Several years ago I first noticed this exuberant, large leaved plant growing along the road I commute on every day. It kept growing, and growing and growing! Finally these huge umbels developed looking just like gigantic Queen Anne's Lace.
I was in love.
It was easy to look up. Just query "9 foot tall plant looking like Queen Anne's Lace on steroids"! Heracleum maximum , giant cow parsley.
Another description I saw was " looks like Queen.Anne's Lace with an attitude".
I stopped later in the year and gathered the seed which I threw everywhere around my house hoping in would be happy somewhere. One plant grew. (and grew, and grew...)
It comes back every year and there is a younger plant now growing near it. The dryness of my property keeps it in check.
Update, July 2015: Finally, a new plant seeded itself next to the house! It was hiding behind a pile of kayaks and when I put them in the newly built shed, there it was! I go around each fall flapping the giant seed head like a fairy wand hoping it would find additional spots. This year the original plant was short. I wonder why.