THis is its seed pod...there were lots of these spiny pods and millions of seeds.
The plant itself has a big thick hollow stem, gets about 5' tall here, and has little trumpet shaped flowers. It was interesting, but I have no idea where it came from and given the vigorous growth and huge seed production, fear that it is an invasive.
I had them( white ones) reseed for a few years, then they never came back:( I don't think they will go wild on you & the babies are easy to move or get rid of if you do it early. My sister hated them popping up all over, I liked it. :)Anita