An Introduction to Plant Taxonomy

Introduction to Plant Taxonomy

Systematics

Systematics refers to the study and classification of organisms for the determination of the evolutionary relationship of organisms. It includes classification, naming, cladistics, and phylogenetics.

OR

It is also defined as the study of all kinds and diversity of all organisms and any or all relationships between them.

Taxonomy and systematics are both used to identify, classify organisms. Taxonomy comes under systematics where it involves the identification, naming and classifications of the organism. But Systematics involves the evolutionary relationships of the organisms along with the taxonomy.

Taxonomy

• The term taxonomy was first used by a French botanist called A.P. De Candolle.
• In Greek Taxonomy means Arrangement by rules.

Taxonomy is defined as the branch of science dealing with the study of classification including its basic principles, rules, and procedures. It can also be defined as principles of classification of organisms.

OR

A branch of botany that deals with the study of identification, naming & classification of plants in a systematic manner is called plant taxonomy.

Objectives and Goals of Plant Systematics

Objectives of Plant Systematics

• To prepare a scheme of classification that provides a phenetic, natural or phylogenetic relationship among taxa.
• To establish a suitable method for the identification nomenclature and description of taxa.
• To provide an inventory of plant taxa that suites local regional and continental needs.
• To create an understanding of the evolutionary process.
• To train students of biology with regard to the diversity of organisms and their relationship with other biological branches.

Goals of Plant Systematics:

• To acquire fundamental values of plant systematics.
• To know about the basic concepts and principles of plant systematics.
• To be aware of the importance of taxonomic relationships and plant systematics.
• To develop a knowledge of the applicability of plant systematic studies. 

Also Read: Introduction to Algae and Historical Developments in Algology

Components of Plant Taxonomy 

1. Identification
2. Naming
3. Classification

Identification

In the study of taxonomy identification of plants is done by comparing the characteristics of unknown plants with the characteristics of known plants.

Naming

a) Common name:  The common name varies from place to place or region to region/country to country. Common names lead to confusion. 

Examples: Mango, Jackfruit, Guava, Coconut, areca nut, teak etc.

b) Scientific name: The naming of a plant in a scientific manner or method is called the scientific name or botanical name. 

• Each scientific name or botanical name consists of two Latin words. 
• The first Latin word indicates a Generic name and the second Latin word indicates a specific name. Examples:  Solanum melongena (brinjal), Solanum tuberosum (potato), Ficus bengalensis (Fig), Agave mexicana, Agave americana etc.
• The generic name starts with a capital letter & the specific name starts with a small letter.
• In the scientific name, the genera or species always denotes the name of the discoverer or the name of the place or special character of that plant.

Binomial nomenclature:

Binomial nomenclature was first introduced by ‘Carl Linnaeus’ a Swedish botanist. According to ‘Carl Linnaeus, each plant has two names, one is a generic name & the other is a species name. This is called Binomial Nomenclature.

Classification

This is the third component of taxonomy. Classification is assigning a plant to a particular division or class or order or family.

Classification Of Angiosperms

Angiosperms are also known as Flower Bearing Plants. Angiosperms are classified into three types:

1. Artificial system of classification
2. Natural system of classification
3. Phylogenetic of classification

1. Artificial System of Classification :

• The artificial system of classification is the first type of classification. This classification was introduced by the famous Sweden botanist Carl von Linneaus (1707-1762). He is known as the ‘Father of Taxonomy’.
• This classification was based on many superficial morphological characters. He divided angiosperms into five groups: herbs, shrubs, trees, and climbers.

Carolus Linnaeus classified the plant kingdom into 24 classes based on the characteristics of flowers, especially the number and behaviour of stamens.

List of 24 Classes of Artificial System of Classification 

Artificial System of Classification by Carolus Linneaus listed below, all 24 Classes with examples:

• Class 1: Monandria – Single stamen
  Example:  Lemna
• Class 2: Diandria – Two stamens
  Example: Salvia
• Class 3: Triandria -Three stamens
  Example:  Iris
• Class 4: Tetrandia – Four stamens
  Example: Mentha 
• Class 5: Pentandria – Five stamens  
  Example:  Primula
• Class 6: Hexandria – Six stamens 
  Example: Aesculus 
• Class 7: Heptandria – Seven stamens
  Example:  Aesculus
• Class 8: Octandria – Eight stamens
  Example: Fagopyrum
• Class 9: Ennenandria – Nine stamens 
  Example: Rheum
• Class 10: Docandria -Ten stamens 
  Example:  Acer
• Class 11: Dodecandria– 11-19 stamens
  Example:  Calla
• Class 12: Iscosandria – 12 or more attached to the calyx 
  Example: Rosa 
• Class 13: Polyandria – More than 19 stamens, attached to the receptacle 
  Example: Tilia
• Class 14: Didynamia– Stamens  didynamous (two larger)
  Example: Ocimum 
• Class 15: Tetradynamia – Stamens tetradynamous ( four larger)
  Example: Brassica 
• Class 16: Monoadelphia – Stamens in one bundle 
  Example: China rose
• Class 17: Diadelphia– stamens in two bundle
  Example: Soybean
• Class 18: Polyadelphia – Stamens remain in several bundles 
  Example: Citrus
• Class 19: Syngenesia -Anthers are united in the stamens 
  Example: Sunflower 
• Class 20: Gynandria– Stamens attached with the pistil
  Example: Calotrophis 
• Class 21: Monoecia 
  – Plants are monoecious i.e.staminate and pistillate flowers remain in the same plants.
  Example: Bitter gourd, bottle gourd
• Class 22: Dioecia 
  – Plants are dioecious i.e. staminate and pistillate flowers remain in different plants 
  Example: Ribbed gourd
• Class 23: Polygamia 
  – Plants polygamous i.e. plants having hermaphrodite and unisexual flowers in the same plant.
  Example: Papaya, sunflower
• Class 24: Cryptogamous
  – Flowers are concealed.
  Example: Algae,fungi,mosses

