I have a Tardiva in my garden, but I don't think this plant is a Tardiva. The blooms on my Tardiva are more airy and bloom later than the plants where I took the cutting. The blooms on my Tardiva have no smell at all. And like you, I had never noticed any smell in hydrangea blooms before either. But this particular bloom definitely had a smell to it. I need to go back to the original plants and "smell" some of the blooms on the plants. Perhaps the bloom I had was just "a bad apple" so to speak. LOL Thanks!

If it's not the native, I would get rid of it. If it is the native, it's not suitable for all gardens, a monster of a vine. IDK how to tell them apart but someone around here probably does, if that's possible from your pics. It probably can't cause any trouble in a pot, aside from dropping seeds, if that option is appealing.

I have both hibiscus and hollyhock plants (in the same family) and the leaves of thisplant does not look anything like those. However, if it turns out to be from that family, I will be happy.

Katherine, what a wonderful app ! Thanks for sharing it. It suggested loquat, Indian pokeweed, and Nouelia insignis but I'm sure it's none of those. I've submitted the pictures for review there.