Occurrence of C 3 and C 4 Photosynthetic Pathways in North American Grasses

A literature survey was made for the occurrence of C3 and C4 photosynthetic pathways in the United States Gramineae. Distinctive characteristics of the two photosynthetic pathways are discussed. Leaf anatomy, CO2 compensation point, net enhancement of photosynthesis in oxygen-deficient atmosphere, 13 C discrimination, and initial product labeling were criteria selected to evaluate data for 6 subfamilies including 25 tribes, 138 genera, and 632 species. The Arundinoideae, Bambusoideae, Oryzoideae, and Pooideae (Festucoideae) are composed of species with C3 pathways. All tribes within the Eragrostoideae have C4 pathways with the exception of Unioleae. Within the Panicoideae, the Andropogoneae and all of the Paniceae, excepting the genera Sacciolepus, Isachne, Oplismenus, Amphicarpum, and Panicum, have C4 pathways. The subgenus Dichanthelium within Panicum is C3 while the Eupanicum subgenus contains plants with both C3 and C4 photosynthetic pathways.