This is called Mulberry Weed. It's relatively new in our area and can go like gangbusters in the shade. It is an annual that will die with the frost, but try to stop it from going to seed. It doesn't really get a flower that is noticeable, but has purplish puffball-looking flowers.
It's really easy to pull, but get it from the root or it will grow back with multiple shoots that will bloom lower.
Look for it in spring and rake or pull the new plants.
Here is a page about it: https://www.invasive.org/weedcd/pdfs/mulberry.pdf