Intaxonomy,binomial nomenclature ("two-term naming system"), also calledbinary nomenclature, is a formal system of namingspecies of living things by giving each a name composed of two parts, both of which useLatin grammatical forms, although they can be based on words from other languages. Such a name is called abinomial name (often shortened to just "binomial"), abinomen,[1]binominal name, or ascientific name; more informally, it is also called aLatin name. In theInternational Code of Zoological Nomenclature (ICZN), the system is also calledbinominal nomenclature,[2] with an "n" before the "al" in "binominal", which isnot a typographic error, meaning "two-name naming system".[1]
The first part of the name – thegeneric name – identifies thegenus to which the species belongs, whereas the second part – thespecific name orspecific epithet – distinguishes the species within the genus. For example, modern humans belong to the genusHomo and within this genus to the speciesHomo sapiens.Tyrannosaurus rex is likely the most widely known binomial.[3] Theformal introduction of this system of naming species is credited toCarl Linnaeus, effectively beginning with his workSpecies Plantarum in 1753.[4] But as early as 1622,Gaspard Bauhin introduced in his bookPinax theatri botanici (English,Illustrated exposition of plants) containing many names of genera that were later adopted by Linnaeus.[5] Binomial nomenclature was introduced in order to provide succinct, relatively stable and verifiable names that could be used and understood internationally, unlikecommon names which are usually different in every language.[6]
The application of binomial nomenclature is now governed by various internationally agreed codes of rules, of which the two most important are theInternational Code of Zoological Nomenclature (ICZN) for animals and theInternational Code of Nomenclature for algae, fungi, and plants (ICNafp orICN). Although the general principles underlying binomial nomenclature are common to these two codes, there are some differences in the terminology they use and their particular rules.
In modern usage, the first letter of the generic name is always capitalized in writing, while that of the specific epithet is not, even when derived from aproper noun such as the name of a person or place. Similarly, both parts areitalicized in normal text (or underlined in handwriting). Thus the binomial name of the annual phlox (named after botanistThomas Drummond) is now written asPhlox drummondii. Often, after a species name is introduced in a text, the generic name is abbreviated to the first letter in subsequent mentions (e.g.,P. drummondii).
In scientific works, theauthority for a binomial name is usually given, at least when it is first mentioned, and the year of publication may be specified.
"Patella vulgata Linnaeus, 1758". The name "Linnaeus" tells the reader who published the name, and description for this species; 1758 is the year the name and original description were published (in this case, in the10th edition of the bookSystema Naturae).
"Passer domesticus (Linnaeus, 1758)". The original name given by Linnaeus wasFringilla domestica; the parentheses indicate that the species is now placed in a different genus. The ICZN does not require that the name of the person who changed the genus be given, nor the date on which the change was made, although nomenclatorial catalogs usually include such information.
"Hyacinthoides italica (L.) Rothm." – Linnaeus first named this bluebell speciesScilla italica; Rothmaler transferred it to the genusHyacinthoides; theICNafp does not require that the dates of either publication be specified.
The wordbinomial is composed of two elements:bi- (Latin prefix meaning 'two') andnomial (theadjective form ofnomen, Latin for 'name'). In Medieval Latin, the related wordbinomium was used to signify one term in a binomial expression in mathematics.[7] In fact, the Latin wordbinomium may validly refer to either of the epithets in the binomial name, which can equally be referred to as abinomen (pl.binomina).[8]
Carl Linnaeus (1707–1778), a Swedish botanist, physician, and zoologist, invented the modern system of binomial nomenclature
Before the adoption of the modern binomial system of naming species, a scientific name consisted of a generic name combined with a specific name that was from one to several words long. Together they formed a system of polynomial nomenclature.[9] These names had two separate functions: to designate or label the species, and to be a diagnosis or description. These two goals were eventually found to be incompatible.[10] In a simple genus that contained few species, it was easy to tell them apart with a one-word genus and a one-word specific name; but as more species were discovered, the names necessarily became longer and unwieldy—for instance,Plantago foliis ovato-lanceolatus pubescentibus, spica cylindrica, scapo tereti ("plantain with pubescent ovate-lanceolate leaves, a cylindric spike and ateretescape"), which we know today asPlantago media.[11]
Such "polynomial names" may sometimes look like binomials, but are different. For example, Gerard's herbal (as amended by Johnson) describes various kinds of spiderwort: "The first is calledPhalangium ramosum, Branched Spiderwort; the second,Phalangium non ramosum, Unbranched Spiderwort. The other ... is aptly termedPhalangium Ephemerum Virginianum, Soon-Fading Spiderwort of Virginia".[12] The Latin phrases are short descriptions, rather than identifying labels.
