Merits and Demerits of Takhtajan’s Classification

Takhtajan's classification

Armen Takhtajan significantly contributed to the field of taxonomy by proposing a phylogenetic classification system. He was a Russian taxonomist who worked at the Komarov Botanical Institute in Leningrad which is now called St. Petersburg. He published his classification in 1954 in the Russian language which was translated into English as “The Origin of Angiospermous Plants” in the year 1958. In this article, we will be discussing the merits and demerits of Takhtajan’s classification.

Takhtajan’s Classification

Before digging into the merits and demerits of Takhtajan’s classification, let’s take a look at the features of the classification system. He considered important evidence from various fields of botany namely anatomy, embryology, palynology, vegetative and floral morphology), as well as geographical distribution etc. for the delimitation and circumscription of orders and families. He considered angiosperms to be monophyletic in origin. Takhtajan divided the Angiosperms into two classes Magnoliopsida (Dicotyledons) and Liliopsida (Monocotyledons). Magnoliopsida is further sub-divided into 7 subclasses, 20 superorders, 71 orders and 342 families. Liliopsida is further sub-divided into 3 subclasses, 8 superorders, 21 orders and 77 families.

Takhtajan considered the following in deciding the relative degree of advancement in flowering plants-

1. Woody plants are more primitive than herbaceous ones. 
2. Simple leaves having an entire margin with pinnate venation are more primitive than palmately lobed and compound leaves.
3. Pinnate venation is primitive to palmate venation. Parallel venation is most
advanced.
4. Alternate leaf arrangement is primitive as compared to opposite and whorled
arrangement.
5. Stomata with subsidiary cells are more primitive than the ones without subsidiary cells.

6. The solitary and terminal flowers are primitive. The cymose inflorescence is more
primitive than racemose.
7. Flowers with the moderately elongated floral axis with an indefinite and variable numberof floral parts are primitive.

8. Monocolpate pollen grains are primitive and evolved into tricolpate pollen
grains.
10. Pollen exines without external sculptures are primitive where as those with various
types of sculptures are advanced.
11. Primitive carpels are free having many ovules and laminar placentation.
12. Anatropous ovule is a primitive type from which all other different ovules are derived.
13. Primitive type of female gametophyte is monosporic eight nucleate (Polygonum type) from which different types are derived. The Tetrasporic type of female gametophyte is the most advanced.
14. Primitive seed is of medium size from which small and large seeds are derived. Primitive seeds had abundant endosperm with minute and undifferentiated embryos.
15. Many seeded follicles from multicarpellate, apocarpous gynoecium is primitive basic type.

Takhtajan's classification

Merits and Demerits of Takhtajan’s Classification

The merits and demerits of Takhtajan’s Classification are discussed below.

The merits of this classification system are:

1. The classification is based on well-established phylogenetic principles.
2. The nomenclature of various groups is in according to the rules of the ICBN.
3. The earlier grouping of the angiosperms has been replaced with definite “subclasses”. Thus, the division of the dicotyledons (Magnoliopsida) and monocotyledons (Liliopsida) into defined “subclasses” has been considered a significant advancement.
4. The system follows a natural assemblage of families, based on analysis of information obtained from various branches. Thus, the families Lamiaceae and Verbenaceae are positioned together in the order Lamiales; Caryophyllaceae, Chenopodiaceae and Portulacaceae are put together in the order Caryophyllales.
5. Dicots begin with Magnoliales as the most primitive angiosperm is universally accepted.
6. The position of Magnoliales at the start of Magnoliopsida is in accordance with evolution.
7. The concept of primitive flower in the classification is in accordance with modern-day taxonomists.
8. Bubble diagram suggested by Takhtajan showing relationships between different groups subclasses and
superorders are helpful in taxonomic studies.

The de-merits of this classification system are:

1. The taxa are too narrowly defined which has resulted in the undesirable splitting of related taxa.
2. The classification is only till the family level and key for identification are also not given. Hence, it is less useful.
3. Few of the phyletic principles given by Takhtajan are not accepted by present-day taxonomists.
4. Takhatajan considers Degeneriaceae as the most primitive angiosperm but many today’s taxonomists consider Winteraceae to be the most primitive family in angiosperms.
5. The classification incorporates data from a number of branches but greater emphasis is given to cladistic information as compared to phenetic information ie. morphological features.

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Also read: Merits and Demerits of Bentham and Hooker classification – My Biology Dictionary

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