Botanical nomenclature is the formal, scientific naming of plants. It is related to, but distinct from taxonomy. Plant taxonomy is concerned with grouping and classifying plants; botanical nomenclature then provides names for the results of this process. The starting point for modern botanical nomenclature is Linnaeus' Species Plantarum of 1753. Botanical nomenclature is governed by the International Code of Nomenclature for algae, fungi, and plants (ICN), which replaces the International Code of Botanical Nomenclature (ICBN).
History and scope 
Botanical nomenclature has a long history, going back to the period when Latin was the scientific language throughout Europe, and perhaps further back to Theophrastus. A key event was Linnaeus’ adoption of binomial names for plant species in his Species Plantarum (1753). Every plant species is given a name that remains the same no matter what other species were placed in the genus, and this separates taxonomy from nomenclature. These species names of Linnaeus together with names for other ranks (such as family, class, order, variety), can serve to express a great many taxonomic viewpoints.
In the nineteenth century it became increasingly clear that there was a need for rules to govern scientific nomenclature, and initiatives were taken to produce a body of laws. These were published in successively more sophisticated editions. For plants the key dates are 1867 (lois de Candolle), 1906 (International Rules of Botanical Nomenclature, 'Vienna Rules') and 1952 (International Code of Botanical Nomenclature, 'Stockholm Code'). The most recent is the Vienna Code, adopted in 2005.
Another development was the insight into the delimitation of the concept of 'plant'. Linnaeus held a much wider view of what a plant is than is acceptable today. Gradually more and more groups of organisms are being recognised as being independent of plants. Nevertheless the formal names of most of these organisms are governed by the (ICN), even today. A separate Code was adopted to govern the nomenclature of Bacteria, the ICNB.
All formal botanical names are governed by the ICN, and within the limits set by that code there is another set of rules, the International Code of Nomenclature for Cultivated Plants (ICNCP). This latter code applies to plant cultivars, that have been deliberately altered or selected by humans (see cultigen) and require separate recognition.
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.
See also 
(specific to botany)
- Botanical name
- International Code of Nomenclature for algae, fungi, and plants
- International Plant Names Index
- International Association for Plant Taxonomy
- Correct name (botany)
- Author citation (botany)
- Barkworth, M. (2004), Botanical Nomenclature (Nomenclature, Names, and Taxonomy), University of Utah, archived from the original on 2011-02-20, retrieved 2011-02-20
- McNeill, John; Barrie, F.R.; Burdet, H.M. et al., eds. (2006), International code of botanical nomenclature (Vienna Code) adopted by the seventeenth International Botanical Congress, Vienna, Austria, July 2005 (electronic ed.), Vienna: International Association for Plant Taxonomy, retrieved 2011-02-20
- McNeill et al. 2006, Principle IV
- Dashwood, Melanie & Mathew, Brian (2005), Hyacinthaceae – little blue bulbs (RHS Plant Trials and Awards, Bulletin Number 11), Royal Horticultural Society, archived from the original on 20 February 2011, retrieved 19 February 2011, p. 5
- McNeill et al. 2006, Principle III
- Angiosperm Phylogeny Group (1998), "An ordinal classification for the families of flowering plants", Annals of the Missouri Botanical Garden 85 (4): 531–553, doi:10.2307/2992015, retrieved 2011-02-19
- Angiosperm Phylogeny Group III (2009), "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III", Botanical Journal of the Linnean Society 161 (2): 105–121, doi:10.1111/j.1095-8339.2009.00996.x
- Chase, M.W.; Reveal, J.L. & Fay, M.F. (2009), "A subfamilial classification for the expanded asparagalean families Amaryllidaceae, Asparagaceae and Xanthorrhoeaceae", Botanical Journal of the Linnean Society 161 (2): 132–136, doi:10.1111/j.1095-8339.2009.00999.x
- McNeill et al. 2006, Article 19.1