Disadvantages of Artificial system of classification:

1. It does not give any information regarding the natural relationship or phylogeny of taxa.
2. It is simply based on superficial and easily recognisable characteristics like habitat, habit and sex of the plants.
3. This system keeps dissimilar organisms in one group and similar organisms in different groups.

2. Natural system of classification

1. This is the second type of classification. The Natural System of Classification was proposed by the famous English botanist Benthem & Hooker (1862-1883). 
2. This classification was based on the characters of the root system, shoot system, leaves, Fruits & flowers & seeds.
3. Bentham and Hooker divided the plant kingdom into two divisions : 
   • Cryptogamia (non-flowering plants) 
   • Phanerogamia (flowering plants)
4. The division Phanerogamia is divided into three classes:
   1. Dicotyledon
   2. Gymnosperms
   3. Monocotyledon

Class: Dicotyledon

This group includes angiosperms in which the seed bears two cotyledons and leaves exhibit reticulate venation. It is divided into three subclasses- Polypetalae, Gamopetale, and Monochlamydeae.

Subclass: Polypetalae

The flowers contain distinct non-essential whorls calyx and corolla. In the corolla petals are free. This subclass includes three series Thalamiflorae, Disciflorae and Calyciflorae.

1. Series Thalamiflorae: Thalamus drum-shaped, many stamens in the androecium, Flower is hypogynous. Example: Michellachampara
2. Series Disciflorae: Thalamus expanded and disc present. Hypogynous flowers with a cushion-like disc around or below the ovary. Example: Glycosmis Arborea
3. Series Calyciflorae: Flowers epigynous or perigynous. Thalamus is in the form of a cup. Example: Senna sophera

Subclass: Gamopetalae 

Flowers with distinct calyx and corolla and the corolla petals are fused. This subclass includes the following three series:

1. Series Inferae: Flowers with an inferior ovary. Example: Mikania Cordata
2. Series Heteromerae: Flowers with superior ovary, numbers of carpels are more than two. Example: Rhododendron arboreum
3. Series Bicarpellatae: Flowers with superior ovary, number of carpels are two.
   Example: Leucas Aspera

Subclass: Monochlamydeae

The flowers are with only one non-essential whorl (perianth) ‘or absence of non-essential whorls. It includes the following 8 series:

1. Series 1 : Curvembryae:
   Usually single ovule, embryo coiled around the endosperm.
   Example:Persicaria hydropiper
2. Series 2:Multi ovulate Aquatica:
   Aquatic plants with syncarpous ovary and many ovules
   Example: Lacis Monadelpha
3. Series 3: Multiovulate Terrestris:
   Terrestrial plants with syncarpous ovary and many  more ovules
   Example: Aristolochia Indica 
4. Series 4: Microembryae:
   Only one ovule, small, tiny embryo endospermic seed
   Example: Piper nigrum
5. Series 5: Daphnales:
   Only one ovule and contain a single ovule.
6. Series 6: Achlamydosporae:
   Ovary inferior, 1 to 3 ovules- unilocular
   Example:Santalum album
7. Series 7: Unisexuales:
   Flower unisexual, perianth usually absent
8. Series 8: Ordines Anomali: (Anomalous families)
   Plants with uncertain systematic position but closer to unisexuales
   Example:Ceratophyllumdemersum

3. Phylogenetic System Of Classification :

This is the third type of classification. This classification was proposed by the famous German botanist Engler & Karl Prantl (1844-1938). This classification was based on many evolutionary characters. They divided the plant kingdom into 13 Divisions mentioned as below: 

• Division 1: Schizophyta
• Division 2: Myxothallophyta
• Division 3: Flagellate 
• Division 4: Dinoflagellatae
• Division 5: Bacillariophyceae
• Division 6: Conjugatae
• Division 7: Chlorophyceae
• Division 8: Charophyta
• Division 9: Phaeophyceae
• Division 10: Rhodophyceae
• Division 11: Eumycetes
• Division 12: Embryophyta Asiphonogama
• Division 13: Embryophyta Siphonogama

To Be Continued…