Some years ago I grew from seed something that was labelled Clematis integrifolia. It clearly wasn't, since it galloped straight to the top of a Sorbus. So I've been looking out for flowers, and this year I spotted them at the top of the tree - white, dropping, with rounded rather than pointed petals. In terms of flowering time, this is very early - before C armandii, and before CC alpina is even showing buds. So I assume C cirrhosa - but is there anything else it could be?

It's also not totally tender - it's come through this winter unscathed, whereas I lost my 10 year old C armandii