TheBauhins, in particularCaspar Bauhin (1560–1624), took some important steps towards the binomial system by pruning the Latin descriptions, in many cases to two words.[13] The adoption by biologists of a system of strictly binomial nomenclature is due to Swedish botanist and physicianCarl Linnaeus (1707–1778). It was in his 1753Species Plantarum that Linnaeus began consistently using a one-wordtrivial name (nomen triviale) after a generic name (genus name) in a system of binomial nomenclature.[14] Trivial names had already appeared in hisCritica Botanica (1737) andPhilosophia Botanica (1751). This trivial name is what is now known as aspecific epithet (ICNafp) orspecific name (ICZN).[14] The Bauhins' genus names were retained in many of these, but the descriptive part was reduced to a single word.
Linnaeus's trivial names introduced the idea that the function of a name could simply be to give a species a unique label, meaning that the name no longer needed to be descriptive. Both parts could, for example, be derived from the names of people. Thus Gerard'sPhalangium ephemerum virginianum becameTradescantia virginiana, where the genus name honouredJohn Tradescant the Younger,[note 1] an English botanist and gardener.[15] A bird in the parrot family was namedPsittacus alexandri, meaning "Alexander's parrot", afterAlexander the Great, whose armies introduced eastern parakeets to Greece.[16] Linnaeus's trivial names were much easier to remember and use than the parallel polynomial names, and eventually replaced them.[4]
The value of the binomial nomenclature system derives primarily from its economy, its widespread use, and the uniqueness and stability of names that the Codes ofZoological andBotanical,Bacterial andViral Nomenclature provide:
Economy. Compared to the polynomial system which it replaced, a binomial name is shorter and easier to remember.[4] It corresponds to the noun-adjective form manyvernacular names take to indicate a species within a group (for example, 'brown bear' to refer to a particular type of bear),[6] as well as the widespread system offamily name plusgiven name(s) used to name people in many cultures.[13]
Uniqueness. Provided that taxonomists agree as to the limits of a species, it can have only one name that is correct under the appropriatenomenclature code, generally the earliest published if two or more names are accidentally assigned to a species.[18] This means the species a binomial name refers to can be clearly identified, as compared to the common names of species which are usually different in every language.[6] However, establishing that two names actually refer to the same species and then determining which has priority can sometimes be difficult, particularly if the species was named by biologists from different countries. Therefore, a species may have more than one regularly used name; all but one of these names are "synonyms".[19] Furthermore, within zoology or botany, each species name applies to only one species. If a name is used more than once, it is called ahomonym.
Stability. Although stability is far from absolute, the procedures associated with establishing binomial names, such as theprinciple of priority, tend to favor stability.[20] For example, when species are transferred between genera (as not uncommonly happens as a result of new knowledge), the second part of the binomial is kept the same (unless it becomes a homonym). Thus, there is disagreement among botanists as to whether the generaChionodoxa andScilla are sufficiently different for them to be kept separate. Those who keep them separate give the plant commonly grown in gardens in Europe the nameChionodoxa siehei; those who do not give it the nameScilla siehei.[21] Thesiehei element is constant. Similarly, if what were previously thought to be two distinct species are demoted to a lower rank, such as subspecies, the second part of the binomial name is retained as a trinomen (the third part of the new name). Thus, the Tenerife robin may be treated as a different species from the European robin, in which case its name isErithacus superbus, or as only a subspecies, in which case its name isErithacus rubecula superbus.[22] Thesuperbus element of the name is constant, as are its authorship and year of publication.
