Why do you say the flowers are not sessile?

Maybe I don't understand what I'm seeing, but there is definitely a stem between the bottom of the flower and the primary stem. I thought that the bottom of the calyx would sit in the leaf axil if sessile??

Now I could be wrong too, but to me, I would not consider that to be a petiole. I had a Carolina one growing out front, so here is a snap of it's arrangement.

Your photo looks right for Carolina Petunia. Now compare with my flower and that non-sessile pedicel or peduncle underneath. They seem different to me.

I don't know Ruellia very well since we don't get them here, but I wonder if it matters if you interpret the base of the pedicel as being subtended by leaves or bracts. From the base of the leaves/bracts the pedicel can't be more than a few mm long.

Lycopus, I checked with the Missouriplants.com site, since they always have good descriptions and photos. The typical R. pedunculata specimen has single axillary flowers on bracteate peduncles, and a pair of foliaceous bracts subtend the calyx. So those small "leaves" under the calyx in my photo are the bracts. The distance on my plant from the bracts to the leaf axil is about 0.25 inch long - not sessile, but too short for R. pedunculata.

In any case, the main reason for this post was to see if anybody was familiar with R. purshiana, and if that could be a match.

Thanks for the comments.

Here is a link that might be useful: Ruellia pedunculata