Synonym (taxonomy)
Encyclopedia
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...

 of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name (under the currently used system of scientific nomenclature) to the Norway spruce
Norway Spruce
Norway Spruce is a species of spruce native to Europe. It is also commonly referred to as the European Spruce.- Description :...

, which he called Pinus abies. This name is no longer in use: it is now a synonym of the current scientific name which is Picea abies.

Unlike synonyms in other contexts, in taxonomy a synonym is not interchangeable with the name that it is a synonym of. In taxonomy synonyms are not equals, but have a different status. In general, for any taxon with a particular circumscription, position and rank only one scientific name is considered to be the correct one at any given time (this correct name is to be determined by applying the relevant Code of Nomenclature
Nomenclature Codes
Nomenclature codes or codes of nomenclature are the various rulebooks that govern biological taxonomic nomenclature, each in their own broad field of organisms...

). A synonym is always the synonym of a different scientific name and cannot exist in isolation. Given that the correct name of a taxon depends on the taxonomic viewpoint used (resulting in a particular circumscription, position and rank) a name that is one taxonomist's synonym may be another taxonomist's correct name (and vice versa).

Synonyms may arise whenever the same taxon is described and named more than once, independently. They may also arise whenever existing taxa are changed, as when a species is moved to a different genus, or two genera are joined to become one, etc.

General usage

To the general user of scientific names, in fields such as agriculture, horticulture, ecology, general science, etc., a synonym is a name that was previously used as the correct scientific name (in handbooks and similar sources) but which has been displaced by another scientific name, which is now regarded as correct. Thus Oxford Dictionaries Online defines the term as "a taxonomic name which has the same application as another, especially one which has been superseded and is no longer valid." In handbooks and general texts, it is useful to have synonyms mentioned as such after the current scientific name, so as to avoid confusion. For example, if the much advertised name change should go through and the scientific name of the fruit fly
Fruit fly
Fruit fly may refer to several organisms:* Tephritidae, a family of large, colorfully marked flies including agricultural pests* Drosophilidae, a family of smaller flies, including:** Drosophila, the genus of small fruit flies and vinegar flies...

 were changed to Sophophora melanogaster, it would be very helpful if any mention of this name was accompanied by "(syn. Drosophila melanogaster)". Synonyms used in this way may not always meet the strict definitions of the term "synonym" in the formal rules of nomenclature which govern scientific names (see below).

Changes of scientific name have two causes: they may be taxonomic or nomenclatural. A name change may be caused by changes in the circumscription, position or rank of a taxon, representing a change in taxonomic, scientific insight (as would be the case for the fruit fly, mentioned above). A name change may be due to purely nomenclatural reasons, that is, based on the rules of nomenclature; as for example when an older name is (re)discovered which has priority over the current name. Speaking in general, name changes for nomenclatural reasons have become less frequent over time as the rules of nomenclature allow for names to be conserved, so as to promote stability of scientific names.

Zoology

In zoological nomenclature, codified in the International Code of Zoological Nomenclature
International Code of Zoological Nomenclature
The International Code of Zoological Nomenclature is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals...

, synonyms are different scientific names of the same rank that pertain to the same taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...

, for example two names for the same species. The earliest such name is called the senior synonym, while the later names are junior synonyms. One basic principle of zoological nomenclature is that the earliest correctly published (and thus available
Available name
In zoology, an available name is a scientific name for a taxon of animals that has been published conforming to all the mandatory provisions of the ICZN Code for the establishment of a zoological name....

) name, the senior synonym, takes precedence and must be used for the taxon, if no other restrictions interfere. Synonyms are important because if the earliest name cannot be used (for example because the same spelling had previously been used for a name established for another taxon), then the next available junior synonym must be used for the taxon.

