This is a horticultural (domestic) clematis species. Another of the buttercup or Ranunculaceae family of plants. This one taken at Missouri Botanical Garden May 2017.
The genus is composed of mostly vigorous, woody, climbing vines / lianas. The woody stems are quite fragile until several years old. The genus name is from Ancient Greek clématis, (“a climbing plant”). Over 250 species and cultivars are known, often named for their originators or particular characteristics. Wikipedia