I second the Clidemia spp. I had been growing that for many years and aways had thought it was a Clidemia, as it usually grew to a height of several feet in a matter of months. However, recently many people have been growing something under the name Bertolonia sp. 'Itatiaia', and all photos look similar. I would say that most of these are definately Clidemia if they grow past a foot or two. Clidemia is a tall, fast growing streamside weed. Mine right now is at least 24" tall. I've never had any Bertolonia grow fast or tall, actually it usually craps out on me.