Armen Takhtajan (1910-2009) was one of the most influential botanists and systematists of 20th century. He worked as a paleobotanist in Komarov Botanical Institue of Leningrad, USSR (present day Russia). While working in the institute, Takhtajan in 1942 developed a classification scheme for flowering plants which emphasized phylogenetic relationships between plants.
This first attempt made the arrangement of classification upto the orders of higher plants, based on the structural types of gynoecium and placentation.
After 12 years i.e. in 1954, the actual system of classification was published in ‘The Origin of Angiospermous Plants’ in Russian language. It was translated in English in 1958. Later on in 1964, he proposed a new system of classification in Russian language. To trance the evolution of angiosperm, he was particularly inspired by Hallier’s attempt to develop a synthetic evolutionary classification of flowering plants based on Darwinian philosophy.
The classification was published in ‘Flowering Plants: Origin and Dispersal’ (1969) in English. Later on, in 1980, a new revision of his system was published in ‘Botanical Review’.
Outline of Classification
In the class Magnoliopsida,
- Most primitive order: Magnoliales
- Most advanced order: Asterales.
In the class Liliopsida,
- Most primitive order: Alismatales
- Most advanced order: Arales.
Principles of Classification
|Growth habit||Woody habit||Herbaceous habit|
|Small woddy angisoperm||Large trees of tropical rain forests|
|Sparingly branched trees||Trees with numerous slender branches|
|Evergreen plants||Deciduous woody plants|
|Leaves||Simple leaves||Compound leaves|
|Reticulate venation||Parallel venation|
|Alternate leaves||Opposite leaves|
|Stomata||Mesogenous type||Peigenous type|
|With subsidiary cells||Lacking subsidiary cells|
|Nodal structure||Tri to pentalacunar type||Unilacunar type|
|Floral structure||Indefinite and variable number of floral parts arranged spirally on an elongated axis.||Fixed number of floral parts arranged in cyclic pattern on a short axis|
|Pollen grains||Exine devoid of external sculpturing||Sculpturing is of various types|
|Monocolpate (dicots)||Ticolpate (dicots)|
|Ovules||Anatropous ovule||Other types|
|Crassinucellate ovules||Tenuinucellate ovules|
|Gametophyte & fertilization||monosporic Polygonum type||Tetrasporic type|
|Seeds||Abundant endosperm with a minute and undifferentiated embryo||Endosperm is reduced or wanting and the embryo is large and well differentiated|
|Fruits||Many seeded follicular fruit develop from multicarpellary apocarpous gynoecia.||Coenocarpous fruits|
Merits of Takhtajan’s classification
- The classification of Takhtajan is more phylogenetic than that of earlier systems.
- This classification is in a general agreement with the major contemporary systems of Cronquist, Dahlgren, Thorne, and others.
- Nomenclature adopted in this system is in accordance with the ICBN, even at the level of division.
- The treatment of Magnolidae as a primitive group and the placement of Dicotyledons before Monocotyledons are in agreement with the other contemporary systems.
- In this system, more weightage is given to cladistic information in comparison to phenetic information.
- This system provides classification only upto the family level, thus it is not suitable for identification and adoption in herbaria.
- Takhtajan recognised angiosperms as division which actually deserve a class rank like that of the systems of Dahlgren (1983) and Thorne (2003).
- Numerous monotypic families have been created in 1997 due to the further splitting and increase in number of families to 592 (533 in 1987), resulting into a very narrow circumscription.
- Takhtajan incorrectly suggested that smaller families are more ‘natural’.
- Although the families Winteraceae and Cancellaceae showed 99 to 100% relationship by multigene analyses, Takhtajan placed these two families in two separate orders.
- Lecture of Professor Dr. Oliur Rahman, University of Dhaka. (Some of the points are paraphrased here. And many data were taken from internet. If this article has any error, only the author is to blame.)