Ask Mr. Smarty Plants

Clematis x jackmanii is a result of many hybridizations since the mid 1800's, and therefore will not appear in our Native Plant Database. We will look at a clematis native to Indiana to learn some of its traits. There are 3 members of the Ranunculaceae (Buttercup) family that grow natively in Indiana. These are:

Clematis pitcheri (Purple clematis)

Clematis viorna (Vasevine)

Clematis virginiana (Devil's darning needles)

Then we searched our database for petunias. Actually, we already know that the petunia native to North America is not likely to be the one you have in your garden. If you bought bedding plants in a large nursery, the petunias are hybridized many times over for shape and color, and originated in South America.  In botanical classification, tobacco, tomato, potato, and petunia are all in the family Solanaceae. There are about 35 species in the genus

There are 3 species of the native petunia native to Indiana, all members of the genus Ruellia and family Acanthaceae (Acanthus):

Ruellia caroliniensis (Carolina wild petunia)

Ruellia humilis (Fringeleaf wild petunia)

Ruellia strepens (Limestone ruellia)

So, to summarize, you are asking if members of the genus Petunia (non-native, family Solanaceae or the genus Ruellia (native petunia, family Acanthaceae) could cross breed with members of the native Clematis genus (family Ranunculaceae.)

The female flowers of each crop can be fertilized only by pollen from male flowers of the same species. So, we are looking at three different genera, families and species. Won't work.

If you study some of the information on the petunias and clematis, you will note they have many different forms, especially those that have been hybridized. It would seem that the similarities in your petunias and clematis are completely coincidental.