This is smartweed. You gotta love that pink, even though it's a pretty invasive weed.
The Latin is Polygonum cespitosum. There are a bunch of smartweeds. Here's a site that describes a bunch of them.
The bees love that pink. I was pleasantly surprised to see the bees all over it this fall so I'll be less likely to totally eradicate it next year. It's an important late season nectar plant.
It is a perennial and it will take over so I'm pondering ways of giving it some space, but not all of the space. I'll let you know what I come up with.
