Armen Takhtajan (born 1910) is a Russian botanist, one of the most important figures in 20th Century plant evolution and systematics and biogeography. His other interests include morphology of flowering plants, paleobotany, and the flora of the Caucasus.

Takhtajan worked at the Komarov Botanical Institute in Leningrad, where he developed his 1940 classification scheme for flowering plants, which emphasized genetic relationships between plants and plant evolution. His system did not become known to botanists in the West until after 1950, and in the late 1950's he began a correspondence and collaboration with the prominent American botanist Arthur Cronquist , whose plant classification scheme was heavily influenced by his collaboration with Takhtajan and other botanists at Komarov.

The 'Takhtajan System' of flowering plant classification treats flowering plants as a division (phylum), Magnoliophyta, with two classes, Magnoliopsida (dicots) and Liliopsida (monocots). These two classes are subdivided into subclasses, and then superorders, orders, and families. The Takhtajan system is similar to the Cronquist system, but with somewhat greater complexity at the higher levels. He favors smaller orders and families, to allow character and evolutionary relationships to be more easily grasped. The Takhtajan classification system remains influential; it is used, for example, by the Montréal Botanical Garden.

Takhtajan also developed a system of floristic regions.

Takhtajan is a member of the Russian Academy of Sciences, as well as as foreign associate of the U.S. National Academy of Sciences since 1971. The standard botanical author abbreviation Takht. is applied to species he described.

Selected works

• Floristic Regions of the World (1986) by Armen Takhtajan, Theodore J. Crovello and Arthur Cronquist .
• Evolutionary Trends in Flowering Plants (1991) by Armen Takhtajan and A. L. Takhtadzhian .
• Diversity and Classification of Flowering Plants (1997) by Armen Takhtajan and A. L. Takhtadzhian .