Looks like a type of Desmodium.

Clematis terniflora (sweet autumn clematis) seedling

Yes - SAC.

I think you guys are right. Very aggressive vine.

It shares a large area with blue mist flower, sedum, Russian sage, Black-eyed Susans, etc under a pear tree. Most of them done flowering for the season. I'm inclined to leave it, but monitor it's activity closely.

I LOVE my clematis terniflora. HOWEVER...I now have four LARGE specimens, which started as one small plant, about 15 years ago. It is a rambunctious grower, and it DOES seed about. You'll notice I was very familiar with the look of the seedlings, lol. But so far all the seedlings have popped up fairly close to the parent plant (no farther than my back yard). I live on 110 acres, and none have showed up in fence row or woods YET (fingers crossed and eyes open). Do keep an eye on it; I know in some places it's invasive. But it's a lovely late summer bloomer, which smells like a combo of vanilla and grape to me.