Binomial nomenclature for species has the effect that when a species is moved from one genus to another, sometimes the specific name or epithet must be changed as well. This may happen because the specific name is already used in the new genus, or toagree in gender with the new genus if the specific epithet is an adjective modifying the genus name. Some biologists have argued for the combination of the genus name and specific epithet into a single unambiguous name, or for the use of uninomials (as used in nomenclature of ranks above species).[23][24]
Because genus names are unique only within a nomenclature code, it is possible for homonyms (two or more species sharing the same genus name) to happen, and even the same binomial if they occur in different kingdoms. At least 1,258 instances of genus name duplication occur (mainly between zoology and botany).[25][26]
Nomenclature (including binomial nomenclature) is not the same as classification, although the two are related. Classification is the ordering of items into groups based on similarities or differences; inbiological classification, species are one of the kinds of item to be classified.[27] In principle, the names given to species could be completely independent of their classification. This is not the case for binomial names, since the first part of a binomial is the name of the genus into which the species is placed. Above the rank of genus, binomial nomenclature and classification are partly independent; for example, a species retains its binomial name if it is moved from one family to another or from one order to another, unless it better fits a different genus in the same or different family, or it is split from its old genus and placed in a newly created genus. The independence is only partial since the names of families and other higher taxa are usually based on genera.
Taxonomy includes both nomenclature and classification. Its first stages (sometimes called "alpha taxonomy") are concerned with finding, describing and naming species of living orfossil organisms.[28] Binomial nomenclature is thus an important part of taxonomy as it is the system by which species are named. Taxonomists are also concerned with classification, including its principles, procedures and rules.[29]
A complete binomial name is always treated grammatically as if it were a phrase in the Latin language (hence the common use of the term "Latin name" for a binomial name). However, the two parts of a binomial name can each be derived from a number of sources, of which Latin is only one. These include:
Latin, from any period, whetherclassical,medieval ormodern. Thus, both parts of the binomial nameHomo sapiens are Latin words, meaning "wise" (sapiens) "human/man" (Homo).
Classical Greek. The genusRhododendron was named byLinnaeus from the Greek wordῥοδόδενδρον, itself derived fromrhodon, "rose", anddendron, "tree".[30][31] Greek words are often converted to a Latinized form. Thus coca (the plant from which cocaine is obtained) has the nameErythroxylum coca.Erythroxylum is derived from the Greek wordserythros, red, andxylon, wood.[32] The Greek ending -ον (-on), when it is neuter, is often converted to the Latin neuter ending-um.[note 2]
Other languages. The second part of the nameErythroxylum coca is derived fromkuka, the name of the plant inAymara andQuechua.[33][34] Since many dinosaur fossils were found in Mongolia, their names often useMongolian words, e.g.Tarchia fromtarkhi, meaning "brain", orSaichania meaning "beautiful one".
The first part of the name, which identifies the genus, must be a word that can be treated as a Latinsingular noun in thenominative case. It must be unique within the purview of eachnomenclatural code, but can be repeated between them. ThusHuia recurvata is an extinct species of plant, found asfossils inYunnan, China,[39] whereasHuia masonii is a species of frog found inJava, Indonesia.[40]
The second part of the name, which identifies the species within the genus, is also treated grammatically as a Latin word. It can have one of a number of forms:
The second part of a binomial may be an adjective. If so, the form of the adjective must agree with the genus name ingender. Latin nouns can have three genders, masculine, feminine and neuter, and many Latin adjectives will have two or three different endings, depending upon the gender of the noun they refer to. Thehouse sparrow has the binomial namePasser domesticus. Heredomesticus ("domestic") simply means "associated with the house". Thesacred bamboo isNandina domestica[41] rather thanNandina domesticus, sinceNandina is feminine whereasPasser is masculine. The tropical fruitlangsat is a product of the plantLansium parasiticum, sinceLansium is neuter. Some common endings for Latin adjectives in the three genders (masculine, feminine, neuter) are-us,-a,-um (as in the previous example ofdomesticus);-is,-is,-e (e.g.,tristis, meaning "sad"); and-or-or-us (e.g.,minor, meaning "smaller"). For further information, seeLatin declension: Adjectives.
The second part of a binomial may be a noun in the nominative case. An example is the binomial name of the lion, which isPanthera leo. Grammatically the noun is said to be inapposition to the genus name and the two nouns do not have to agree in gender; in this case,Panthera is feminine andleo is masculine.
