Some shady character on the market sold this to Ms. jb while my back was turned. "But it's hardy! That's what he said, anyway" "Who's "he"?" "That chappy over..... well, he was there 5 minutes ago..."[Pure fiction!. Ed.]
So we're the proud owners of a swamp hibiscus (Hibiscus semilobatus) aka Texas Star, Scarlet Hibiscus and Swamp Mallow.
Native to the USA and supposedly good up to USDA Zone 6a: -23.3°C (-10 °F).
We shall see.
Attractive while it lasted, anyway...