i live in the south. this spring i discovered these tall, broad-leaved, stalk-like weeds growing all in the ivy that trails up the back of my backyard. any ideas about what they are? they are everywhere. i have never seen them before, and they do not appear to be in my neighbors' yards. it seems odd, because the ivy is so thick, i didn't imagine that anything else could grown in there. any advice is welcome. thank you!