Weed, or someone's run away?
Two years ago I had this plant spring up on the outside of my back yard. I saved some seeds because I thought it a pretty flower.
I didn't plant any last year and no signs of it anywhere so I assumed it was an annual.
This year, I still didn't plant the seeds and this plant sprouted everywhere across my back fence.
It's obviously a toughie, growing in dense clumps of weeds and some plants looking close to 6' tall.
It looks familiar but what I'm thinking of, which I can't remember the name, is not known for growing tall.
It does seem to grow from a clump with multiple stems.