Gap in convergent evolution?

In a thread about lawn grasses, @psweet commented,

One problematic aspect to this is that turf grasses in general aren’t native to North America

I find that unexpected. We know about convergent evolution – unrelated lineages on different continents resembling each other because of similar habitats and survival strategies. Thus we have gazelles and similar antelopes in African grasslands, and pronghorns in North American grasslands. These are not closely related, but they occupy similar ecological niches and thus resemble each other.

So, comparing North American steppes with Eurasian steppes – they are at similar latitudes, have similarly continental climates, and prehistorically (and to some extent historically) were subject to grazing by large hoofed mammals. Why, then, would North American grasses not have evolved into turf-building forms like Eurasian grasses did?

If it’s true, my thoughts go towards the soil/microbiota itself. Earthworm distribution, but also maybe different mycorhizal associations as well. Also, I think there’s a different fire ecology in North America.

Just because something can happen doesn’t mean that it will, or even that it’s the best approach.

Assuming that the premise is correct, grasses in the Americas found a different and equally effective strategy, that’s really about as far as it goes.

The principle of convergent evolution doesn’t state that the the outcome has to be identical in every case. Cetaceans that went back to the sea converged with predatory sharks and ichthyosaurs, but their tail orientation is different. Birds, bats, and pterosaurs all evolved wings supported by front limbs, but they all did so in different ways. It’s convergent, but it is not identical.

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i think your quoted statement should be interpreted as “the most commonly used grasses for lawn applications aren’t native”, not that:

for example, Bouteloua dactyloides (Buffalo Grass) is native to parts of North America, and it can be used as turf grass. it’s relatively water efficient (although it tends to turn brown in drought), but it’s very slow growing and doesn’t handle traffic very well. so it’s not the first choice for most people for turf grass.

there are other native grasses and sedges that could be used for lawn applications, too, but they also have features that aren’t as desirable for lawns (ex. tall flower spikes that “look messy”, etc.)

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Convergent evolution is used to describe a phenomenon of creatures evolving traits independently. As they say birds have wings and bats have wings too. These two groups of creatures are not very related. I guess they are still related in some ways. As for grasses, these plants are grouped under Poaceae. These species will be more related and most species look just like grass. I do not know North American grass and Eurasian species, but I’ll make a guess that the land is linked at some point in time or the seeds can be spread by birds and wind. I know St Augustine grass. This is from central America and African coastline. It is for warmer climate.
I guess after rain, the Eurasian steppe will look like meadows. but I’ve not been there. Rain is not abundant at some places on earth, so the grasses are not always green and lush.

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I understand that turf is an anthropological design not necessarily a natural phenomena and the Eurasian grass strains used for the development of lawn turf have been developed over time by human interference, perhaps the different American grass species/strains have not been put through the same process.

Those grasses lived like that without humans.

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Yes, tuff grass need to be mowed regularly to make it look dense. There are cultivated varieties. These cultivars need maintenance too.
One example of tuff grass… Zoysia japonica. The wild species is probably a dense small grass to begin with. It is commonly used for golf course. There may be an industry utilising it, so there is research on it to select suitable cultivars.

there definitely are turfgrass cultivars developed from American natives. just for example, Paspalum vaginatum has been bred into SeaIsle 1, SeaIsle 2000, SeaStar, Aloha, etc…

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Perhaps the “in general” part of his comment was overlooked. Or perhaps there are just as many turf-building grasses in NA and Eurasia after all? Native North American turf-building grasses include buffalograss, fescue, bentgrass, blue grama, sideoats grama, curly mesquite grass, seashore paspalum, and even St. Augustine is thought to be native to coastal Florida.

So perhaps there’s just as many turf-building grasses in NA as any other place. And maybe steppe environments aren’t the center of turf-forming grass evolution? I think bunch-grasses are the dominant grasses in the Eurasian steppe as they are in NA–and most of our exotic turf-grasses don’t hail from the Eurasian steppes.

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Just yesterday I planted a patch of turf with Bouteloua gracilis, which is native to North America, and so are many other species that can be grown as turf (e.g. Festuca rubra, Agrostis pallens, etc.). After thinking about this further, though, I realized that most of the cultivated grasses native to North America are bunch/tussock grasses, which leads me to agree with @pfau_tarleton that “maybe steppe environments aren’t the center of turf-forming grass evolution.” On steppes, and especially in tall-grass prairie, the grasses are… tall, unsurprisingly. Because they need to compete with so many other plants for light, they’ve evolved to grow much taller than is desirable in a turf grass. In contrast, I’ve seen many grasses growing on sand dunes that would be perfectly suitable for turf because they tend to be low-growing and mat-forming, presumably due to the lack of competition for light and the necessity to essentially float above the sand by creating a raft. Perhaps it’s environments like sand dunes, not steppeland prairie, where most of the spreading, sod-forming grasses like Cynodon dactylon and Cenchrus clandestinus originated.

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  1. As noted above, the fact that an ecological niche is available doesn’t mean that anything will evolve to fill it. Though “turf grass” or “spreading grass-like plant” is such an obvious niche you’d think things would evolve to fill it.

  2. Rhizomatous, spreading, turf-forming grasses and sedges do exist in North America. Examples include Buffalograss, Switchgrass, forms of Red Fescue, some bentgrasses, field sedge, etc., etc.

  3. Conditions aren’t the same in North America as in parts of Europe and Asia where cattle and horses were domesticated millennia ago. Farmers and herders keep domesticated grazers on the same ground for longer than they could remain under more natural conditions, creating tremendous selection pressure for low-growing, spreading grasses that can survive near-continuous grazing.

  4. Euroamericans came here with preferred, often cultivated grasses. Their incentive to cultivate the wild species was not high. For example, our native bentgrasses Agrostis pallens and A. hallii are morphologically similar to European species introduced for forage and lawns, but why develop them when the introduced species are highly aggressive and work well?

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