Torenia.

Rhexia mariana perhaps? I'm not real happy with that ID because it looks more like Melastoma/Dissotis to me but they aren't listed as naturalized in North Florida?

WOW!! That is it! I have searched all summer to find out what that plant is. I love flowers but I am not plant savvy with all plants. That is it!! Thank you!!!!!!!!!!! But what I am reading is that this is native to Missouri and grows in waste land. I live in OHIO and in a nice neighborhood and no waste land around not even a new home being built. Where did this come from? And where it was growing I have put flowers in every year for the past 11 years and have never seen this before. I can't tell you enough times thanks. It is really a beautiful flower and I had planned on tossing some of the seeds in the back of our property at work. There is a very large wooded area and I have been tossing some of my flower seeds this year to see if any of them will grow next year. So far 1 single pink malva has sprouted up and over and around a large patch of jewel weed and bloomed a few buds to end this season. I have tossed Cosmos, Zinnias, and pink Malva, plus some Echinacea. We feed the birds and the squirrels. There are butterflies and hummingbirds too. And I thought that this yellow flower might like to grow along some of the trees since it seemed to tolerate shaded areas. Thanks again for your help.

Wow, you people have such an experience with it. I love that plant and while it does spread around a bit it is nowhere close to being the pest you describe! This year was first year I actually dug out few pieces to give away after having it for 3 years. It is not hard to remove where I do not want them either. I also have variegated lyshimachia Alexander which also behaves. Again my garden is informal so I really do not care if they do not form clump or migrate a little, have not noticed them migrating more than couple of feet from original placement. Maybe it is because I grow them in the shade but have not had any problems from them. I have bed of lysimachias, tiger and asiatic lilies,aconitums, macleya cordata, corydalis lutea which reseeds like crazy but very happy and blooms all summer and dwarf yellow and variegated bamboo. Those ones do try to get into walking path grass but not invasive enough due to being not fully cold hardy here. Out of all of the only bamboo is kind of hard to dig up.