Binomial nomenclature and taxonomic hierarchy
Posted on : 24-11-2017 Posted by : Admin

 

BINOMIAL NOMENCLATURE

Taxonomy is the science of classifying and identifying plants. Scientific names are necessary because the same common name is used for different plants in different areas of the world. Latin is the language used for scientific classification.

Binomial nomenclature system is the one where the name of the plant consists of two parts – genus name and species name. It is developed by Carolus Linnaeus.

Guidelines for naming the plants

  •   Generic name is always capitalized.
  •   Specific epithet is never capitalized (if person’s name is involved).
  •   Either underlined or italicized.
  •   Authors name is never italicized (unless it the name of a Botanist in honor)
  •   When listing of several plants from same genus, Full genus name first and later capitalized initial for subsequent species.
  •   Sp. /spp. is written when exact species is not known.

Generic name: Generic name is the first word of the Binomial name. The first letter is capital. It is singular noun. The generic names are coined from different sources.

1. The genus may be named in honor of a botanist

For ex: Linnea for Linnaeus

Adansonia- Michel Adanson

Bauhinia – Casper Bauhin

2. In many cases generic names express some features of a plant

For ex: Pterospermum (winged seeds)

Trifolium – plant having three leaflets.

Acanthospermum- Spiny fruit

3. Some generic names are mythological or poetic.

For ex: Theobroma (Gods food)

4. Sometimes generic name is given after a name of a place (country, mountain or river)

For ex: Araucaria – Arauca province of Chile

Cassia – Mountain cassia from N.Syria

Salvadora – El. salvadore

Specific name: It is the second word of the Binomial name. Its first letter is small and is an adjective. The generic names are coined from different sources.

1. It may be description of a plant.

Color of the plant or plant part, For example: alba (white), nigra (black)

Habitat of the plant, For example: aquatica(in water), arvensis (in fields)

2. It may be in the honor of some botanist, For example: roxburghii (Vanda roxburghii)

3. Specific name may be constructed from noun, For example: bignoniodes (Bignonia)

4. It may be a descriptive adjective, For example: cordifolia (heart shaped leaves)

Advantages of Binomial names

These name are simple

  1. These are universal names and hence remain constant in different places, languages. This avoids confusions, effective in   communication.
  2. Names are governed by rules and recommendations.
  3. The names are easy to remember compared to polynomials.
  4. These names are self-explanatory.
  5. The names are in Latin which is a dead language not used in any country, so there is no controversy.

 

TAXONOMIC HIERARCHY

Introduction

The term Taxonomy was coined by Augustin Pyramus de Candolle. Taxonomy is the science of classification of organisms. Classification of organisms is done by Biologists based on evolutionary relationships and shared features among the organisms.

The fundamental unit of life on Earth is refers to as the species. The species is a population or series of populations whose members are able to interbreed freely under natural conditions and who do not breed with other species.

Closely related species are grouped as genus (pl. genera); while closely related genera are grouped as family and so on. This type of grouping makes up the classification hierarchy. The genus and species names are always either italicized or underlined, with the genus name Capitalized and the species name in lower case.

Species are grouped into more comprehensive taxa, these taxa are grouped into larger taxa so that the classification is a hierarchy of a system of units that increase from first level to the next higher level.

Taxonomic hierarchy

Taxonomic Hierarchy or Linnaean hierarchy categories are introduced by Linnaeus. It is defined as arrangement of categories in a decreasing or increasing order from kingdom level to species level and vice versa. Kingdom is the highest rank given in the hierarchy then the levels division, class, order, family, genus and species follow. Species is the lowest rank given in the Hierarchy.

The hierarchy has two categories namely, obligate (main) and intermediate (intra).

  • In obligate category, hierarchy is followed strictly. Here the levels range from kingdom to species.
  • In intermediate category, hierarchy is not followed strictly. The levels are added in between the list such as sub-division, super-family, super-class, sub-order, sub-species and so on.

The following are seven main or obligate categories used in any plan of classification. They are known as the supra-specific groups.

1. Kingdom

2. Division

3. Class

4. Order

5. Family

6. Genus

7. Species

Species: Group of organisms which are similar in form, shape and reproductive features are called species.  This similarity is important so as to produce fertile offsprings. Offsprings are sterile when a hybrid is produced. The level species is followed by subspecies, clines and demes. These categories are inferior when compared to species.

Genus: Genus is a group of related species. Some genera may have only one species (Monotypic) whereas some may have more than one species (polytypic).

Family: Family is the collection of related genera.

Order: One or more than one related families form an order.

Class: One or more than one related orders form a class.

Division: Division is the term used for plants while its synonym phylum is used for animals. It is a collection of related classes.

Kingdom: Kingdom is the uppermost taxonomic category. For example all the plants are included in Kingdom Plantae. Taxon is the unit of classification that denotes group of organisms based on observable features.

Under species we have other groups termed as infra specific groups. The following is the list of intermediate or infra specific groups,

1. Species

2. Subspecies

3. Clines

4. Demes

Various methods used to recognize and categorize organisms are called as Taxonomic aids. Identification of organisms is a tiresome process. Taxonomic keys are used for identification of organisms. Taxonomic key is a long table of statements with different features to recognize the organisms. The features which are related to a particular organism are chosen and then the organism is grouped into the relevant category.

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