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Binomial nomenclature

 Binomial nomenclature

The process of assigning of scientific names to plants is known as nomenclature. Name is the most important way for identification of plants. Our choice of names for individual imbibes a great influence on language, religion, culture and tradition. Thus, there is a need of an internationally accepted terminology and names in Botanic study so that our work can be meaningful and comprehensive one to all concerned.

Why it was needed to designate a scientific name:

Plants are innumerable and most of the plants do not have common names. Common names are mostly local and they vary from language to language, from country to country and even from area to area, e.g. Mango (Mangifera indica) has about 50 common names .Therefore, common names are proved to be ineffective for wider use throughout the country or the world.

 

Problems possessed by common names:

Botanists prefer scientific names instead of common names as common names pose some problems, such as

  • Common names are not universal and can be applied in just one or two languages, e.g. in England, the common name for Hibiscus esculentusis Lady’s finger whereas in Pakistan it is Bhindi.
  • The common names do not provide any information about generic and family relationship.
  • Sometimes there may be two or more plants which have the same common names.  
  • Some rare one species do not have common names.

Binomial Nomenclature

The assignment of scientific names involves principles governed by rules adopted by the International Botanical Congresses. The main goal of this system is to provide one correct name for each taxon. Scientific names are to be designed in Latin because,

  1. This language is not to be used as a local language in any nation or country
  2. It is widely used language by European countries and therefore a lot of literature is available in Latin.

Plants were named in such a way that each name consists of three or more words. These names were called as polynomials.But this polynomial use remained in   practice till end of the Eighteenth century. In 1753, Linnaeus substituted the polynomials with binomials and published his work in book “ Species Plantarum”. This Binomial format made naming more convenient. Thus, it has provided a readily expandable system.

Word Study: Bi means two (2) and Nomenclature means naming. A system in which a two word name is given to organisms is termed as binomial nomenclature.

Presenter: Presented by C. Linnaeus

Composition of Binomial Format:

A binomial consists up of a Genus Name and Specific Epithet called the Species Name, e.g. Quercus alba L is the scientific name of white oak in which Quercus is the Genus while alba is the specific epithet and author name Linnaeus (L).

  1. Generic Name:

The generic name is Latinized word treated as noun. It should be written in Latin starting with a Capital letter. It can also be abbreviated by using the first capital letter, e.g. Q for “Quercus”.

  1. Specific Epithets:

The specific epithet is mostly an adjective showing a distinguishing feature of the plant. It is derived from a source or old common name or composed arbitrarily.

  • Auther:

The name of the person following the specific epithet represents the author’s name which acts as source of historical information regarding that name.

For example, L” for Linneaus. It is placed after each plant binomial which is related to Linneaus.

Rules of Nomenclature:

After the development of order and stability in Plant nomenclature, today Botanists in all over the world use the International code of Nomenclature, which is written in many European languages. This code includes 6 Principles, 75 Rules, 57 Recommendations and many notes and examples. Some important principles, rules ad recommendations are as follows:

  1. Independence on Zoological Nomenclature:

The name of a plant must not be rejected if it is identical to the name of an animal. Thus, plant nomenclature is totally independent of zoological nomenclature.

  1. Latinized Binomial:

Scientific names should be treated as Latin. Both Generic name and the specific epithet should be from Latin language. The generic name should starts with a capital letter and the specific epithet should start with a small letter.

  • Effective Valid Publication:

The names of publications must be effective and valid. Effectiveness and validity are discussed as under;

  • Effective publicationmeans the name must be published in a periodical, which must be distributed to all the botanical centers of the world.
  • Valid publicationmeans the name is accompanied by the description of the individual.
  1. Retention, Choice and Rejection:

In a Binomial, if the specific epithet is exactly similar to the generic name then it is termed as Tautonym.

  • Tautonymy is strictly banned in Botany. Thus, in this case a new specific epithet should be assigned to the plant.
  • Two plants with same epithet must not occur in the same genus. If it occurs, they are termed as Homonyms. In this case, the earlier valid name must be retained.
  1. Priority of Names:

Priority depends upon the precedence of the date of valid publication.

  1. Ranks of Taxa:

Each species belongs to a number of taxa which is a series of genus, family, order, sub-class, class, sub-division and division. The name of a division must end in “phyta”, class in “opsida”, order in “ales” and family in “aceae”.

  • Citation of Author’s name:

The name of the author who firstly validly published name of that plant must be cited at the end of Binomial.

  • Type concept:

The type method is to be used as a device to provide correct names of taxa. The several types designated by the system are as follows:

  • Holotype
  • Isotype
  • Lectotype
  • Syntype
  • Paratype
  • Neotype

This system of types is called for acceptable substitutes.

Carolus Linnaeus(1707-1778 AD) first introduced and adopted the system of binomial nomenclature. As the word “binomial” suggests, the scientific name of a species consists of two names: the first is genus name and the second one is the name of species.

Rules, Bases and Principles for assigning scientific names: some rule for assigning scientific names are as follows.

  • Scientific names are usually printed in italics, such as Homo sapiens. When handwritten they are underlined.
  • The first term (generic name) always begins with capital letter, while species name is never capitalized (even when derived from a proper name).
  • The scientific name is generally written in full when it is first used. But when several species from the same genus are being listed, it may then be abbreviated by just using an initial for genus; for example Escherichia coli becomes E. coli.

Aims and Significance of Binomial nomenclature:

In biological research, common names cause many problems. Different regions have different names for the same organism. For example; common name of onion in Urdu is ‘Piyaz’ but in different regions of Pakistan it is also known as ‘ganda’ or ‘bassal’ or ‘vassal’. In other countries, it has other sets of names. In science, it is known with a single name as Allium cepa. In some cases, different organisms are called by the same common name. For example; the name ‘black bird’ is used for crow as well as for raven.

Common names have no scientific basis. For example; a fish is a vertebrate animal with fins and gills. But several common names of ‘silver fish’, ‘cray fish’, ‘jelly fish’, and ‘star fish’ do not fit the biologist’s definition of a fish. To avoid all these confusions, organisms are given scientific names by using binomial nomenclature . The value of this system is due to its widespread use and the stability of its names. In binomial nomenclature, every species can be unambiguously identified with just two words. Same name can be used all over the world, in all languages, avoiding difficulties of translation.

 

Examples:

Common Name

Scientific Name

Onion

Allium cepa

Common sea star (starfish)

Asterias rubens

House crow

Corvus splendens

 

 

Sometime organisms are named in honor of the research workers who described and classified them. For example; the Orchid tree (Mountain-ebony) was named as Bauhinia variegata after the Swiss botanists Bauhin. Bauhinia variegata is an ornamental tree found in southeast Asia.

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