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We studied activity of photosynthetic enzymes (RuBP carboxylase, PEP carboxylase, ATT, and NADP-ME) in 51 species of plants from the arid zone of Central Asia with the C4 and C3 types of CO2 fixation. Plants with the C4 syndrome (12 species of grasses and 23 species of the goosefoot family) differed from C3 species in lower activity of RuBP carboxylase and a high level of PEP carboxylase. In the group of C4 grasses, those of the tribes Andropogoneae, Aistideae, and Paniceae are shown to belong to the NADP-ME biochemical type, while species of the tribe Cyonodonteae belong to the NAD-ME biochemical type. High activity of AAT is demonstrated in species of the goosefoot family with the coronary syndrome, even in malate species. A relationship between types of Kranz anatomy and biochemical groups is clarified within the family Chenopodiaceae, and the NAD-ME mechanism of CO2 fixation is shown to have arisen first in evolution of the C4 syndrome of the goosefoot family. A classification of C4 species of the goosefoot family is proposed that takes into account activity of photosynthetic enzymes, the type of Kranz anatomy, the life form, and ecological conditions of the habitat of species. It reflects the process of adaptation and ecological differentiation of plants under different soil-climatic conditions of the arid zone. In C3 species of the desert flora, species diversity is demonstrated for the activity of enzymes (including enzymes of the dicarboxylic acid cycle), and this was of great significance to formation of the C4 syndrome.