Hilary, if you take a closer look at those fluffy seedballs now, you should be able to see if it's a Clematis vitalba or C. flammula. The first one produces more fluff than C. flammula, but even the latter one has very feathery seedballs, see the first of the photos, but the seed itself of C. flammula is much bigger (second photo) than that of C. vitalba (third photo), which has longer feathery appendixes.