This is Asclepias purpurascens, also known as Purple Milkweed. This Rare milkweed plant does not aggressively spread out like most other Asclepias plants do, and it is considered an Endangered plant in several States. It does not spread by shooting up rhizomes everywhere. Asclepias purpurascens is the most brilliant color of any of the milkweeds. The flowers start out pink and then turn into a dark purple. This perennial is a very popular plant with the birds, bees, and butterflies. This plant is deer resistant. I do not think that they like the milky liquid inside the stems. Not only is this a larval host plant for the Monarch, Queen, and Soldier Butterflies, but it is a nectar source for many other beneficial pollinators. Growing to about 3 feet tall this plant likes to live in sun or partial shade where it blooms in the middle of the Summer. Asclepias in general are documented nectar sources for the Monarch, Orange-edged Roadside-Skipper, Dina Yellow, Carus Skipper, Eastern Tiger Swallowtail, and Falcate Metalmark butterflies. It is also the nectar source for the Clarks sphinx, and Milkweed Tussock moths. USDA Hardiness Zones 3 to 9.