The second part of a binomial may be a noun in thegenitive (possessive) case. The genitive case is constructed in a number of ways in Latin, depending on thedeclension of the noun. Common endings for masculine and neuter nouns are-ii or-i in the singular and-orum in the plural, and for feminine nouns-ae in the singular and-arum in the plural. The noun may be part of a person's name, often the surname, as in theTibetan antelope (Pantholops hodgsonii), the shrubMagnolia hodgsonii, or theolive-backed pipit (Anthus hodgsoni). The meaning is "of the person named", soMagnolia hodgsonii means "Hodgson's magnolia". The-ii or-i endings show that in each case Hodgson was a man (not the same one); had Hodgson been a woman,hodgsonae would have been used. The person commemorated in the binomial name is not usually (if ever) the person who created the name; for example,Anthus hodgsoni was named byCharles Wallace Richmond, in honour of Hodgson. Rather than a person, the noun may be related to a place, as withLatimeria chalumnae, meaning "of theChalumna River". Another use of genitive nouns is in, for example, the name of the bacteriumEscherichia coli, wherecoli means "of thecolon". This formation is common in parasites, as inXenos vesparum, wherevesparum means "of the wasps", sinceXenos vesparum is a parasite of wasps.
Whereas the first part of a binomial name must be unique within the purview of each nomenclatural code, the second part is quite commonly used in two or more genera (as is shown by examples ofhodgsonii above), but cannot be used more than once within a single genus. The full binomial name must be unique within each code.
"Binomial nomenclature" is the correct term for botany,[43] although it is also used by zoologists.[44] Since 1961,[45] "binominal nomenclature" is the technically correct term in zoology.[2] A binomial name is also called a binomen (plural binomina) or binominal name.[1]
Both codes consider the first part of the two-part name for a species to be the "generic name". In the zoological code (ICZN), the second part of the name is a "specific name". In the botanical code (ICNafp), it is a "specific epithet". Together, these two parts are referred to as a "species name" or "binomen" in the zoological code: or "species name", "binomial", or "binary combination" in the botanical code. "Species name" is the only term common to the two codes.
TheICNafp, the plant code, does not allow the two parts of a binomial name to be the same (such a name is called atautonym), whereas theICZN, the animal code, does. Thus the American bison has the binomenBison bison; a name of this kind would not be allowed for a plant.
The starting points, the time from which these codes are in effect (retroactively), vary from group to group. Inbotany the starting point will often be in 1753 (the year Carl Linnaeus first publishedSpecies Plantarum). Inzoology the starting point is 1758 (1 January 1758 is considered the date of the publication of Linnaeus'sSystema Naturae, 10th Edition, and alsoClerck'sAranei Svecici).Bacteriology started anew, with a starting point on 1 January 1980.[46]
Summary of terminology for the names of species in the ICZN and ICNafp
Code
Full name
First part
Second part
ICZN
species name, binomen, binominal name
generic name, genus name
specific name
ICNafp
species name, binary combination, binomial (name)
generic name
specific epithet
Unifying the different codes into a single code, the "BioCode", has been suggested,[47] although implementation is not in sight. (There is also a published code for a different system of biotic nomenclature, which does not use ranks above species, but instead namesclades. This is calledPhyloCode.)
As noted above, there are some differences between the codes in how binomials can be formed; for example theICZN allows both parts to be the same, while theICNafp does not. Another difference is in how personal names are used in forming specific names or epithets. TheICNafp sets out precise rules by which a personal name is to be converted to a specific epithet. In particular, names ending in a consonant (but not "er") are treated as first being converted into Latin by adding "-ius" (for a man) or "-ia" (for a woman), and then being made genitive (i.e. meaning "of that person or persons"). This produces specific epithets likelecardii for Lecard (male),wilsoniae for Wilson (female), andbrauniarum for the Braun sisters.[48] By contrast, theICZN does not require the intermediate creation of a Latin form of a personal name, allowing the genitive ending to be added directly to the personal name.[49] This explains the difference between the names of the plantMagnolia hodgsonii and the birdAnthus hodgsoni. Furthermore, theICNafp requires names not published in the form required by the code to be corrected to conform to it,[50] whereas theICZN is more protective of the form used by the original author.[51]
By tradition, the binomial names of species are usually typeset in italics; for example,Homo sapiens.[52] Generally, the binomial should be printed in afont style different from that used in the normal text; for example, "Several moreHomo sapiens fossils were discovered." When handwritten, a binomial name should be underlined; for example,Homosapiens.[53]
The first part of the binomial, the genus name, is always written with an initial capital letter. Older sources, particularly botanical works published before the 1950s, used a different convention: if the second part of the name was derived from a proper noun, e.g., the name of a person or place, a capital letter was used. Thus, the modern formBerberis darwinii was written asBerberis Darwinii. A capital was also used when the name is formed by two nouns in apposition, e.g.,Panthera Leo orCentaurea Cyanus.[54][note 3] In current usage, the second part is never written with an initial capital.[56][57]
When used with a common name, the scientific name often follows in parentheses, although this varies with publication.[58] For example, "The house sparrow (Passer domesticus) is decreasing in Europe."
