A cultivar is not likely to become any more invasive than the native plant; they are, after all the same species and any genes available for sharing with the native plants will have already been in existence.

From an ecological point of view, it depends what kind of cultivar is being planted. If the plants are vegetatively propagated then one has the debate about genetic diversity and maintaining a diversed gene pool. If selections of tetraploids, then the plants may be sterile and not a food source for seed eaters or the flowers may lack nectar for insects.

In a large restoration project for a wild area, one would want to use unnamed, open pollinated seed to maximize the gene pool for sustainability. In a home garden, one is not relying on self seeded plants so diversity is not as important.

As a native plant gardener,the "unimproved" versions of plants often have smaller flowers and are less predictable than the cultivars. This endears them to me, but traditional gardeners may prefer "better" plants. So I would rather see someone using a native cultivar than using a non native.

But judy, I am more specifically wondering whether the native cultivars might not compete with and push out populations of their native species equivalents. That is, I'm not wondering about whether the latter are themselves invasive. I suppose that issue is ground for an entirely different debate among natives advocates. The points you make concerning diversity are interesting.

To me it would depend on whether the cultivar was developed by hybridizing a native with a non-native or whether it was a natural sport of a native plant. Then there are other types of cultivars:

For example, 'Savannah' holly is a cross between the native American holly and ilex cassine (also native) and some sources say "with influence from other hollies (?). Seeds from these plants (assuming they are viable) would produce plants that are different both the original sources.

Lobelia 'Ruby Slippers' is a cross between two native plants: lobelia cardinalis and lobelia siphilitica, although some the lobelia hybrids also have l. fulgens (mexican origin) as a parent.

Plants naturally hybridize themselves in the wild, however, so this may not be of too much concern. Native azaleas are known for natural hybridizing and there are now many cultivated ones also.

I personally do not support using cultivars that are derived from hybridizing with non-native plants.

A cultivar may or may not outcompete the original species. If able to outcompete by spreading vegatively, then it is only a problem in the garden. If spreading by seed, then its genes simply get mixed back into the gene pool and the cultivar will be lost in the next generation. This argument would not apply to hybrids between natives and non natives.

I do agree with esg ga that hybrids of natives with non natives would not be used by a native plant gardener.

It depends on whether one is a purist or not. A purist would not even buy seed or plants from other than his immediate vicinity let alone cultivars. A cultivar is simply a plant that has been selected for some special trait. It might be invasive if that trait was for especial vigor. As a lover of native plants years ago I tried to convince Wellsboro, PA to promote the growing of cultivars of kalmia latifolia for their Laurel Festival.

To be a "native habitat gardener" you do not need to have a large property. The consistent use of native plants (and I tend to go with the natives, not cultivars although I am not a purist) in even small spaces, such as raised flowerbeds, encourages wildlife and ecological repair to the area. "One backyard at a time" is the way we are encouraging homeowners in our area to set a little aside for the environment.

I didn't realize this topic was posted here too. I replied in the animal debates forum. So check that out if you want.

To be truly native means to come from your local area not just your state or region. It all depends on what you are trying to accomplish.