Objective synonyms refer to taxa with the same type and same rank (more or less the same taxon, although circumscription may vary, even widely). This may be species-group taxa of the same rank with the same type specimen, genus-group taxa of the same rank with the same type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...

 or if their type species are themselves objective synonyms, of family-group taxa with the same type genus, etc. In the case of subjective synonyms there is no such shared type, so the synonymy is open to taxonomic judgement, meaning that there is room for debate: one researcher might consider the two (or more) types to refer to one and the same taxon, another might consider them to belong to different taxa. For example, John Edward Gray
John Edward Gray
John Edward Gray, FRS was a British zoologist. He was the elder brother of George Robert Gray and son of the pharmacologist and botanist Samuel Frederick Gray ....

 published the name Antilocapra anteflexa in 1855 for a species of pronghorn
Pronghorn
The pronghorn is a species of artiodactyl mammal endemic to interior western and central North America. Though not an antelope, it is often known colloquially in North America as the prong buck, pronghorn antelope, or simply antelope, as it closely resembles the true antelopes of the Old World and...

, 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
George Ord
George Ord was an American ornithologist.Ord was born in Philadelphia, Pennsylvania. His father was a rope maker and Ord joined him in the business, continuing after his father's death in 1806...

 in 1815. Ord's name thus takes precedence, with Antilocapra anteflexa being a junior subjective synonym.

Objective synonyms are common at the level of genera, because for various reasons two genera may contain the same type species; these are objective synonyms. 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, which was established for a group of terrestrial snails containing as its type species the Burgundy or Roman snail Helix pomatia
Helix pomatia
Helix pomatia, common names the Burgundy snail, Roman snail, edible snail or escargot, is a species of large, edible, air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the family Helicidae...

– since Helix pomatia was already the type species for the genus Helix Linnaeus, 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 of 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. A common reason for objective synonyms at this level is when species are moved to a different genus: the above mentioned names of Felis leo and Panthera leo are objective synonyms. Another common reason for objective synonyms at this level is the creation of a replacement name.

It is possible for a junior synonym to be given precedence over a senior synonym, primarily when the senior name has not been used since 1899, and the junior name is in common use. The older name may be declared to be a nomen oblitum
Nomen oblitum
A nomen oblitum is a technical term, used in zoological nomenclature, for a particular kind of disused scientific name....

, and the junior name declared a nomen protectum. This rule exists 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
Petasina edentula
Petasina edentula is a species of air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the family Hygromiidae, the hairy snails and their allies....

(Draparnaud, 1805). In 2002, researchers found that an older name Helix depilata Draparnaud, 1801 referred to the same species, but this name had never been used after 1899 and was fixed as a nomen oblitum under this rule by Falkner et al. 2002.

Such a reversal of precedence is also possible if the senior synonym was established after 1900, but only if the International Commission on Zoological Nomenclature
International Commission on Zoological Nomenclature
The International Commission on Zoological Nomenclature is an organization dedicated to "achieving stability and sense in the scientific naming of animals". Founded in 1895, it currently comprises 28 members from 20 countries, mainly practicing zoological taxonomists...

 (ICZN) approves an application. For example, the scientific name of the red imported fire ant
Red imported fire ant
See main article Fire ant.The red imported fire ant , or simply RIFA, is one of over 280 species in the widespread genus Solenopsis...

, Solenopsis invicta was published by Buren in 1972, who did not know that this species was first named Solenopsis saevissima wagneri by Santschi in 1916; as there were thousands of publications using the name invicta before anyone discovered the synonymy, the ICZN, in 2001, ruled that invicta would be given precedence over wagneri.

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
Nomen nudum
The phrase nomen nudum is a Latin term, meaning "naked name", used in taxonomy...

) are not considered as synonyms in zoological nomenclature.

Botany

In botanical nomenclature
Botanical nomenclature
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...

, a synonym is a name that is not correct for the circumscription, position, and rank of the taxon as considered in the particular botanical publication. It is always "a synonym of the correct scientific name", but which name is correct depends on the taxonomic opinion of the author. In botany the various kinds of synonyms are:
  • Homotypic, or nomenclatural, synonyms have the same type. The Linnaean name Pinus abies L. has the same type as Picea abies (L.) H.Karst. When Picea is taken to be the correct genus for this species (there is almost complete consensus on that), Pinus abies is a homotypic synonym of Picea abies. However, if the species were considered 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; what matters is that it shares 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, or taxonomic, synonyms have different types. Some botanists split
    Lumpers and splitters
    Lumping and splitting refers to a well-known problem in any discipline which has to place individual examples into rigorously defined categories. The lumper/splitter problem occurs when there is the need to create classifications and assign examples to them, for example schools of literature,...

