Billions of years of evolution have not directly solved the problem of O2 fixation by Rubisco or CO2 loss by photorespiration. Evolution has never produced an oxygenase-free Rubisco or a photorespiratory pathway that does not involve CO2 loss. However, in just the last 35 million years, C4 photosynthesis has evolved independently from C3 ancestors over 60 times in flowering plants.^1,2 C4 photosynthesis solves the problems of O2 fixations and photorespiration by compartmentalizing Rubisco, most typically in the vascular sheath cells that surround the leaf veins, and biochemically concentrating CO2 within this compartment. CO2 is first fixed by the enzyme PEP carboxylase in the surrounding mesophyll cells, and the resulting four-carbon acids from which the name C4 is derived diffuse into the sheath cells. CO2 is then released by one of three decarboxylating enzymes, elevating the CO2 concentration at the site of Rubisco up to tenfold higher than C3 plants and essentially eliminating photorespiration.⁹ The compartmentalization of Rubisco and the Calvin cycle creates a dark green, wreath like appearance of the veins in cross-section due to the high number of chloroplasts in the sheath cells. This is known as Kranz anatomy, after the German word for “wreath.” Most of the known C4 species have been identified by this unique anatomy.