Unknown Dark Clematis
It's apparently neither 'Polish Spirit' (anthers not tipped purple) nor 'Niobe' (not red enough). Its so dark purple as to be nearly black. It's been very easy to grow here. I got it from a mail order clematis place in the Napa area that went out of business, so it may have been mislabeled because they were clearing everything out in a hurry at half price all sales final, and you got what you got. What I got was a good one!