Bryophyllum daigremontiana perhaps. Here is a link that might be useful:

Plumbago sort of pulls you in with it's tropical icy blue flowers that bloom almost all year, and if you forget to water it, it rewards you with more pretty flowers. When did plumbago become a noxious weed? About a year after we planted it on our slope. It's climbed over fences, completely grown over other large plants, and grown up and tangled itself through italian cypress trees more than 30 feet tall. It's popped up in neighbor's yards across the street and several houses away, just guessing by seeds, oh, those stinkin' little seeds!!! We've picked off millions of them from our skin, socks, clothes, cats, etc. If it hasn't reached your house yet, give it just a little more time. It's on it's way and will surely get there. Anyone want it for free? I'm in Walnut, near Pomona. Email me and you can come and take all you can fit in your car, and come back as often as you like, lol. Linda

They survive the winter in S.E. Ohio near house foundations. Also the seeds are viable for many, many years. I had one come up in my vegetable garden this spring. A really nice very dark-leaf one. We haven't had cannas planted for at least ten years! This is even spookier. We live in the country. Our household water source is a spring and we were excavating to install a second cachement basin. Low and behold, later that year dozens of canna lilies started coming up in and near that spot. The mystery was solved when we invited an elderly couple who live down the road to visit, because they used to live on this farm. When she saw the cannas coming up there, she said what a coincidence, her mother used to have a canna bed there. This lady was married in the 1930s. Those seeds had to have lain dormant there for fifty years at least until unearthed by the dozer.

It's definitely Linara purpurea, purple toadflax but not certain it is any named form. This perennial is very freely seeding and is almost weedy in its proliferation. Seeds piggyback in with other plants or blow in with the wind and appear almost by magic, to the point where it can naturalize widely. I have seldom seen this plant intentionally planted.