This is one tough little beauty. Delicate, elegant, yet an 'ironside', as they would say in 'ye olde English'. You would have to try hard to kill it...
This is one of the earlier Russian Clematis integrifolia (herbaceous clematis) hybrids from 1963. Exceptionally hardy, disease-free and low-maintenance. Just like all Integrifolia hybrids, it flowers on current year's growth, so it has to be hard pruned to the very ground every spring. Which means that it can be successfully grown in cold areas, and there is no need to cover it for winter.
One thing to remember though is that this clematis is non-clinging. When it starts off in spring, it clings a little to any support it can find. But later on it becomes top heavy under the weight of foliage and abundant flowers, and just flops onto whatever is growing close to it. In my garden it happens to be Hydrangea arborescens 'Annabelle' (and I am quite happy with the combination). So if you want to grow it upright you'd better make sure it is grown next to an appropriate support (for example, an obelisk). Alternatively, it can be grown draped over the ground or over low growing conifers. Unfortunately, my garden is absolutely flat, so I still haven't worked out where to place it. But for someone who gardens on a slope or has a decently-sized alpine garden this is a perfect plant to try, where it will cascade weaving its flowers around rocks and alpine plants without smothering them.
Here is a picture, which shows the idea. This is a different clematis variety, 'Arabella', but it works the same way, more or less. Doesn't it look great? http://www.clematisinternational.com/japan2008214.jpg