I doubt very much that Carissa was grafted. Mostly likely grown from cuttings. So, either these are seedlings or they are root suckers that have reverted to the wild form of cornuta. Are there any other cornuta around? Carissa is not really know for berry production, I don't believe. I could be wrong.

Thanks for your thoughts, Dave! And I think you're right. I did quite a bit of digging and I never could actually find a spot where the cornuta was actually conjoined with the Carissa. I DID find some new cornuta around as if it were springing up on its own, some of it sending out rhizomes (I think that's what it's called?) that more plants were sprouting from. But worse: there is plenty of cornuta entwined with the Carissa- some with stalks thicker than my thumb.

I'm guessing someone must have planted the Carissa without ever fully removing the cornuta? Or else it's what you said: root suckers that have reverted to the wild form (I don't know what that means, by the way, but I'd love to hear more.)

Either way, how will I get rid of it? If the plants are separate, I imagine I can use chemicals to kill the cornuta, as much as I hate the thought. But if it's reverted root suckers like you said, will I end up killing my dear Carissa with chemicals? And how will I know?

Thanks so much for your thoughts!