Comments: Three subspecies of Asclepias tuberosa are recognized by Kartesz (floristic synthesis, 1999): subsp. interior, comprising populations roughly from the Appalachian area and westwards; subsp. tuberosa, comprising populations east of the Plains states; and subsp. rolfsii, comprising populations in Florida and in adjoining states (Kartesz, 1999; USDA-NRCS 1999). The subspecific divisions are based mainly upon leaf shape, and are loosely separated along introgressive boundaries (Cronquist et al. 1984).