Clematis alpina. Strong growing, amazingly tough varieties that can withstand temperatures down to -40, they grow in areas/places and countries that other clematis just cannot. They naturally grow up in the mountains hence the fact that they never need pruning ( or any looking after for that fact ) they thrive on neglect! The alpina varieties flower from March to Mid May with hundreds of nodding flowers ( mainly 4 sepals, but some can have more, varying in length ) then they have fantastic seed heads for the rest of the season, that creates interest for some time after the flowers have gone. Clematis alpina  can be grown in any aspect and can also be grown in tubs/pots or planters if you wish ( so very versitile )