I believe it's Anagallis arvensis, Scarlet Pimpernel. Here is a link that might be useful: Scarlet Pimpernel

Thanks, Esh and Lycopus! I was surprised it was a Polygonum because I thought of them as "many-knees". Then I found: "Knotweed [Greek poly, many, and gony, knee joint (traditional interpretation), or gone, seed (grammatically correct interpretation)]" on efloras.org.

Be afraid, be very afraid. Herbicides won't phase it. But it looks rather nice. And it comes in white and purple. And it is a perennial that spreads underground by some of the most tenaceous roots you never want to try to dig up. And when you pull it, it comes back from the roots you leave behind. How do I dare pronounce that such a lovely plant isn't wanted? Because for over a decade I've been pulling it out of several rose beds. Season after season. Even Johnson Grass is less invasive. Morning glory- easy to control. Chickweed-dies in summer. Horsenettle will be in the bed that was originally the line of Graham Thomas Roses. It will probably still be there in 50 years. Oh, yes, one other thing. There's a potato beetle like critter whose larvae also look disgusting that will eat the leaves. But never you fear, the larvae don't eat the stems or fruit and the plant does rather well without leaves.

That's what my hubby and I have been thinking-- it sure looks an awful lot like it, and I do believe there is some sort of Phlox that grows wild around here. I've always thought of Phlox as pink, never this lovely periwinkle blue. I'm probably going to post this on the Name That Plant forum in a few days, unless anyone else here has a positive ID. Hubby just loves this flower and is as curious as I am! Gee, I'd sure love to know this cutie's name... :) Megan