Takhtajan Classification System

Introduction

Armen Leonovich Takhtajan (1910 – 2009) was a Soviet- American botanist. He was one of the most important figures of the 20^th century for his work on plant systematics, evolution, and biogeography.

He was interested in the morphology of flowering plants, paleobotany, and the flora of the Caucasus. He developed his classification scheme for flowering plants. This classification emphasized phylogenetic relationships between plants.

His system was not known to botanists in the west until the 1950s. The classification system of Cronquist was greatly influenced by Takhtajan. He developed the classification system of higher plants.

Features of Classification System of Takhtajan

His system is based on phylogenetic system of classification. This system has greatly influenced all recent systems of classification.

His system of classification is inspired by Hans Hellier’s earlier theories.

The preliminary diagram of the phylogeny of orders of Angiosperms was published by him.

He subdivided both monocots and dicots into subclasses. This was his great achievement. This is widely accepted as a major advancement in angiosperm classification.

This system is synthetic and integrated which is based on all available data. This data includes the studies of cytology, genetics, comparative anatomy, photochemistry, embryology, and molecular data.

He studied the floristic composition of different regions. His book contains the floristic division of the whole world. It also contains lists of endemic families and genera. Endemic species of each region are also mentioned.

He mentioned various examples of parallelism and convergent evolution from Angiospermic families. He used available contemporary records and molecular data to organize these species into their respective families.

The hypothesis of Takhtajan was tested by DNA analysis by Peter Steven and found perfect.

Although there is a similarity in Cronquist and Takhtajan classification systems. But the system of the former has complexities at higher levels whereas Takhtajan favors smaller orders and families.

His system allows evolutionary relationships to be more easily grasped.

System of Classification

In his system of classification, flowering plants are divided into two classes:

Class Magnoliopsida

Also known as dicotyledons includes 8 subclasses, 126 orders, 440 families, almost 10500 genera, and no less than 195,000 species. This class is divided into the following subclasses.

Class Magnoliopsida

1. Subclass Asteridae
2. Subclass Caryophyllidae

• Subclass Dilleniidae

1. Subclass Hamamelididae
2. Subclass Magnoliidae
3. Subclass Rosidae

Class Liliopsida

Also known as monocotyledons and includes 4 subclasses, 31 orders, 120 families, more than 3000 genera, and about 65000 species. This class is divided into the following subclasses.

1. Subclass Alismatidae
2. Subclass Arecidae

• Subclass Commelinidae

1. Subclass Liliidae
2. Subclass Zingiberidae

Merits of Takhtajan classification system

1. It is based on phylogenetic relationships. Most of the groups are formed on the basis of principles of the phylogeny.
2. Families are small homogenous units composed of closely related genera.
3. This system is better organized on the basis of evolutionary relations than old systems.
4. Angiosperms are monophyletic according to this system and are originated from dicots.
5. Angiosperms are treated as one division.

Demerits of Takhtajan classification system

1. Although, this system is phylogenetic but still not helpful for classification up to the family level.
2. Narrow criteria are used for defining taxa in the system. It causes unwanted splitting of relative genera.
3. The main drawback of this system is that it says, monocot is derived from main ancestor to Nymphaeales.
4. In this system, monocots are placed after dicots. But modern and recent systems place monocots between primitive angiosperms and Eudicots.