The identification of plant functional groups allows to evaluate plant properties as: recovering capacity, regeneration and resistence to environmental changes. It is possible to define plant functional groups in the seasonal savana and the high barren plateau taking in to account the ecophysiological plant responses to water stress and daily temperature-water rythmn, respectively. In the savana, although the wooden component is constituted by evergreen and deciduous tree species, they make only a functional group taking in to account their responses to water stress, this is similar in the herbaceous component. Results suggest that a change in environmental factors may generate a floristic replace without major changes in the system function.However, in the high barren plateau, the different life forms also constitute different functional groups according to plant responses to temperature-water factor, suggesting that the substitution of any group will put in danger the preservation of this ecosystem.