I had an odd weed growing out of the middle of a small hydrangea. It was tall, with a thick mottled stem, jagged-edged leaves, and lots of skinny but long thorns. It got fairly big before I caught on because it came out of the center of the hydrangea and had similar-sized leaves. Could it have been some kind of nettle? It didn't give me a skin reaction. I suspect it will grow back because I just cut it down rather than pulling it out, due to the thorns, so I'll likely get another chance to take a picture of it. It was a nasty thing!