Table of Contents

Taxonomy and Systematics

[List of Systems of Plant Taxonomy](#List of Systems of Plant Taxonomy)

Modern Taxonomic Advancements

Importance of Plant Taxonomy

[Frequently Asked Questions](#Frequently Asked Questions)

The term “taxonomy” is derived from the words “taxis” (arrangement) and “nomos” (laws). Plant taxonomy involves the categorization of plants according to predetermined regulations. This term was first used by the Swiss botanist A. P. de Candolle in his book “Théorie élémentaire de la botanique”.

Two plants are related taxonomically if they have descended from a recent common ancestor and share similar characteristics, such as the ability to store carbohydrates in a particular type of molecule.

Plant Taxonomy is the branch of botany that focuses on the characterization, identification, classification, and nomenclature of plants, based on their similarities and differences.

The goals of plant taxonomy are:

1. To classify plants into groups based on their similarities and differences.

2. To provide a universal naming system that can be used to identify plants.

3. To understand the evolutionary relationships between different plants.

4. To aid in the conservation of plant species.

5. Identification: Identify the unknown species by recognizing its essential characteristics and comparing it to already existing species.

6. Characterization: Describing all the characteristics of the newly identified species.

7. Classification: Organizing known species into distinct groups based on shared characteristics and differences.

4. Nomenclature: Assigning scientific names according to established conventions.

Taxonomy and Systematics

The word systematics comes from the word ‘systema’, meaning the systematic arrangement of the organisms. It takes into consideration the evolutionary relationship between the organisms and studies biological diversity. Plant systematics specifically deals with the interrelation between plants and their evolutionary descent, and organises the information into a classification.

Organisms are classified based on similarities, closeness or relationship between them. This phylogenetic taxonomy displays the line of descent of different organisms and how they are related. Through the similarities among individuals, it is evident that they may have evolved from a common ancestor, thus showing the evolutionary pathway of modern living organisms. Closely related organisms are grouped together, sharing a common gene pool.

The different taxonomic categories in their hierarchical order are:

1. Kingdom
2. Phylum
3. Class
4. Order
5. Family
6. Genus
7. Species

Kingdom

Phylum

Class

Order

Family

Genus

Species

The number of common characteristics decreases as we move from species to the kingdom, where species have fundamental similarities and organisms in the same kingdom have the least common features.

List of Systems of Plant Taxonomy

1. Bentham & Hooker System
2. Engler & Prantl System
3. Cronquist System
4. Thorne System
5. Takhtajan System
6. Dahlgren System
7. Reveal System

The earliest system of classification took into account only a few vegetative characteristics. However, modern taxonomic studies are much more detailed, taking into account various morphological, cellular, and molecular characteristics, such as cellular and reproductive features, mode of nutrition, habitat, evolutionary relationships, etc., in addition to morphological features.

Here is a list of the three main systems of plant taxonomy:

1. Linnaean Taxonomy

2. Phylogenetic Taxonomy

3. Evolutionary Taxonomy

4. Artificial Classification System

2. Natural System of Classification

3. Phylogenetic System of Classification

1. Artificial Systems: Early artificial systems attempted to classify organisms based on a few observable characteristics.

The first attempt to organize living organisms was an important milestone in the history of biological classification, however, it had some drawbacks. It failed to take into account morphological details and the evolutionary relationship between species, and gave equal importance to vegetative and sexual characters, though this is not accurate as vegetative characters are greatly affected by the environment. As a result, closely related species were kept apart.

More than 2000 years ago, Aristotle classified plants into three categories based on morphological characteristics: herbs, shrubs, and trees.

Theophrastus is known as the “Father of Botany” due to his book “Historia Plantarum or Enquiry into Plants”, in which he attempted to classify plants based on their reproductive methods and uses.

Carl Linnaeus is known as the “Father of Modern Taxonomy” and is credited for introducing the hierarchical system of classification in his book “Systema Naturae” (1735), which divided the natural world into the plant kingdom, the animal kingdom and mineral kingdom.

He understood the importance of floral characters and classified plants based on the number of stamens present in them, which is commonly known as the Sexual System of classification.

In “Species Plantarum” (1753), Linnaeus described around 7,300 plant species, and divided the plant kingdom into 24 classes based on the structure, union, length and the number of stamens, such as Monoandria (1 stamen), Diandria (2 stamens), Polyandria (more than 12 stamens), Monoadelphia (stamens united in a single bundle), Monoecia, Dioecia, Polygamia (polygamous plants), Cryptogamia (flowerless plants), etc. He kept on adding new work to his publications.

He gave the Binomial Nomenclature System in his book “Philosophia Botanica”. This system is called binomial because each name has two components, a genus name and a species name, for example Solanum melongena (brinjal) and Solanum tuberosum (potato) have the same genus but different species names.

