describe any three types of classification briefly
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Answer:
Types of classification - Taxonomy
1. Artificial system of classification 2. Natural system 3. Phylogenetic system of classification 4. Angiosperm phylogeny group (APG) classification
Taxonomic entities are classified in three ways. They are artificial classification, natural classification and phylogenetic classification.
1. Artificial system of classification
Carolus Linnaeus (1707 - 1778) was a great Swedish Botanist and said to be the “Father of Taxonomy.” He outlined an artificial system of classification in “Species Plantarum” in 1753, wherein he listed and described 7,300 species and arranged in 24 classes mostly on the basis of number, union (adhesion and cohesion), length, and distribution of stamens.
2. Natural system
Botanists who came after Linnaeus realised that no single character is more important than the other characters. Accordingly an approach to a natural system of classification sprouted in France. The first scheme of classification based on overall similarities was presented by Antoine Laurent de Jessieu in 1789.
A widely followed natural system of classification considered the best was proposed by two English botanist George Bentham (1800 - 1884) and Joseph Dalton Hooker (1817–1911). The classification was published in a three volume work as “Genera Plantarum” (1862–1883) describing 202 families and 7569 genera and 97, 205 species. In this system the seeded plants were classified into 3 major classes such as Dicotyledonae, Gymnospermae and Monocotyledonae.
Class I Dicotyledonae: Plants contain two cotyledons in their seed, leaves with reticulate venation, tap root system and tetramerous or pentamerous flowers come under this class. It includes three sub-classes – Polypetalae, Gamopetalae and Monochlamydeae.
Sub-class 1. Polypetalae: Plants with free petals and dichlamydeous flowers come under polypetalae. It is further divided into three series – Thalamiflorae, Disciflorae and Calyciflorae.
Carolus Linnaeus (1707 - 1778) was a great Swedish Botanist and said to be the “Father of Taxonomy.” He outlined an artificial system of classification in “Species Plantarum” in 1753, wherein he listed and described 7,300 species and arranged in 24 classes mostly on the basis of number, union (adhesion and cohesion), length, and distribution of stamens.
The classes were further subdivided on the basis of carpel characteristics into orders. Hence the system of classification is also known as sexual system of classification.
This system of classification though artificial, was continued for more than 100 years after the death of Linnaeus, due to its simplicity and easy way of identification of plants.
However the system could not hold good due to the following reasons.
1.Totally unrelated plants were kept in a single group, whereas closely related plants were placed in widely separated groups. Example:
a.Zingiberaceae of monocotyledons and Anacardiaceae of dicotyledonous were placed under the class Monandria since these possess single stamens.
b.Prunus was classified along with Cactus because of the same number of stamens.
No attempts were made to classify plants based on either natural or phylogenetic relationships which exist among plant groups.
2. Natural system
Botanists who came after Linnaeus realised that no single character is more important than the other characters. Accordingly an approach to a natural system of classification sprouted in France. The first scheme of classification based on overall similarities was presented by Antoine Laurent de Jessieu in 178
Bentham and Hooker system of classification
A widely followed natural system of classification considered the best was proposed by two English botanist George Bentham (1800 - 1884) and Joseph Dalton Hooker (1817–1911). The classification was published in a three volume work as “Genera Plantarum” (1862–1883) describing 202 families and 7569 genera and 97, 205 species. In this system the seeded plants were classified into 3 major classes such as Dicotyledonae, Gymnospermae and Monocotyledonae.
Class I Dicotyledonae: Plants contain two cotyledons in their seed, leaves with reticulate venation, tap root system and tetramerous or pentamerous flowers come under this class. It includes three sub-classes – Polypetalae, Gamopetalae and Monochlamydeae.
Sub-class 1. Polypetalae: Plants with free petals and dichlamydeous flowers come under polypetalae. It is further divided into three series – Thalamiflorae, Disciflorae and Calyciflorae.
Series (i) Thalamiflorae: Plants having flowers with dome or conical shaped thalamus and superior ovary are included in this series. It includes 6 orders and 34 families.
Series (ii) Disciflorae: Flowers having prominent disc shaped thalamus with superior ovary come under this series. It includes 4 orders and 23 families.
Series (iii) Calyciflorae: It includes plants having flowers with cup shaped thalamus and with inferior or sometimes with half inferior ovary. Calyciflorae includes 5 orders and 27 families.
Sub-class 2. Gamopetalae: Plants with united petals, which are either partially or completely fused to one another and dichlamydeous are placed under Gamopetalae. It is further divided into three series – Inferae, Heteromerae and Bicarpellatae.
Series (i) Inferae: The flowers are epigynous and with inferior ovary. Inferae includes 3 orders and 9 families.
Series (ii) Heteromerae: The flowers are hypogynous, superior ovary and with more than two carpels. Heteromerae includes 3 orders and 12 families.
Series (iii) Bicarpellatae: The flowers are hypogynous, superior ovary and with two carpels.Bicarpellatae includes 4 orders and 24 families.
Sub-class 3. Monochlamydeae: Plants with incomplete flowers either apetalous or with undifferenciated calyx and corolla are placed under Monochlamydeae. The sepals and petals are not distinguished and they are called perianth. Sometimes both the whorls are absent. Monochlamydeae includes 8 series and 36 families.
Class II Gymnospermae: Plants that contain naked seeds come under this class. Gymnospermae includes three families – Gnetaceae, Coniferae and Cycadaceae.
Class III Monocotyledonae: Plants contain only one cotyledon in their seed, leaves with parallel venation, fibrous root system and trimerous flowers come under this class. The Monocotyledonae has 7 series and 34 families.