Suggest you send the image to your county's Extension Service office as they're likely to know what's common in your region.

Locate your county's office with this map:
http://www.csrees.usda.gov/Extension/

Here is a link that might be useful: locate your county's Extension Service office

Try the name That Plant forum.

Here is a link that might be useful: Name That Plant

Does it have an herb-ish odor? Maybe Lantana. If that's not it, compare it to Three-seeded Mercury, Acalypha rhomboidea. Sure looks familiar, I know I've pulled some of that up.

Could it be Lantana?