Please help! I've been told there are 2 kinds of clematis that have little, white flowers in the autumn. I've been told that one is a native to North America. I've been told that the other is a non-native invasive. How can I tell them apart? The one I have is seeding all over the place, so is it the non-native invasive?

Thanks very much- I have enjoyed reading the previous threads, there seems to be a lot of good gardeners in this forum.