You may find some history at the link below...scroll down midway.

Here is a link that might be useful: Hibiscus mutabilis

Thanks Tulsarose for the link. It doesn't speak to the origin of Hibiscus mutabilis 'Rubrum' ( I called it "Rubrus', but think it is better known as 'Rubrum'. Some experts also now think it's a paramutabilis hybrid due to technical characteristics of its flower bud bracts and it's stipules(those little finger like green bracts that surround each bud. Stipules are those short pointy growths near where the leaf stem(petiole) joins the branch stem.
Monrovia started selling this hibiscus in the early '60's, but they don't know where this seedless variety came from. It must be a man-made or natural hybrid.

Plant Delights nursery says that ’Rubrum’ is an old hybrid of H. mutabilis x H. moscheutus. I assume ’Terri’s Pink’ is the same thing, but maybe not.

Thanks to Ethane for bringing this old thread up to the top. I think I have this hibiscus but never knew its name (thanks to palmfan). It was getting shaded out in the backyard from the neighbor's pine and sweet gum volunteers, so I dug up the two remaining plants and moved them to a very sunny location. The roots were quite thick - about as thick as a school child's forearm. I split the roots into two sections and the rest is history. Grows to 8 feet tall in a single season after pruning it to the ground in early spring.