Basionym, in the scientific name of organisms, means the 'original name' on which a new name is based. The term is primarily used in botanical nomenclature, the scientific naming of plants. Use of the term "basionym" is regulated by the International Code of Botanical Nomenclature, where it is defined as:
- basionym. The legitimate, previously published name on which a new combination or name at new rank is based. ... (Art. 6.10)
The term 'basionym' indicates which name was the original, validly published name of the taxon. For instance, when the binomial name of a species changes (for taxonomic or nomenclatural reasons), the earliest name is the basionym. For example, the basionym of the name Picea abies (the Norway Spruce) is Pinus abies. The species was originally named Pinus abies by Carolus Linnaeus; later on, botanist Karsten decided this species should not be grouped in the same genus Pinus as the pines, but in a separate genus, so he transferred it to the genus Picea (the spruces).
A binomial name is treated as a Latin phrase in two words, no matter which language the words originally derive from. In a binomial name, the second part, the species name, is sometimes called the epithet. When the epithet is an adjective, rather than a noun in apposition, the ending of the epithet must always follow the gender of the genus name. When the genus is changed, there may be a change in the spelling in the epithet. For example the current name of one species of seaweed or alga, Acrocarpia paniculata (feminine) has the basionym Fucus paniculatus (masculine).
In 1768, the species Cactus opuntia (L.) 1754 was renamed by Miller Opuntia ficus-indica (L.) Mill. 1768; the basionym which is a species name, provides the stem of the new name at the rank of genus.
- McNeill, J.; Barrie, F.R.; Buck, W.R.; Demoulin, V.; Greuter, W.; Hawksworth, D.L.; Herendeen, P.S.; Knapp, S.; Marhold, K.; Prado, J.; Prud'homme Van Reine, W.F.; Smith, G.F.; Wiersema, J.H.; Turland, N.J. (2012). "Glossary". International Code of Nomenclature for algae, fungi, and plants (Melbourne Code) adopted by the Eighteenth International Botanical Congress Melbourne, Australia, July 2011. Regnum Vegetabile 154. A.R.G. Gantner Verlag KG. ISBN 978-3-87429-425-6.
- Tindall, B. J. (1999), "Misunderstanding the Bacteriological Code", International Journal of Systematic Bacteriology 49 (3): 1313–1316, doi:10.1099/00207713-49-3-1313, PMID 10425796, retrieved 2008-07-28