C4 plants

Plants that produce a four-carbon compound during photosynthesis, mainly of tropical origin, including grasses and the agriculturally important crops maize, sugar cane, millet and sorghum.

The C4 photosynthesis mechanism is more efficient than the older C3  mechanism. It is believed that C4 evolved sometime during the last 50 million years as an evolutionary adaptation to falling CO2 levels in the atmosphere.

Definition based on (revised from) IPCC AR4.