Direction of evolutionary variability of parameters of genome size and structurally functional activity of plants on life forms groups and angiosperms taxa are analyzed. It is shown that, in the Cretaceous-Cenozoic, their nuclear genome tended to increase. Functional genome efficiency (intensity of functions per 1 pg of DNA) decreased from as much as possible high at trees and lianas of rain and monsoonal forests of the Paleogene to minimum at shrubs, perennial and annual grasses of meadow-steppe vegetation which had appeared in the neogene. Important for the vegetation environmental changes in temperature, humidity and CO2 concentration in an adverse direction are discussed as the cause of evolutionary genome size growth and decrease in its functional efficiency. Price for phylogenetic adaptogenesis of angiosperms to the step Cenozoic climate cooling was 4-fold and more genome growth.