Taxonomic Hierarchy and Taxonomic Categories, Practice Problems and FAQs

We live on Earth along with such a huge number of living organisms that it is hard to contemplate. Well, taxonomy came along to rescue us and made it easier for us to study about all organisms in an organised way. Taxonomy is a branch of science that deals with identification, classification and nomenclature of organisms. Classification is an integral part of taxonomy which deals with the grouping or categorisation of organisms.

Well, have you ever thought about how this grouping is done? Which groups do these organisms belong to? The classification is well executed in multiple steps and each step represents rank or category. Let's study these categories in detail.

Table of contents

• Taxonomic hierarchy
• Formation of taxonomic categories
• Taxonomic categories
• Practice Problems
• FAQs

Taxonomic hierarchy

Any category or rank in a taxonomic hierarchy is known as taxon. These categories are also known as taxonomic categories and all the categories combine to form a taxonomic hierarchy. Arrangement of taxonomic groups in a definite order i.e. from highest category to lowest category is known as taxonomic hierarchy.

Formation of taxonomic categories

All the plants and animals are classified into common categories or taxon as per the characteristics of an organism. It is proposed by Linnaeus and also known as the Linnaean hierarchy. Initially, Linnaeus proposed five categories as class, order, genus, species, and variety.

Fig: Linnaean hierarchy

Formation of seven categories

‘Variety’ was discarded and three new categories were added. The lowest category is species and the highest category is the kingdom in both plants and animals in the present hierarchy. The following taxonomic hierarchy with seven obligate categories is used at present:

• Kingdom 
• Division
• Sub phylum
• Class
• Order 
• Family 
• Genus
• Species

Fig: Taxonomic hierarchy

Subcategories and super categories

Discovery of new organisms made it difficult to accommodate all organisms in the taxonomic hierarchy. To add more precision to the taxonomic position of organisms various subcategories and super categories were added. They are also called intermediate categories. 

• Subkingdom
• Subphylum or super division
• Subdivision
• Subclass or superclass
• Suborder or superorder
• Subspecies, tribes, variety etc.

Taxonomic categories

The different taxonomic categories are explained below: 

Fig: Taxonomic hierarchy

Species

It is the lowest category in the taxonomic hierarchy. It constitutes a group of organisms with similar characteristics. Organisms which are genetically distinct and reproductively isolated are categorised under single species. Species name is the second part of the scientific name designated for an organism. For example, the scientific name of mango is Mangifera indica where indica is the name of the species.

Fig: Mangifera indica (Mango)

A single genus may have multiple species which represent different organisms but may have similar morphological characteristics. For example, Panthera leo (lion) and Panthera tigris (tiger) belong to the same genus Panthera but different species, leo and tigris respectively.

Fig: Genus with two different species

Subgroups of species include subspecies or varieties which include organisms with certain distinctive characteristics.

Sibling species

Species which have a high degree of morphological similarities (difficult to differentiate from one another) but cannot interbreed are known as sibling species. For example, Drosophila pseudoobscura and Drosophila persimilis.

Allopatric species

Species formed as a result of geographical isolation are known as allopatric species. Examples include Darwin’s finches. 

Sympatric species

Species formed as a result of reproductive isolation without geographical barriers are known as sympatric species. Examples include, apple maggot, the insect which lays its eggs inside the apple.

Genus

It constitutes a group of related species. The organisms under one genus show close resemblance and hence indicate common ancestry. A genus may have one species (monotypic) or multiple species (polytypic). Species name is the first part of the scientific name designated for an organism. For example, the scientific name of mango is Mangifera indica where Mangifera is the name of the genus of mango.

Family

It constitutes groups of related genera. Genera under one family show more similarities as compared to genera of other families. It is done on the basis of reproductive and vegetative features in plants. Suffix for family name is done as follows:

Plants

Suffix - aceae is used; for example, the family Solanaceae includes genera Atropa, Datura, Petunia etc.

Fig: Family Solanaceae

Animals 

Suffix- idae is used; for example, family Felidae includes animals of genus Panthera (lions, tigers etc.) and genus Felis (cats). 

Fig: Family Felidae 

Order

It constitutes a group of families which resemble each other in a few characteristics. Similarities in characteristics are less in number as compared to the lower taxonomic categories. Suffix for order name is done as follows:

Plants

Suffix- ales is used; For example, Polymoniales is the order constituting families like Convolvulaceae and Solanaceae on the basis of floral characteristics.

Animals

Do not possess special suffixes. Carnivora is the animal order including the family Felidae and Canidae.

Fig: Order Carnivora

Class

It constitutes groups of order related to each other. 

Suffix for class is done as follows:

Plants

Suffix - phyceae, opsida and ae are used. For example, class dicotyledonae include orders like Ranales, Parietales, Geraniales, Rosales etc. 

Animals 

Do not possess special suffixes. For example, class Mammalia includes animals of order Primata, Carnivora, Rodentia etc.

Super class 

It is a taxonomic category present below phylum and above class. For example, super class Pisces include class Chondrichthyes (cartilaginous fishes) and Osteichthyes (bony fishes). 

Fig: Super class Pisces

Subphylum or Subdivision

It constitutes related classes. Subphylum is a taxonomic category present below phylum in animals and subdivision is a taxonomic category present below division in plants. 

