Taxonomy Examples and Definition

Can you name all the roadside plants that grow in your locality? Do you know the names of all the birds that come and sit on the tree beside your home? Has it ever happened that you saw a bird that you have never seen before and wondered what type of bird is this? Everytime I come across a plant or animal that I do not know of, I get this tingly feeling that maybe I discovered a new species! But, sadly that has never been the truth because someone or the other has burst my bubble of hope by enlightening me with the name of the organism, and proven how inadequate is my knowledge of the living world.

But, it’s not just me or you. The human race as a whole knows very little about the living world. Out of the millions of species inhabiting the earth, only 1.7-1.8 millions have been discovered so far and around 15,000 species are discovered every year. So a huge amount of work is yet to be done. But identifying, classifying and naming millions of species is not an easy task and requires a proper system.

Have you ever visited libraries? If yes, you might have seen different sections inside the library. There will be different sections for different languages, and also different sections for kids and adults, literature and science, novels and short stories, poems and stories etc. Sometimes the books are arranged according to the names of the authors. These kinds of arrangements make the process of searching for the books easier. So perfect arrangement and classification of any kind of stuff can make it easier to collect. This is applicable in the case of any kind of subject.

Fig: Library

This method is also adapted in the classification of organisms. Do you know what the total number of organisms on Earth is? It is estimated that 8.7 million different forms of life are present on the earth. So studying about each organism is not possible. The only way to get to know more about them is to categorise them into different groups, just like we did in the library. Do you think it is possible? It is done through a branch of biology called taxonomy. Now we are going to discuss more about taxonomy in this article.

Taxonomy

The branch of science that deals with the grouping of organisms into individual groups is known as taxonomy. ‘Taxis’ is a Greek word which means arrangement and nomos is also a Greek word which means law. The categories for grouping organisms are termed as taxa (singular. taxon). German biologist Adolf Meyer was the one who introduced the term ‘taxon’ for the first time.

Fig: Classification of organisms

French taxonomist A. P. de Candolle proposed the rules and technical procedures used for constructing classification in the year 1813. He used it for classifying plants for the first time and then later it was adopted for animal classification. Taxonomie (french word) was the first word he used for taxonomy.

Fig: A. P. de Candolle

Taxonomy is mainly based on the gross morphological features of the organisms. But other information available from other branches such as anatomy, histology, physiology, cytology, genetics, molecular biology etc are also applied to classify the organisms. Hence taxonomy is a multidisciplinary, synthetic and dynamic branch of biological science. The major purpose of taxonomy is to reveal the ancestry and evolutionary relationship between the organisms.

Systematics

Systematics is the branch of biology that deals with the study of diversity in the living world and the comparative and evolutionary relationships between organisms by comparing their anatomical, biochemical, physiological and ecological characteristics. Classical systematics involved the schemes to identify and classify the organism on the basis of their morphological features. Biosystematics or new systematics which is mainly based on the phylogenetic relationships between organisms takes the characters related to morphological, cytological, physiological, biochemical, ecological, genetics, etc., into consideration. Systematics requires modern taxonomic procedures which can be divided into several steps.

Steps of modern taxonomy

The steps of modern taxonomy are as follows:

Characterisation and identification
Classification
Nomenclature

Fig: Steps of modern taxonomy

Characterisation and identification

This step is to identify and characterise an unknown organism by comparing it with a known organism. It is done with the help of taxonomical aids.

The techniques, procedures and information stored to study and then identify an organism are called Taxonomic aids. The organisms identified through these collections of samples or preserved creatures can be then classified. The samples collected for taxonomic aids can be dead or alive. Different types of taxonomic aids are as follows:

Herbarium
Museum
Botanical gardens
Zoological parks
Keys
Monographs
Manuals
Flora
Catalogues and publications

Fig: Examples of taxonomical aids

Classification

Arrangement of organisms into groups or categories on the basis of their affinities or relationships is known as classification.

Nomenclature

The method of providing distinct and proper names to organisms as per established universal practices and rules are called nomenclature. Through this, organisms can be easily recognised and differentiated from others. The given name is known as the scientific name and it ensures that only one name is given to an organism and description of the organism should help the other people to arrive at the same name in any part of the world. There are different types of nomenclature systems such as:

Monomial Nomenclature
Binomial Nomenclature
Trinomial Nomenclature
Polynomial Nomenclature

Among these binomial nomenclature is the most widely accepted type of nomenclature. This system was given by Carolus Linnaeus. In the binomial nomenclature, two terms are used to denote a species of living organism and they are the generic name and specific epithet. For example the scientific name of mango tree is Mangifera indica Linn. Here the Mangifera is genus name and indica is species name. In some organisms, the name of the scientist who described the organism will be also given after the specific epithet. So here it is the abbreviation of Linnaeus.

Fig: Mango tree

So if we get an unknown organism we can then use these three steps to identify the organism and classify it under a particular taxa. First the morphological and all other characters are described and similarities and dissimilarities are compared with already known organisms. Now the Characterisation and identification is done. Next we can place the organism under a particular taxa or category through the step of classification. The last step is to give the proper scientific name to the organism.

Taxonomic hierarchy

While categorising the organism, the relationship between each organism will make them get added in a particular group or category. Hence the organisms with similar characteristics will get into the same group., which means they closely resemble each other. Each category is called a taxon and these taxa are arranged in different levels.

The framework by which taxonomic groups or taxons are arranged in definite order, from lower to higher categories or in progressively complex categories is called taxonomic hierarchy. It is also called the Linnaean hierarchy because it was first proposed by Linnaeus. He first used only five categories and they were the class, order, genus, species and variety. The last one was discarded and three more added in its place, so that now there are seven obligate categories as follows:

Kingdom
Division
Phylum
Class
Order
Family
Genus
Species

Fig: Taxonomic hierarchy

Above the Kingdom there is one more taxonomic category, which is the domain. Categories in the hierarchy are thus in ascending order. Hence as we go from the lowest rank i.e., species towards the Kingdom the number of similar characters decreases.

Modern trends in taxonomy

More evidence is needed from different fields of biology for the identification, description, classification and naming of organisms. In the absence of fossil evidences, classification based on evolutionary relationships is difficult. In such cases, some of the following branches of taxonomy provide additional criteria and methodologies for classification:

Chemotaxonomy
Cytotaxonomy
Numerical taxonomy
Molecular taxonomy

These emerged after the second half of the 20th century, because taxonomy was initially based on the morphological and anatomical features and was known as the classical taxonomy. Now we will discuss more about the modern trends in taxonomy.

Chemotaxonomy

The branch of taxonomy based on the study of similarities of biomolecules present in the organisms is called chemotaxonomy. It is also known as biochemical taxonomy. The significance of chemotaxonomy in elucidating the phylogeny of organisms is high. The chemicals that are studied in chemotaxonomy are proteins, amino acids, nucleic acids, peptides etc.

Fig: Protein and amino acids

Cytotaxonomy

The branch of taxonomy based on the study of the cell or more specifically the study of chromosomes which differentiates different organisms is called cytotaxonomy. The characteristics of chromosomes used in cytotaxonomy are as follows:

Chromosome number
Chromosome size
Chromosome morphology
Chromosome behaviour at meiosis

For example the chromosome number in humans is 46 and for Ophioglossum it is 1260.

Fig: Different chromosomes in human

Numerical taxonomy

The branch of taxonomy based on the numerical evaluation of the similarities between different groups of organisms is called numerical taxonomy. It is also known as mathematical taxonomy, taxometrics or phenetics. This evaluates the data derived from the phenotypes of organisms. Adanson proposed the idea of a phenetic system of classification.

Molecular taxonomy

The branch of taxonomy that deals with the molecular similarities between the organisms is called molecular taxonomy. It is a recently emerged branch of taxonomy. It utilises the data from the DNA present in nucleus, chloroplast and mitochondria and elucidates the phylogenetic relationship between the organisms. Gene sequences are also used in molecular taxonomic studies and they are obtained from protein coding genes, ribosomal RNA etc.

Fig: DNA

Contribution of taxonomists

Aristotle was the one who first classified the organisms into two groups; plants and animals. Theophrastus was the student of aristotle. He mentioned 500 plants and their uses in his book called Historia Plantarum.

Fig: Aristotle

In the mediaeval ages all taxonomists followed the Aristotelian system with some additions. Microbial organisms were classified during this period, because the microscope was discovered. Scholars like Procopius, Thomas Aquinas, Pepagomenos and Timotheos of Gaza made more advanced studies in the classification of organisms.

Andrea Cesalpino was called as the first taxonomist, who described more than 1500 plant species. The two plant families, Asteraceae and Brassicaceae found by Cesalpino are still in use. John Ray was another taxonomist who described 18000 plant species and published in his book, Methodus Plantarum Nova. The works of Joseph Pitton de Tournefort directly influenced Carl Linnaeus to get into taxonomy.

Carl Linnaeus is known as the father of taxonomy. He described plants in two of his publications; Systema Naturae and Species Plantarum. The standard binomial system of nomenclature of organisms used by Linnaues is still followed by the modern taxonomists.

Fig: Carolus Linnaeus

Benefits of taxonomy

There are many benefits for taxonomic studies. Some of them are as follows:

Categorisation of organisms for ease of study.
Compares similarities and differences between organisms.
Shows evolutionary relationships between organisms.
The same name is used for an organism worldwide.
Gives us a knowledge of bioresources and their diversity.

Practice Problems

Q1. Which of the following statements are true about taxonomy?

I) Carl Linnaeus is the father of taxonomy.
II) The categories for grouping organisms are termed as taxa.
III) Adolf Meyer proposed the rules and technical procedures used for constructing classification and used it for classifying animals for the first time
IV) Taxonomy is a multidisciplinary, synthetic and dynamic branch of biological science.

I, II, III, IV
I, II
I, II, IV
II, III, IV

Solution: The branch of science that deals with the grouping of organisms into individual groups is known as taxonomy. ‘Taxis’ is a Greek word which means arrangement and nomos is also a Greek word which means law. The categories for grouping organisms are termed as taxa (singular. taxon). German biologist Adolf Meyer was the one who introduced the term ‘taxon’ for the first time. French taxonomist A. P. de Candolle proposed the rules and technical procedures used for constructing classification in the year 1813. He used it for classifying plants for the first time and then later it was adopted for animal classification. Taxonomie (french word) was the first word he used for taxonomy. Classical taxonomy involved classifying organisms based on the gross morphological features of the organisms. But other information available from other branches such as anatomy, histology, physiology, cytology, genetics, molecular biology etc are also applied to classify the organisms. Hence taxonomy is a multidisciplinary, synthetic and dynamic branch of biological science. Hence the correct option is c.

Q2. Cytotaxonomy is the branch of taxonomy which deals with which of the following characters of chromosomes?

Chromosome number and size
Chromosome morphology
Chromosome behaviour at meiosis
All the above

Solution: Classical taxonomy is mainly based on the gross morphological features of the organisms. But other information available from other branches such as anatomy, histology, physiology, cytology, genetics, molecular biology etc are also applied to classify the organisms. According to the branch of biology used in the taxonomic studies, there are different branches of taxonomy: chemotaxonomy, cytotaxonomy, numerical taxonomy and molecular taxonomy. The branch of taxonomy based on the study of the cell or more specifically the study of chromosomes which differentiates different organisms is called cytotaxonomy. The characteristics of chromosomes used in cytotaxonomy are chromosome number, chromosome size, chromosome morphology and chromosome behaviour at meiosis. Hence the correct option is d.

Q3. Assertion: Binomial nomenclature is the most widely accepted type of nomenclature.

Reason: Two terms are used to denote a species of living organism in binomial nomenclature.

Which of the following statements are correct regarding the assertion and reason given above?

Both assertion and reason are correct and reason is the correct explanation of the assertion
Both assertion and reason are correct, but reason is not the correct explanation of assertion.
Assertion is correct and reason is wrong.
Both assertion and reason are wrong.

Solution: Characterisation and identification, classification and nomenclature are the steps of modern taxonomy. The method of providing distinct and proper names to organisms as per established universal practices and rules are called nomenclature. Through this, organisms can be easily recognised and differentiated from others. The given name is known as the scientific name and it ensures that only one name is given to an organism and description of the organism should help the other people at any part of the world to arrive at the same name. There are different types of nomenclature. They are monomial nomenclature, binomial nomenclature, trinomial nomenclature, polynomial nomenclature. Among these binomial nomenclature is the most widely accepted type of nomenclature. This system was given by Carolus Linnaeus. In the binomial nomenclature, two terms are used to denote a species of living organism and they are generic name and specific epithet. Hence the correct option is b.

Q4. What is the difference between chemotaxonomy and molecular taxonomy?

Answer: According to the branch of biology used in the taxonomic studies, there are different branches of taxonomy. Chemotaxonomy and molecular taxonomy are two of the branches. The branch of taxonomy based on the study of similarities of biomolecules present in the organisms is called chemotaxonomy. It is also known as biochemical taxonomy. The significance of chemotaxonomy in elucidating the phylogeny of organisms is high. The chemicals that are studied in chemotaxonomy are proteins, amino acids, nucleic acids, peptides etc. The branch of taxonomy that deals with the molecular similarities between the organisms is called molecular taxonomy. It is a recently emerged branch of taxonomy. It utilises the data from the DNA present in nucleus, chloroplast and mitochondria and elucidates the phylogenetic relationship between the organisms. Gene sequences are also used in molecular taxonomic studies and they are obtained from protein coding genes, ribosomal RNA etc.

FAQs

Q1. What is the difference between systematics, classification and taxonomy?

Answer: Systematics is a broad field of biology which deals with all the aspects of organisms to add them into some kind of order. It studies diversity in the living world and the comparative and evolutionary relationships between organisms by comparing their anatomical, biochemical, physiological and ecological characteristics. Classification and taxonomy are parts of systematics.

Taxonomy includes the study of diversity, grouping, evolutionary relationships among organisms etc. But classification is only involved with adding organisms into different groups on the basis of relationships between each other. Hence, the subjects of classification are organisms and subjects of taxonomy are classifications and the subject of systematics includes all the relevant study of organisms including classification, taxonomy, evolution and nomenclature (naming of organisms).

Q2. What is OTU or operational taxonomic unit?

Answer: The basic unit of numerical taxonomy is called OTU or operational taxonomic unit. It is the lowest taxon studied in the investigation. OTU represents any item, individual or a convenient group used for comparison or analysis.

Q3. What is a rank in the taxonomic hierarchy?

Answer: Ranks are the different levels in taxonomic hierarchy. Taxa or taxonomic groups are the different groups of organisms of a particular rank. Hence the taxonomic groups of the same rank belong to the same category.

Q4. What are the three periods of taxonomy?

Answer: The three periods of taxonomy are related to important events in the classification which are alpha, beta and gamma taxonomy. The term used to refer to the discipline of finding, describing and naming a taxa is alpha taxonomy. The term was introduced by William Bertram Turrill. The arrangement of species in their natural systems of category is called beta taxonomy. The evolutionary sequence, intraspecific variations and the interpretation of organic diversity is done by gama taxonomy.

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