2. Natural Systems: This system of classification was based on the natural similarities of vegetative and floral characters among the organisms. It took into account various external and internal features such as the anatomy of a cell, types of embryo, and phytochemistry, considering more characters than previous systems.

The most important natural system of classification of flowering plants was the Bentham and Hooker system of classification, which divided plants into two categories: Cryptogams (non-flowering plants) and Phanerogams (flowering plants).

In the Bentham and Hooker classification system, 97,205 species of seed plants were classified into 7569 genera and 202 families. The flowering plants were further classified into three classes namely Dicotyledon, Gymnosperm and Monocotyledon.

The Bentham and Hooker system of classification was published in the book “Genera Plantarum” over the course of three issues from 1862 to 1883.

It failed to accurately identify the phylogenetic relationships between different groups of plants, incorrectly placing gymnosperms between monocotyledons and dicotyledons. However, it did help to determine relationships between the various groups of plants.

3. The Phylogenetic System of Classification: This system is based on evolutionary sequence and genetic relationship. It was developed after Charles Darwin published his theory of evolution, and takes into account not only morphological characteristics found in fossil records, but also genetic constituents. This system has been widely accepted by biologists around the globe, as it states that all organisms belonging to the same taxa have a common ancestor.

Various scientists, such as Engler and Prantl, Hutchinson, Takhtajan, Cronquist, Rolf Dahlgren, and Robert F Thorne, contributed to the phylogenetic system of classification.

The two main phylogenetic systems of classification are:

• Linnaean Taxonomy
• Cladistics

Engler and Prantl System of Classification: In this type of phylogenetic system of classification, floral characters such as a single whorl or no perianth, unisexual flowers pollinated by wind were considered primitive, whereas two whorls in the perianth and bisexual flowers pollinated by insects were considered more complex. Plants were arranged based on the increasing complexity of the flower morphology.

The plant kingdom was divided into 13 divisions:

11 Thallophytes

+ 12th Embryophyta Asiphonogama, i.e. plants having embryos but lacking pollen tubes (bryophytes and pteridophytes)

The 13th Embryophyta Siphonogama, i.e. plants with embryos and pollen tubes (seed plants), are included.

John Hutchinson, a British botanist, proposed the phylogenetic system of classification in his two-volume book, “The Families of Flowering Plants,” which was published in 1926 and 1934. In his classification, Hutchinson divided angiosperms into monocotyledons and dicotyledons.

Dicotyledons were further divided into two divisions: Lignosae (woody plants) and Herbaoae (herbaceous plants).

• Monocots were divided into three divisions based on flower morphology: Calyciflerae (with calyx present), Corolliferae (with petaloid perianth), and Glumiflorae (with perianth absent).

Modern Taxonomic Advances

The development of molecular biology has enabled us to create methods to identify genetic material, allowing us to compare organisms at varying taxonomic levels and overcome the challenges of classifying them even when there is no fossil evidence.

1. Numerical Taxonomy: This method of taxonomy involves the use of computers to analyze all observable characters. Each character is assigned a code and a numerical value. This allows for hundreds of characters to be considered together, each given equal importance.

2. Cytotaxonomy: It utilizes cytological information such as chromosome number, shape, and size to gain an understanding of the taxonomy.

3. Chemotaxonomy: The use of chemical constituents of plants for taxonomic studies is referred to as chemotaxonomy. Chemotaxonomy involves the study of proteins, amino acids, nucleic acids and peptides, starch grains, wax, fat, oil, and phenols.

The Importance of Plant Taxonomy

It provides a comprehensive examination of the various morphological and anatomical features of a plant species.

It organizes all the information of plants into an orderly fashion.

It indicates the phylogenetic relationship between species and its lineage.

Plant taxonomy allows for the identification of an unknown species and its place in the classification by comparing it to known species.

Analysis of genetic constituents can be done through systematics

The binomial nomenclature system is used to scientifically name any species, which helps in providing a uniform name for the species across the globe and avoids any confusion.

It helps to gain an understanding of the biodiversity present at a place

It assists in documenting all the living species identified to date.

Taxonomy is extensively employed in agriculture, medicine, and forestry.

Frequently Asked Questions

How many families are there in Bentham and Hooker’s classification?

There are 202 families in the Bentham and Hooker system of classification, Dicotyledons (165), Gymnosperms (3), and Monocotyledons (34).

What are the Disadvantages of Phylogenetic Classification?

The only disadvantage of the phylogenetic system of classification is that it only talks about organisms with a common ancestor.

What is the Role of Palynology in Taxonomy?

Palynology is essential for studying taxonomy and evolution, and it can be used to identify phylogenetic connections between extant and fossilised plant species.

What is the scientific name of a plant?

The scientific name of the plant is written according to the taxonomy in a binomial name; the genus name is written first and the specific epithet is written second, both of which are written in italicised letters or otherwise underlined.