both alpha and beta taxa requires using a range of character data to test hypotheses about the inclusiveness of taxon definitions. This can naturally lead to strongly opposing alternative points of view, depending on character selection, method of analysis, and philosophical stance of the taxonomist. Definitions of taxa, from species to genera to higher taxa, can thus change significantly as the iterative process of improving the tests of taxonomic boundaries weighs alternative hypotheses and moves to new conclusions. Although it may be a source of frustration to end-users who simply want defined taxonomic entities, this process of change is a sign of the health of the science of taxonomy. Ultimately, if data accumulation were to saturate and if philosophical perspectives on species definitions were to converge, it is possible that taxonomy would stabilize and reach consensus definitions for taxa (changing only to accommodate ongoing organismal evolution). This situation is not on the foreseeable horizon.

By contrast, the establishment of scientific names of animals is not a scientific process of testing alternatives; rather, it involves a bibliographic and quasi-legal process of presentation of a name with appropriate supporting documentation in a publication. Although a scientific name is generally established within the context of a published work on taxonomy, its link to actual organisms is through the primary type specimen (or specimens). This process of typification allows the name to be tied to a physical standard (and hence provides an objective basis for identifications), but leaves room for taxonomy to change; different names can be applied to taxa as is appropriate for their new boundaries. Figure 1 presents a tree-based example, in which alternative interpretations by different taxonomists result in different generic groupings, each of which could take a different name depending on the type species of the generic group. The same process could be visualized simply based on variation, with a more inclusive (‘lumping’) perspective requiring one type specimen for a species, thus receiving one name; whereas a more divisive (‘splitting’) perspective requires names derived from several type specimens for the perceived groups. Choosing between available names for types in a group is generally governed by the Principle of Priority, such that name first established should be used for that group (Figure 1). However, even if names are not in current use for a group, if they were originally validly published they are not permanently retired, as they may well be needed in the future. Taxonomic work may split an existing group, because less inclusive taxa are more consistent with data in hand. Having older names ready to apply provides an immediate tool for recovering past information on that taxon.

We want to underscore that the work of nomenclature aims for stability in names, but is completely independent of the process of flexibility in taxonomic interpretation. This philosophy is fundamental to the ICZN’s role, as articulated in the Introduction to the 4th Edition of the ICZN Code which states:

“There are certain underlying principles upon which the Code is based. These are as follows:

  1. The Code refrains from infringing upon taxonomic judgment, which must not be made subject to regulation or restraint.
  2. Nomenclature does not determine the inclusiveness or exclusiveness of any taxon, nor the rank to be accorded to any assemblage of animals, but rather provides the name that is to be used for a taxon whatever taxonomic limits and rank are given to it.
  3. The device of name-bearing types allows names to be applied to taxa without infringing upon taxonomic judgment. [etc] ” (ICZN p. xix).”

A cartoon graphic for the relationship of the trinity of nomenclature, taxonomy and type specimens is shown in Figure 2.

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith