If you haven't yet discovered the Texensis Group of clematis, do come and have a look. Though the flowers are small to medium-sized they are exquisite and, I think, some of the most elegant in the genus. 'Princess Diana' is a stunning variety with rich, deep pink, outward facing, tulip-shaped flowers with paler pink edges in July-October. During autumn and winter the plant is adorned with silky seed heads.
Woodland and stream margins, in moist humusy soils, often over limestone.