     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 listed synonym does not have to be a formally accepted scientific name (a validly published name): a listing of synonyms often contains designations that for some reason did not make it as a formal name (such as a herbarium name or manuscript name). Such a synonym must have the form of a formal name: it must look like a proper 'Latin name'.

Comparison between zoology and botany

Although the basic principles are fairly 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":
  • Synonyms in botany are comparable to "junior synonyms" in zoology.
  • The homotypic or nomenclatural synonyms in botany are comparable to "objective synonyms" in zoology.
  • The heterotypic or taxonomic synonyms in botany are comparable to "subjective synonyms" in zoology.

Synonym lists

Scientific papers may include lists of taxa, synonymizing existing taxa and (in some cases) listing references to them.

The status of a synonym may be indicated by symbols, as for instance in a system proposed for use in palaeontology by Rudolf Richter. In that system a v before the year would indicate that the authors have inspected the original material; a . that they take on the responsibility for the act of synonymizing the taxa.

Other usage

The traditional concept of synonymy is often expanded in taxonomic literature to include "pro parte" (or "for part") synonyms. These are caused by splits and circumscriptional changes. They are usually indicated by the abbreviation "p.p." For example:
  • When Dandy
    James Edgar Dandy
    James Edgar Dandy was a British botanist, Keeper of Botany, at the British Museum between 1956 and 1966.- References :...

     described Galium tricornutum
    Galium tricornutum
    Galium tricornutum is a species of flowering plant in the coffee family known by the common names rough corn bedstraw, roughfruit corn bedstraw, and corn cleavers. It can be found across much of the northern hemisphere, where it has a wide native range and has become naturalized in many areas...

    , he cited G. tricorne Stokes (1787) pro parte as a synonym, but explicitly excluded the type (specimen) of G. tricorne from the new species G. tricornutum. Thus G. tricorne was subdivided.
  • The Angiosperm Phylogeny Group
    Angiosperm Phylogeny Group
    The Angiosperm Phylogeny Group, or APG, refers to an informal international group of systematic botanists who came together to try to establish a consensus on the taxonomy of flowering plants that would reflect new knowledge about plant relationships discovered through phylogenetic studies., three...

    's summary of plant classification states that family Verbenaceae
    Verbenaceae
    Verbenaceae, commonly known as the verbena family or vervain family, is a family of mainly tropical flowering plants. It contains trees, shrubs and herbs notable for heads, spikes, or clusters of small flowers, many of which have an aromatic smell.Recent phylogenetic studies have shown that...

     "are much reduced compared to a decade or so ago, and many genera have been placed in Lamiaceae
    Lamiaceae
    The mints, taxonomically known as Lamiaceae or Labiatae, are a family of flowering plants. They have traditionally been considered closely related to Verbenaceae, but in the 1990s, phylogenetic studies suggested that many genera classified in Verbenaceae belong instead in Lamiaceae...

    ", but Avicennia
    Avicennia
    Avicennia is a genus of flowering plants currently placed in the bear's breeches family, Acanthaceae. It contains mangrove trees, which occur in the intertidal zones of estuarine areas and are characterized by aerial roots. Species of Avicennia occur worldwide south of the Tropic of Cancer.The...

    , which was once included in Verbenaceae has been moved to Acanthaceae
    Acanthaceae
    The family Acanthaceae is a taxon of dicotyledonous flowering plants containing almost 250 genera and about 2500 species....

    . Thus, it could be said that Verbenaceae pro parte is a synonym of Acanthaceae, and Verbenaceae pro parte is also a synonym of Lamiaceae. However, this terminology is rarely used because it is clearer to reserve the term "pro parte" for situations that divide a taxon that includes the type from one that does not.
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