Botanical Nomenclature - Relationship To Taxonomy

Relationship To Taxonomy

Botanical nomenclature is closely linked to plant taxonomy, and botanical nomenclature serves plant taxonomy, but nevertheless botanical nomenclature is separate from plant taxonomy. Botanical nomenclature is merely the body of rules prescribing which name applies to that taxon (see correct name) and if a new name may (or must) be coined.

Plant taxonomy is an empirical science, a science that determines what constitutes a particular taxon (taxonomic grouping, plural: taxa): e.g. "What plants belong to this species?" and "What species belong to this genus?". The definition of the limits of a taxon is called its 'circumscription'. For a particular taxon, if two taxonomists agree exactly on its circumscription, rank and position (i.e. the higher rank in which it is included) then there is only one name which can apply under the ICN. Where they differ in opinion on any of these issues, one and the same plant may be placed in taxa with different names. As an example, consider Siehe's Glory-of-the-Snow, Chionodoxa siehei:

• Taxonomists can disagree as to whether two groups of plants are sufficiently distinct to be put into one species or not. Thus Chionodoxa siehei and Chionodoxa forbesii have been treated as a single species by some taxonomists or as two species by others. If treated as one species, the earlier published name must be used, so plants previously called Chionodoxa siehei become Chionodoxa forbesii.

• Taxonomists can disagree as to whether two genera are sufficiently distinct to be kept separate or not. While agreeing that the genus Chionodoxa is closely related to the genus Scilla, nevertheless the bulb specialist Brian Mathew considers that their differences warrant maintaining separate genera. Others disagree, in which case they will call Chionodoxa siehei, for example, Scilla siehei. The earliest published genus name must be used when genera are merged; in this case Scilla predates Chionodoxa.

• Taxonomists can disagree as to the limits of families. When the Angiosperm Phylogeny Group (APG) first published its classification of the flowering plants in 1998, Chionodoxa siehei would have been placed in the family Hyacinthaceae, which was one of the families which was then recognized. In the 2009 revision of their classification, the APG no longer recognize the Hyacinthaceae as a separate family, merging it into a greatly enlarged family Asparagaceae. Thus Chionodoxa siehei moves from the Hyacinthaceae to the Asparagaceae.

• Taxonomists can disagree as to the rank of a taxon. Rather than allow the Hyacinthaceae to disappear altogether, Chase et al. suggested that it be treated as a subfamily within the Asparagaceae. The ICN requires family names to end with "-aceae" and subfamily names to end with "-oideae". Thus a possible name for the Hyacinthaceae when treated as a subfamily would be 'Hyacinthoideae'. However, the name Scilloideae had already been published in 1835 as the name for a subfamily containing the genus Scilla, so this name has priority and must be used. Hence for those taxonomists who accept that there should be a subfamily for Scilla and related genera, and accept the APG system of 2009, Chionodoxa siehei is placed in the subfamily Scilloideae of the family Asparagaceae. However, a taxonomist is perfectly free to continue to argue that Hyacinthaceae should be maintained as a separate family from the other families which were merged into the Asparagaceae.

In summary, if a plant has different names or is placed in differently named taxa:

• If the confusion is purely nomenclatural, i.e. it concerns what to call a taxon which has the same circumscription, rank and position, the ICN provides rules to settle the differences, typically by prescribing that the earliest published name must be used, although names can be conserved.
• If the confusion is taxonomic, i.e. taxonomists differ in opinion on the circumscription, rank or position of taxa, then only more scientific research can settle the differences.