This was one of the mysteries I bought last summer from a fellow that grows and sells Iowa natives. He rambled off the names of everything, but could not remember all he said. I have been trying to identify these things on my own. A few I've been able to, but this one is tricky. The top photo was taken in August, and the bottom earlier this month.

There is much variation among the flowers and leaves on this page that I am not sure it's this plant.
Wild Petunia (Ruellia caroliniensis subsp. ciliosa)

Thank you so much.

It looks like Ruella to me

Me too.

Me three?

One clue about Ruellia humilis is that it trails along the ground and the leaves are hairy.

It is that one ... humilis/ciliosa, caroliniensis, depending on what taxonomy is used.

In gardens, many times it is a thug. It spreads by seed only, but the seedlings must be dug, not pulled. Roots don't begin until an inch into the soil. The seed ejection system is pretty neat. And you need to remove seed capsules when they only have a tiny hint of browning if you want to collect or remove the crop. Seeds are ripe then.

I grew Ruella humilis from seed several years back. I love the flowers. But yes it was thug. It became very invasive. I ripped it all out. Several years later I still pull out babies that pop up everwhere on my property. Same for Verbena bonaseris.

Thank you so much for the replies. :)

We do not really have a garden, except where we plant veggies, so all natives are allowed to go where they may. At least at this point. So far, these petunias are out back in our prairie patch. I have several aggressive species in hopes they will overwhelm the non-native grasses that are already here.

We have some lawn, but that is only because we do not really want ticks near the house and the children are concerned when I talk about increasing another native patch, encroaching on their play space. But then they go play in the Giant Ragweed out in the pasture. I am sure they could live without a lawn.

Kim, I'm so glad I saw this thread because it got me to googling and reading about Ruellia and I believe that the Ruellia growing in my garden is more than likely Ruellia humilis rather than R. ciliosa, which I originally thought. This site says that R. ciliosa flowers are very pale, almost always white: http://hawthornhillwildflowers...

I'm not sure why we don't have a database entry for R. humilis because according to the Catalogue of Life it is an accepted name. I did submit a proposal to have it added to the ATP database so I'll wait to see what happens and them move my photos over.

As others have suggested, I think R. humilis is probably the one you have growing on your property:
http://www.illinoiswildflowers...

Although MOBOT: http://www.missouribotanicalga... shows it as zones 4 - 8, I believe that's an error. This USDA map shows it as native to the lower 48 with distribution in most of the central and eastern part of the U.S.: http://plants.usda.gov/core/pr...

I live in Florida where there are so many invasive plants but I haven't found this Ruellia to be bad at all. It does pop up in beds here and there and I found it in a couple of container plants but it hasn't taken over or become a pest like some plants do down here. Don't get me started on the Cashmere Bouquet (Clerodendrum bungei) plant!! I mowed the lawn today and mowed a lot of that down ... a few months ago we yanked and dug so much of it out but it travels by runners beneath the soil and pops up fifteen and twenty feet or more away from the original planting.

For comparison, this is the Ruellia I have:

The lack of a Ruellia humilis page is one of several things that threw me off when trying to ID this. Thank you for submitting a proposal to create one. Your Ruellia has a nice color. Purple is my favorite.

Your Cashmere Bouquet sounds as bad as my Creeping Charlie. I was so distraught when I found it in my prairie patch. I hope the natives can snuff that one out, but I am not sure. That first planting was done differently than we would probably do for our other areas. It was all exposed soil from some construction work we had done, so wide open for every good and bad seed out there. I am grateful for every native plant back there.

This last year, we read you can actually seed over existing growth and in time the native plants will take over. Our pasture is largely brome grass. Way in the north part, some Asters, Hoary Vervain, Milkweed have popped up. Oh, I like that purple of the Asters! We didn't plant those, so that is a real treat. We learned that a neighbor to the north had planted some native seeds in the back portion of his property, so I suspect some has drifted our way.