Gardens and Arboreta
This unfortunately quite short list contains links to the public gardens and arboreta in the US and around the world where you can see the native Clematis in subgenus Viorna.
Delaware:Mt. Cuba Center, located in northern Delaware, is a non-profit institution that focuses on the flora of the Appalachian Piedmont. Native clematis species presently found in the woodland wildflower gardens include Clematis addisonii, C. glaucophylla, C. ochroleuca, and C. viorna, with additional species planned for the future. Admission to the garden is by advance reservation only. To make a reservation, please visit www.mtcubacenter.org
The Scott Arboretum
Virginia:Green Spring Gardens
Denmark:Hans Jørgen Kuus, Stolbrogade 22, 6430 Nordborg. Phone +45 74458068.