I believe it is zone 7b. The weather is quite moderate most of the time.I looked at the USDA plant database for those plants.
Native ... in some places in the US. But, the one mentioned elsewhere as a garden plant is a native perennial in Louisiana and environs.
Gosh. It just goes to show how maritime Washington is so warm through the winters, if'n it's growing as a perennial there! What do you suppose your winter hardiness zone is, Dahlia?