Survey of cool and warm season grasses

Most prairie and savanna restorationists are aware that there are two classes of grasses, distinguished by a fundamental property of photosynthesis (abbreviated C3 and C4). Many prairie grasses have the C4 pathway, and because of this are able to proliferate in warmer parts of the summer when other plants are suffering from moisture stress. For the most part, prairie grasses are warm season grasses, and savanna grasses are cool season grasses. The C3/C4 differentiation is a good example of evolution in action, and botanists have been able to explain at a fairly fundamental level how these two kinds of grasses differ.

I recently spent some time putting together a table that sorts out these two kinds of grasses, based on an extensive review that was published by S.S. Waller and J.K. Lewis in the Journal of Range Management (1979; vol. 32, pp. 12-28). Note that my table is just a subset of that of Waller and Lewis since they have a lot of grasses that we are not familiar with here in the Midwest.

As I indicated, the C3/C4 phenomenon is an interesting evolutionary development that relates to the ability of plants to tolerate drought. The explanation is fairly sophisticated, but the Wikipedia pages on this are very good. See this link. (What would be do without Wikipedia?)

Essentially, the C4 pathway permits plants to carry out photosynthesis during warm (or hot) summer conditions, making them able to outcompete C3 plants.

Note that in our temperate climate, the only C4 plants are grasses, but in the tropics many broadleaf plants have the C4 pathway.

It is interesting that although C4 plants represent only 5% of the Earth's plant biomass, and only 1% of the known plant species, they account for about 30% of terrestrial carbon fixation.

C3 and C4 grasses: abbreviated from Waller and Lewis

Genus	Common name	C3	C4
Agropyron	Wheat grass (not agricultural wheat, which is Triticum)	*
Agrostis	Bent grass	*
Andropogon	Big bluestem		*
Avena	Agricultural Oats	*
Bouteloua	Side oats		*
Bromus	Brome	*
Calamagrostis	Blue-joint	*
Dactylis	Orchard grass	*
Deschampsia	Hair grass	*
Dichanthelium (formerly Panicum) latifolium; leibergii; oligosanthes; praecocius	Panic grass	*
Digitaria	Crab grass		*
Echinochloa	Barnyard grass		*
Elymus	Wild rye	*
Eragrostis	Love grass		*
Festuca	Fescue	*
Glyceria	Manna grass	*
Hordeum	Barley	*
Koeleria	June grass	*
Leersia	Rice cut grass	*
Lolium	Perennial rye grass	*
Muhlenbergia	Muhly grass		*
Oryza	Rice	*
Panicum virgatum Panicum capillare Some other species of Panicum are C3 grasses	Switch grass Witch grass		*
Paspalum	Paspalum grass		*
Phalaris	Reed canary grass	*
Phleum	Timothy	*
Poa	Blue grass	*
Pragmites	Common reed grass	*
Schizachyrium	Little bluestem		*
Secale	Cereal rye	*
Setaria	Foxtail		*
Sorghastrum	Indian grass		*
Sorghum	Broom-corn		*
Spartina	Cord grass		*
Sphenopholis	Wedge grass	*
Sporobolus	Dropseed		*
Stipa	Needle grass	*
Triticum	Wheat	*
Zea	Corn		*

According to the Wikipedia article: "C₄ carbon fixation has evolved on up to 40 independent occasions in different families of plants, making it a prime example of convergent evolution. C₄ plants arose 25-32 million years ago (Oligocene)... and did not become ecologically significant until around 6-7 million years ago (Miocene). C₄ metabolism originated when grasses migrated from the shady forest undercanopy to more open environments, where the high sunlight gave it an advantage over the C₃ pathway."