In scientific nomenclature, synonyms are different scientific names used for a single taxon. Usage and terminology are different for zoology and botany.
Contents |
In zoological nomenclature, synonyms are different scientific names that pertain to the same taxon, for example two names for the same species. The rule of zoological nomenclature is that the first name to be published is the senior synonym; any others are junior synonyms and should not be used.
Objective synonyms unambiguously refer to the same taxon; this is the case if they refer to the same description or the same type specimen or type species[1]. Otherwise the synonyms are subjective synonyms[2], meaning that there is room for debate: one researcher might consider the two (or more) types or descriptions to refer to one and the same taxon, another might consider them distinct.
For example, John Edward Gray published the name Antilocapra anteflexa in 1855 for a species of pronghorn, based on a pair of horns. However, it is now commonly accepted that his specimen was an unusual individual of the species Antilocapra americana published by George Ord in 1815. Ord's name thus takes priority, with Antilocapra anteflexa being a junior subjective synonym.
Objective synonyms are common at the level of genera, because for various reasons two genera may obtain the same type species; these are objective synonyms[3]. In many cases researchers established new generic names because they thought this was necessary or did not know that others had previously established another genus for the same group of species. An example is the genus Pomatia Beck, 1837[4] which was established for a group of terrestrial snails containing as its type species the Burgundy or Roman snail Helix pomatia - since Helix pomatia was already the type species for the genus Helix Linnæus, 1758, the genus Pomatia was an objective synonym (and useless). At the same occasion Helix is also a synonym of 'Pomatia, but it is older and so it has precedence.
At the species level, subjective synonyms are common because an unexpectedly large range of variation in a species, or simple ignorance about an earlier description, may lead a biologist to describe a newly discovered specimen as a new species. However, objective synonyms are quite rare because it must be established that two names must be based on the same and only one type specimen[5].
It is possible for a junior synonym to be given precedence over a senior synonym[6], primarily when the senior name has not been used since 1899, and the junior name is in common use. The older name becomes a nomen oblitum, and the junior name is declared a nomen protectum. This is primarily to prevent the confusion that would result if a well-known name, with a large accompanying body of literature, were to be replaced by a completely unfamiliar name. An example is the European land snail Petasina edentula (Draparnaud, 1805). In 2002 researchers found that an older name Helix depilata Draparnaud, 1801 referred to the same species - this name had never been used after 1899 and was fixed by Falkner et al. 2002[7] as a nomen oblitum under this rule.
Such a reversal of precedence is also possible if the senior synonym was established after 1900, but only if the ICZN Commission approves an application. For example, the scientific name of the red imported fire ant, Solenopsis invicta, was published by Buren in 1972, and is a specific name that has been conserved, despite the fact that this species was first named Solenopsis saevissima wagneri by Santschi in 1916; there are thousands of publications that had been published using the name invicta before anyone discovered the synonymy, and, in 2001, the ICZN ruled that invicta would be given precedence over wagneri.
In zoology there is no synonymy if a specific name is placed in a different genus. An example is the snow leopard, originally described as Felis uncia [Schreber], 1776, which is now known either as Uncia uncia ([Schreber], 1776) or as Panthera uncia ([Schreber], 1776). These two names are not synonyms, but are referred to in zoology as different "combinations" of the same specific name. If the specific name is placed in a different genus than the one in which it had originally been described, the name of the original author is only set in parentheses.
To qualify as a synonym in zoology a name must be properly published in accordance with the rules. Manuscript names and names that were mentioned without any description (nomina nuda) cannot be synonyms.
In botanical nomenclature, the synonym of a botanical name is a name that also applies to this same taxon. A synonym cannot exist in isolation: it is always "a synonym of ...". In botany synonyms can be:
| Type | Name | Definition |
|---|---|---|
| homotypic | nomenclatural | having the same type. The Linnaean name Pinus abies L. has the same type as Picea abies (L.) H.Karst. When the latter is taken to be the correct name (there is almost complete consensus on that), Pinus abies is a homotypic synonym of Picea abies. However, if the species were regarded to belong to Pinus (now unlikely) the relationship would be reversed and Picea abies would become a homotypic synonym of Pinus abies.
A homotypic synonym need not share an epithet or name with the correct name, but only the type. For example the name Taraxacum officinale, mentioned above, has the same type as Leontodon taraxacum L. The latter is a homotypic synonym of Taraxacum officinale F.H.Wigg. |
| heterotypic | taxonomic | with a different type. Some botanists split the dandelion into many, quite restricted species. The name of each such species has its own type. When the dandelion is regarded as including all those small species, the names of all those species are heterotypic synonyms of Taraxacum officinale F.H.Wigg. Reducing a taxon to a heterotypic synonym is termed "to sink in synonymy" or "as synonym". |
In botany a name that is placed in a different genus is a different name in terms of synonymy; in contrast to zoology it possesses an additional authority (which is the name of the person who first placed it in the different genus, which is set in parentheses after the first author who originally established the name).
In botany it is not required that a synonym be a valid name: a listing of synonyms often contains names that for some reason did not make it as a formal name (unpublished or manuscript names), or have not yet been formally published. Such a synonym must have the form of a formal name: it must look like a proper 'Latin name'.
Although the basic principles are similar, the treatment of synonyms in botanical nomenclature differs in detail and terminology from zoological nomenclature, where the correct name is included among synonyms, although as first among equals it is the "senior synonym":
The traditional concept of synonymy is often expanded in taxonomic databases to include pro parte (or "in part") synonyms. These are caused by splits and circumscriptional changes and do not require a one to one association with types. A single name could actually refer to several taxa because the original name is now used in a more restricted sense. They are usually indicated by the abbreviation p.p.. [8]
Blackwelder, R. A. (1966). Taxonomy: A text and reference book. New York: Wiley.