The C4 photosynthetic carbon cycle can be explained as the elaborated addition to the C3 photosynthetic pathway. It is a unique series of biochemical, anatomical and regulatory gene characteristics that concentrate CO2around the carboxylating enzyme Rubisco, thereby increasing photosynthetic efficiency during high rates of photorespiration. The C4 photosynthetic pathway has evolved as an adaptation to high light intensities, high temperatures and dryness, therefore in the warmer climates of the tropical and subtropical dominating the grassland floras and biomass production. C4 photosynthesis originated more than 40 times independently during angiosperm evolution in over 15 families of angiosperms, representing convergent evolutionary phenomena. Probably, C4 grasses evolved in the early Oligocene about 30 million years ago, while later appeared C4 dicots, less than 20 million years ago. Low atmospheric CO2 is pivotal factor forC3- C4 transition, because it is required for high rates of photorespiration. Consistently, the increasing global aridification and declining atmospheric CO2 coincides with periods of the appearance of C4plants. Genetically, leading mechanism for creation of C4 genome is duplications of whole genomes, genome segments, or single genes followed by non-functionalization and neo-functionalization with selection for carbon conservation traits under high photorespiration promoting conditions being the ultimate factor behind the origin of C4 photosynthesis.
