I don't know what it is, but it's very prolific. I didn't have it, then one year I had many sections of it in my pasture. Now I have it all over my 1 acre property. On close inspection, the seed pods are little balls with 'grabbers' on them. I think cats and birds get it stuck to them and drop the seeds all over the place. I've tried digging them out, but they're so prolific it has soon gotten out of control. It's not something the animals will eat.