The binomial name should generally be written in full. The exception to this is when several species from the same genus are being listed or discussed in the same paper or report, or the same species is mentioned repeatedly; in which case the genus is written in full when it is first used, but may then be abbreviated to an initial (and a period/full stop).[59] For example, a list of members of the genusCanis might be written as "Canis lupus,C. aureus,C. simensis". In rare cases, this abbreviated form has spread to more general use; for example, the bacteriumEscherichia coli is often referred to as justE. coli, andTyrannosaurus rex is perhaps even better known simply asT. rex, these two both often appearing in this form in popular writing even where the full genus name has not already been given.
The abbreviation "sp." is used when the actual specific name cannot or need not be specified. The abbreviation "spp." (standing forspecies pluralis, Latin for "multiple species") indicates "several species". These abbreviations are not italicised (or underlined).[60][61] For example: "Canis sp." means "an unspecified species of the genusCanis", while "Canis spp." means "two or more species of the genusCanis". (These abbreviations should not be confused with the abbreviations "ssp." (zoology) or "subsp." (botany), plurals "sspp." or "subspp.", referring to one or moresubspecies. Seetrinomen (zoology) andinfraspecific name.)
The abbreviation "cf." (i.e.,confer in Latin) is used to compare individuals/taxa with known/described species. Conventions for use of the "cf." qualifier vary.[62] In paleontology, it is typically used when the identification is not confirmed.[63] For example, "Corvus cf.nasicus" was used to indicate "a fossil bird similar to theCuban crow but not certainly identified as this species".[64] In molecular systematics papers, "cf." may be used to indicate one or more undescribed species assumed to be related to a described species. For example, in a paper describing the phylogeny of small benthic freshwater fish called darters, five undescribed putative species (Ozark, Sheltowee, Wildcat, Ihiyo, and Mamequit darters), notable for brightly colored nuptial males with distinctive color patterns,[65] were referred to as "Etheostoma cf.spectabile" because they had been viewed as related to, but distinct from,Etheostoma spectabile (orangethroat darter).[66] This view was supported to varying degrees by DNA analysis. The somewhat informal use of taxa names with qualifying abbreviations is referred to asopen nomenclature and it is not subject to strict usage codes.
In some contexts, the dagger symbol ("†") may be used before or after the binomial name to indicate that the species is extinct.
In scholarly texts, at least the first or main use of the binomial name is usually followed by the "authority" – a way of designating the scientist(s) who first published the name. The authority is written in slightly different ways in zoology and botany. For names governed by theICZN the surname is usually written in full together with the date (normally only the year) of publication. One example of author citation of scientific name is: "Amabela Möschler, 1880."[note 4] TheICZN recommends that the "original author and date of a name should be cited at least once in each work dealing with the taxon denoted by that name."[67] For names governed by theICNafp the name is generally reduced to a standard abbreviation and the date omitted. TheInternational Plant Names Index maintains an approved list of botanical author abbreviations. Historically, abbreviations were used in zoology too.
When the original name is changed, e.g., the species is moved to a different genus, both codes use parentheses around the original authority; theICNafp also requires the person who made the change to be given. In theICNafp, the original name is then called thebasionym. Some examples:
(Plant)Amaranthus retroflexus L. – "L." is the standard abbreviation for "Linnaeus"; the absence of parentheses shows that this is his original name.
(Plant)Hyacinthoides italica (L.) Rothm. – Linnaeus first named the Italian bluebellScilla italica; that is the basionym.Rothmaler later transferred it to the genusHyacinthoides.
(Animal)Passer domesticus (Linnaeus, 1758) – the original name given by Linnaeus wasFringilla domestica; unlike theICNafp, theICZN does not require the name of the person who changed the genus (Mathurin Jacques Brisson[68]) to be given.
Binomial nomenclature, as described here, is a system for naming species. Implicitly, it includes a system for naming genera, since the first part of the name of the species is a genus name. In a classification system based on ranks, there are also ways of naming ranks above the level of genus and below the level of species. Ranks above genus (e.g., family, order, class) receive one-part names, which are conventionally not written in italics. Thus, the house sparrow,Passer domesticus, belongs to the familyPasseridae.Family names are normally based on genus names, such as in zoology,[69] although the endings used differ between zoology and botany.
