Sweet potato vine.
When I bought a crape mytle 3 summers ago, a tiny spring of this was growning in the pot.
By the end of that summer, it covered the entire garden.
I did my best to pull it all up, but in the Spring it came right back.
Last Summer I just dealt with it, keeping it in check by pruning back it seemed constantly.
This year I finally got it all up and out.
You just can't kill it.
Oh, don't get me wrong, it's very pretty, and I like it. It just wasn't in my plans for my garden, since it's small. It will just take over.
It has dark dark purple leaves, the new growth is bright green. The underside of the purple leaves are a different color, and it was enchanting when a breeze would flutter them around.