I think it is Germander (Wood-sage) Teucrium canadense. This is a widespread and variable North American species. If not that species, it is very definitely a Teucrium, since it has only the lowest lobe with any size to it.

Here is a link that might be useful: Germander (Wood-sage)

Thank you. My wild volunteer isn't quite as showy, but I think you're right. Appreciate the help.

It looks like Florida Betony (Stachys floridana) to me. If you are in Florida or the more coastal/warmer parts of the Southeastern US it is very likely. If so, it is said to be extremely invasive and hard to control so you may want to do some research. If you carefully dig up a plant and find a tuber that looks like a white grub or a white rattlesnake tail, then you have Stachys floridana.

I had some of the tubers hitchhike with some Crinums that I transplanted from south Georgia. Luckily, I found the tubers and got an I.D. before unleashing it in my yard.

I hope that helps even if it's not the happiest of news.
:)

Yep, it does have those underground tubers. I'll see if I can remove it today before it spreads much further. It's in loose dirt, so i should be able to get it out. It's too bad it's so invasive. I'm fighting a trumpet vine right now, so I'm not in the mood for any more invasive plants. Thanks for your help.

Yes, it is too bad that it's so invasive as it's a rather cute plant. The tubers are said to be edible and rather tasty too but I've never tried them.