Suffix for subdivision in plants 

In plants ‘ae’ is commonly used. For example, subdivision angiospermae possess classes Monocotyledonae and Dicotyledonae. 

Suffix for subphylum in animals

Do not possess special suffixes. For example, subphylum Vertebrata include divisions like Agantha and Gnathostomata. 

Fig: Subphylum Vertebrata

Phylum or Division

It constitutes groups of various classes related to each other. Phylum is the category used in the taxonomic hierarchy of animals and division is the category used in taxonomic hierarchy in plants. Suffix for order name is done as follows:

Plants

Division - phyta, for example, division Thallophyta includes the following classes:

• Class Rhodophyceae (red algae)
• Class Phaeophyceae (brown algae)
• Class Chlorophyceae (green algae)

Fig: Examples of division Thallophyta

Animals 

Do not possess special suffixes. For example, phylum Chordata includes the following classes:

• Class Cyclostomata
• Class Osteichthyes
• Class Chondrichthyes
• Class Reptilia
• Class Amphibia
• Class Aves
• Class Mammalia

Fig: Examples of phylum Chordata

Kingdom

It is the highest category in the taxonomic hierarchy. It includes groups of organisms with common characteristics that distinguish them from other organisms. For example, kingdom Animalia includes all the animals and kingdom Plantae includes all plants. 

Five kingdom classification

Five kingdom classification that classifies all existing organisms into five kingdoms was proposed by R.H. Whittaker. Five kingdoms as per R.H. Whittaker are as follows:

• Monera - Unicellular prokaryotes. Examples include bacteria, cyanobacteria etc.
• Protista - Unicellular eukaryotes. Examples include Amoeba, Hydra etc.
• Mycota (Fungi) - Multicellular eukaryotic saprophytes. Examples include Puccinia, mushroom etc.
• Plantae - Multicellular eukaryotic producers. Examples include mango tree, orangetree etc.
• Animalia - Multicellular eukaryotic consumers. Examples include lion, tiger etc.

Examples of taxonomic categories of common organisms

Practice Problems

Q 1. Which of the following statements is incorrect?

a. Kingdom is considered as the highest category of the taxonomic hierarchy
b. Sub phylum in animals do not possess suffixes
c. A group of related orders comprises family
d. Order represents a group of families having some similar characteristics

Answer: A family represents a group of related genera. When compared to genera from different families, genera within one family show higher similarities. Animals of the genus Panthera (lions, tigers, etc.) and genus Felis, for example, are members of the Felidae family (cats). Hence option c is the answer. 

Q 2. Assertion: Sympatric species are formed as a result of reproductive isolation.
Reason: Species develop into separate species without any hindrance of geographical barriers.

a. Both assertion and reason are true, and reason is the correct explanation of the assertion.
b. Both assertion and reason are true, but reason is not the correct explanation of the assertion.
c. Assertion is true, reason is false.
d. Both assertion and reason are true.

Answer: Sympatric species are formed due to reproductive isolation. New species arise from the ancestral species, the new species formed are genetically different and thus are unable to mate with the ancestral species. This makes the new species reproductively isolated. Though the geographical barriers are absent, the species are unable to mate in the population. Examples include, apple maggot, the insect which lays its eggs inside the apple. Hence, option b is correct.

Q 3. Match the following.

a.  A - II, B - IV, C - I, D - III, E - VI, F - V
b. A - II, B - III, C - I, D - VI, E - IV, F - V
c. A - III, B - II, C - IV, D - I, E - VI, F - V
d. A - I, B - III, C - IV, D - V, E - II, F - VI

Answer: Mangifera indica is the scientific name of Mango. It belongs to the genus Mangifera and species indica. Mango belongs to the family Anacardiaceae, order Sapindales, class Dicotyledonae, and phylum Angiospermae. Hence, option a is correct.

Q 4. State the difference between taxonomic hierarchy and taxonomic category.
Answer : Classification involves a series of steps, each of which reflects a rank or category. It is named taxonomic category because it is a part of the larger taxonomic arrangement. Taxonomic hierarchy is made up of all of the categories. Taxonomic hierarchy is the arrangement of taxonomic groups or categories in a definite order, from highest to lowest category.

Q 5. State the difference between genus and species.
Answer: The differences between genus and species are as follows:

FAQs

Q 1. Why is species a basic taxonomic category?
Answer: A species is made up of one or more individuals who are more similar to one another than individuals from other species. Members of a species are reproductively isolated from members of other species and can freely interbreed. These characteristics make species a basic taxonomic category.

Q 2. Write down the name of the organism with the longest scientific name.
Answer: Parastratiosphecomyia stratiosphecomyioides with 42 characters, this small Indian fly has the longest scientific name of any species. 

Fig: Parastratiosphecomyia stratiosphecomyioides

Q 3. Why are taxonomy levels always changing?
Answer: Earth has a rich biodiversity and many species are yet to be discovered. So to classify these new undiscovered species into convenient categories, based on their distinctive characteristics, the available classification systems need to change every now and then. So that the newly discovered species can be accommodated conveniently.

Q 4. Why is taxonomy considered as a science without data?
Answer: In taxonomy there are millions of organisms. It is not easy to identify them and name them. This procedure requires scientific observations with care. So in simple words, we can say taxonomy scientifically deals with identification, classification and naming of the organisms.

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