The question doesn't apply to the first example (Liatris) because those are two species, neither is a cultivar. Cultivars are recognized by the name in quotes - 'Little Joe', as in your second example.

I don't know of any scientific proof that a cultivar doesn't have the same benefit although some people believe that is so.

I suspect if there is any difference it has to do with if the species itself (in the case of this cultivar it is apparently Eupatorium dubium) is native to your area in general. Again, using this example, this species is native to coastal areas so I'd say that using it in Ohio is not as close a match as using E. fistulosum or a cultivar of that (which I am not sure there is any cultivar of E. fistulosum).

Hope that helps.

My opinion only here...but in my experience the "named" plants - especially ones with unusual colors or variegation, are not as robust as their unnamed, unrefined sisters. Many of the cultivars are bred/propagated for a specific desired trait - color, size, sterile, etc. and that is why people choose them. If those traits are not important, named (and often more expensive) plants are not needed so opt for the non-cultivar plants.

FataMorgana

I think it varies a lot, but if a straight species plant will work for you, that's probably better. Some cultivars are cloned which makes for less diversity in the gene pool, some I think are slightly different naturally occurring plants.

I have many cultivars which I see wildlife use all the time (but then again I see them using exotics including invasives too).

If I can only get the cultivar or the cultivar has some advantage like a different color flower or height I want I'll buy it. I bought a cultivar of goldenrod (Soldago) which drives me crazy because it spreads so much more than the straight species one does. Otherwise I've mostly been happy with cultivars I have, although I feel better about using the straight species and will unless there's a reason not to.

I think as long as it is a native genus, there should be no worry. In fact, the cultivars of Joe Pye weed can be really spectacular since the native is pretty bland to me. However, living in the prairie, I never experiment with grasses.

Depends entirely on what your goals are: If you are trying to recreate a plant community that may have existed in your area prior to settlement, matching actual local genetics is important, though often very difficult. If you are trying to create a plant community with as much genetic diversity as possible, than cultivars should be avoided, as they, by definition, are all of one genotype.........or close to it in the case of "seed varieties". In terms of aesthetics, it is entirely your call.

Finally, keep in mind, some folks get passionate about decrying the use of any cultivar at any time within a naturalistic planting. But you mention "Little Joe" variety of Joe Pye weed. Who's to say, that cultivar does not more closely match what your area originally had growing there, as opposed to the taller plants typical of seed strains.

It gets complicated.................+oM

Lots of great responses...I'd like to add that breeding plants for specific traits such as height, specific colors, double petals, and such *could* result in less nectar being produced or in accessible nectar due to elongated tubes, making them inaccessible to short tongue bees and such. Unintended results of developing cultivars is, perhaps, another reason one would endorse using straight species.

hi, I don't get around to this forum much but just wanted to chime in.

Somewhere in the back of my head I remember a zinnia study in which they measured which strains were most attractive to butterflies... I'm going to assume they were also the ones with the most nectar or most accessible nectar. I think it was clearly the older strains that were most visited.... I think thumbelina was on top.... so yes improved varieties don't always provide the same benefits as the straight species.

I like the idea of planting natives and I'm sure they are a better fit for an ecosystem but my thought is that any highly selected cultivar might almost "pollute" the gene pool with some odd genetic trait that might be pretty, but might edge out some more efficient trait.

Just off the top of my head maybe a large planting of dwarf new england asters in a garden might cross with the normal wild population and produce a large percentage of dwarf seedlings that cannot compete in a wild setting.

Kato_b,

That is a great example for being just off the top of your head. "...maybe a large planting of dwarf new england asters in a garden might cross with the normal wild population and produce a large percentage of dwarf seedlings that cannot compete in a wild setting."
I was not familiar with the zinnia study...but that does support the idea I was trying to express.

...and for anyone who happens upon this thread in search of natives to plant, just an FYI, the zinnias are native to Mexico, but their native range doesn't include the U.S. (at least not to my knowledge).