Purple milkweed

This perennial forb, scientifically known as 'Asclepias,' is named after the Greek god of medicine, Asklepios, reflecting its historical medicinal use. The word ‘purpurascens’ is a Latin term meaning “becoming purple” or “turning purple”.

The common name, Purple milkweed, is quite descriptive, as this plant bears large clusters of vibrant purple flowers.

A mature plant will have many flower clusters, with some having green to reddish buds while other flowers are completely open. The beautiful buds are initially green, transitioning to a peachy color with purplish stripes along the unopened buds.

Flower clusters occur at the top of the central stem with up to 5 or 6 umbels. Individual umbels are large, with a width of 2-3 inches. The color varies from light to dark purple.

This perennial native plant typically grows to a height of 3 to 4 feet. The light green stem is unbranched (or may branch at its top). It often has a vertical line of hairs at the stem center, although it may be hairless. If the stem is broken, the sticky, milky substance associated with milkweeds can be seen leaking from the break. This sap is toxic to many animals (and also irritates the skin and eyes of humans). The photos below show examples of the variable stem pubescence.

Leaves are opposite with short petioles and up to 6 inches long with a central vein.

Asclepias purpurascens is known to have highly variable growth year to year with formation of seed pods and seed set being sporadic. Some pods start to form but never fully develop. Consequently, this species is rare in parts of its range being listed as Endangered, Threatened, or Imperiled (see Conservation Status below).

Not only are the flowers of Asclepias purpurascens beautiful, they support a wide range of insects. Numerous bumblebees, sweat bees, butterflies, skippers, bee flies, and even hummingbirds visit the flowers of Purple milkweed for nectar. In addition, it is a host plant for the caterpillars of the Milkweed tussock moth that feed on its foliage.

Butterflies and Skippers

In addition to the butterflies shown above, Monarch, Pipevine Swallowtail, Giant Swallowtail, Red Admiral, Eastern Tailed-Blue, and Regal Fritillary butterflies have been documented visiting the flowers.

Another unusual visitor to the flowers is the Ruby-throated Hummingbird.

Bees

Other

In addition, Purple milkweed is a host plant for Milkweed tussock moth. These fuzzy, colorful caterpillars are fun to watch as they munch on the leaves.

Purple milkweed does well in woodland edge and savanna habitats where it gets dappled sunlight. It thrives in oak-hickory savannas. It is also found at the edges of prairies adjacent to wooded spaces and in glades.

While NatureServe categorizes Asclepias purpurascens as G4, indicating its overall status as Apparently Secure, only two of the 33 states within its range are currently depicted as Apparently Secure.

The current status of the species is as follows:

SH (Possibly Extirpated)- Mississippi, New Hampshire, Rhode Island

S1 (Critically Imperiled)- Georgia, Louisiana, Massachusetts, Oklahoma, Tennessee, S1? North Carolina

S2 (Imperiled)- Delaware, Maryland, Michigan, Nebraska, Wisconsin

S2/S3- Connecticut, New York

S3 (Vulnerable)- Iowa, Kansas, Kentucky, New Jersey, Virginia

S3S4- Indiana

S4 (Apparently Secure)- Pennsylvania, West Virginia

SNR (No Status Rank)- Alabama, Arkansas, Illinois, Minnesota, Missouri, Ohio, South Dakota, Texas

SX (Presumed Extirpated)- District of Columbia

In Arkansas, Asclepias purpurascens has a C-value of 7 in the group of 4-7 meaning “Typically matrix taxa in intact, stable habitats, with some limited ability to respond to destabilizing forces and repopulate areas from which they have been extirpated.”

Mammals tend to avoid consuming the leaves of Purple milkweed (along with other milkweeds) because the foliage contains toxic cardiac glycosides that have a very bitter taste. Hence, we can enjoy the plants in our gardens without worry they will be dinner for the deer!