- Grasses are often divided into warm-season grasses and cool-season grasses. The warm-season grasses are C4 plants that grow best during the summer months, when the C4 process is much more efficient. They are also more tolerant of drought. The cool-season grasses, by contrast, thrive in spring and fall. Many of the prairie grasses of America's Great Plains are C4 warm-season grasses. Switchgrass, Indiangrass, big and little bluestem are all examples.
- The grass family is called Poaceae, and it's divided into a number of different subfamilies. Some of these consist solely of C4 grasses, others of C3 grasses, and still others of both C3 and C4 grasses. The Pooideae, Danthonioideae, Bambusoideae, Centothecoideae and Ehrhartoideae subfamilies are C3. The Panicoideae and Micrairioideae subfamilies include both C3 and C4 members, while the Aristidoideae and Chloridoideae are C4.
- As noted in a 2009 study in "Proceedings of the National Academy of Sciences," the C4 photosynthetic pathway is a relatively recent evolutionary innovation, although the driving forces leading to its emergence are still not entirely clear. It's thought the C4 pathway has evolved multiple times, which is an example of what biologists call convergent evolution -- a situation where two lineages independently evolve similar traits.
- C4 grasses are higher-efficiency, but they do not prosper equally in all environments. They generally have higher light requirements and higher temperature requirements than their C3 brethren. C3 grasses often have better frost tolerance. Despite these drawbacks, C4 grasses are more productive than C3, which is one of the reasons C4 grasses such as corn and pearl millet have become hugely successful as human crops.
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