BOTANY,Semester 02,MBOTCC 06,Contemporary system of classification:Armen Takhtajan,D.K.Jha (lecture series no. 06).
ARMEN TAKHTAJAN (B.1910) was Head of the Dept. Of Plant Science at Leningrad,Russia.He presented a system of classification of Angiosperms for the first in 1942 and thereafter it’s revised versions in 1954,1966,1969 and finally in 1980 in his book in English entitled Flowering Plants ;Origin and Dispersal.His system is basically inspired by Bassey_Hallier tradition as he also considered evidences from fields like Morphology,Anatomy, Embryology, Cytology,Palynology ,Chemistry etc. According to Takhtajan angiosperms aremonophyletic in origin and have derived from Gymnosperms.Monocots are derived from some primitive dicots.
Takhtajans classification is based on some phyletic principles:
1Woody plants are primitive than herbaceous plants.
2.Deciduous woody plants are derived from evergreen plants.
3.Stomata without subsidiary cells are more advanced than stomata with subsidiary cells.
4 .Alternate lead phyllotaxy is more primitive than other types.
5.Parallel venation is advanced.
6.Cymose inflorescence is primitive than racehorse.
7.Polymerous flowers are primitive.
8 Pollen with smooth exine is primitive than sculptured exine.
9. Apocarpous gynoecium is more primitive than syncarpous.
10.Bitegmic ovules are more primitive than unitegmic.
11.Anatropous ovules are more primitive than others.
12.Polygonum type embryosac is most primitive.
13.Porogamic condition is more primitive than mesogamic and chalazogamic.
14. Many seeded follicle fruits are most primitive.
15. Endospermic seeds are primitive.Dicot embryo is primitive than monocot embryo.
Brief outline of Takhtajans system
Takhtajan has replaced traditional nomenclature of Angiosperm,Dicotyledonae and Monocotyledonae by Magnoliophyta,Magnoliopsida and Liliopsida respectively.
All the Angiosperms have been included into Division Magnoliophyta which has further been divided into 02 classes:Magnoliopsida (Dicot) and Liliopsida (Monocots).Magnoliopsida has been further divided into 11 subclasses and Liliopsida has been further divided into 06 subclasses.All the subclasses of Magnoliopsida and Liliopsida have been further divided into 50 and 16 super orders respectively.The supersedes have been divided into orders.
Division:Magnoliophyta
Class 01:Magnoliopsida
Subclass:
1.Magnolidae
2.Nymphaeidae
3.Nelumbonidae
4.Ranunculidae.
5.Cariophylliadae
6.Hamamelidae
7.Dilleniidae.
8.Rosidae.
9.Carnidae
10.Asteridae
11.Lamiidae.
Class02:Liliopsid
Subclass:
1.Lilidae
2.Commelinidae
3.Arecidae
4.Alismatidae
5.Triurridae
6.Aridae.
According to Takhtajan the order Magnoliales is the most primitive among the flowering plants.All other Angiosperms have been derved from Magnoliales.
The order Alismatales have been supposed to be most primitive among Monocotyledons
The highest evolved order among dicot is Asterales,and Arales among Monocots.
Winteraceae was considered to be the most primitive family. Merits of the System
1.Magnoliopsida is considered primitive to Liliopsida.
2.Families are small in size.
3 Dicots start with most primitive Magnoliales.
4.Monocots start with most primitive Alismatales.
Demerits of the system
1.Derivation of Monocots from the stock ancestral to theNymphaeales.
2.Taxa are extremely narrowly defined.
3.Unwanted splitting of related groups.
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