Ranks below species receive three-part names, conventionally written in italics like the names of species. There are significant differences between theICZN and theICNafp. In zoology, the only formal rank below species is subspecies and the name is written simply as three parts (a trinomen). Thus, one of the subspecies of theolive-backed pipit isAnthus hodgsoni berezowskii. Informally, in some circumstances, aform may be appended, though such names are unavailable, and have no formal standing in zoological nomenclature (i.e., they have no recognized author or date, and do not compete for homonymy). For exampleHarmonia axyridis f.spectabilis is the harlequin ladybird in its black or melanic forms having four large orange or red spots. In botany, there are many ranks below species and although the name itself is written in three parts, a "connecting term" (not part of the name) is needed to show the rank. Thus, the American black elder isSambucus nigra subsp.canadensis; the white-flowered form of the ivy-leaved cyclamen isCyclamen hederifolium f.albiflorum.[70]
^Some sources say that both John Tradescant the Younger and his father,John Tradescant the Elder, were intended by Linnaeus.
^The ending "-on" may derive from the neuter Greek ending -ον, as inRhodoxylon floridum, or the masculine Greek ending -ων, as inRhodochiton atrosanguineus.
^The modern notation was resisted by some, partly because writing names likeCentaurea cyanus can suggest thatcyanus is an adjective which should agree withCentaurea, i.e. that the name should beCentaurea cyana, whereasCyanus is derived from the Greek name for the cornflower.[55]
^Here Amabela is the name of thegenus. It is written in italic form. Followed by the last name of the scientist who discovered it (Heinrich BennoMöschler), a comma, and the year when it was published.
^Bauhin, Gaspard."Pinax theatri botanici". Kyoto University Library.Archived from the original on 17 October 2016. Retrieved19 June 2016.
^abcStearn, William T. (1959). "The Background of Linnaeus's Contributions to the Nomenclature and Methods of Systematic Biology".Systematic Zoology.8 (1):4–22.doi:10.2307/2411603.JSTOR2411603.
^"binôme".Le Trésor de la langue française informatisé. Centre National de Ressources Textuelles et Lexicales. Archived fromthe original on 6 June 2017.
^abJohnson, A. T.; Smith, H. A.; Stockdale, A. P. (2019).Plant Names Simplified: Their Pronunciation Derivation & Meaning. Sheffield, Yorkshire: 5M Publishing.ISBN978-1-910455-06-7., p. v
^Michener, Charles D. (1964). "The possible use of uninominal nomenclature to increase the stability of names in biology".Systematic Zoology.13 (4):182–190.doi:10.2307/2411777.JSTOR2411777.
^Radio San Gabriel, "Instituto Radiofonico de Promoción Aymara" (IRPA) 1993, Republicado por Instituto de las Lenguas y Literaturas Andinas-Amazónicas (ILLLA-A) 2011, Transcripción del Vocabulario de la Lengua Aymara, P.Ludovico Bertonio 1612 (Spanish-Aymara-Aymara-Spanish dictionary)
^Evenhuis, Neal L. (2002). "Pieza, a new genus of microbombyliids from the New World (Diptera: Mythicomyiidae)".Zootaxa.36 (1):1–28.doi:10.11646/zootaxa.36.1.1.
^Tan, Hugh T.W.; Tan, Kai-xin."Understanding and Learning Scientific Names of Species".CDTL.NUS.edu.sg. Successful Learning, Center for Development of Teaching and Learning, National University of Singapore.Archived from the original on 21 July 2011. Retrieved20 June 2011.
^Gilbert-Carter, H. (1955).Glossary of the British Flora (2nd ed.). Cambridge University Press. p. xix.OCLC559413416.
^Silyn-Roberts, Heather (2000).Writing for Science and Engineering: Papers, Presentations and Reports. Oxford; Boston: Butterworth-Heinemann. p. 198.ISBN978-0-7506-4636-9.
^Jenks, Matthew A."Plant Nomenclature".Hort.Purdue.edu. Department of Horticulture and Landscape Architecture, Purdue University. Archived fromthe original on 11 December 2012. Retrieved20 June 2011.
^Summers-Smith, J. Denis (1988).The Sparrows. illustrated by Robert Gillmor. Calton, Staffordshire, England: T. & A. D. Poyser. pp. 114–115.ISBN978-0-85661-048-6.
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