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A Comprehensive Guide to Purple Milkweed (Asclepias purpurascens)

Purple Milkweed (Asclepias purpurascens) is a herbaceous perennial that grows from the mid-west to eastern North America. This plant is a host to the Monarch (Danaus plexippus). It can grow to 6 feet tall and has pink, red (rose), to purple flowers that bloom from May to July. It is hardy in zones 3-8.

Taxonomy and Naming of Purple Milkweed (Asclepias purpurascens)

Herbarium specimen of purple milkweed (Asclepias purpurascens).
Herbarium Specimen — Asclepias purpurascens L. collected in United States of America by The New York Botanical Garden (licensed under CC BY 4.0)
Type specimen of purple milkweed (Asclepias purpurascens).
Type Specimen — “Asclepias purpurascens L. (Ваточник), Moscow University Herbarium” – Asclepias purpurascens L. by Moscow State University (copyright is managed by Dr. Alexey P. Seregin) (licensed under http://creativecommons.org/licenses/by/4.0/)

Taxonomy

Purple milkweed (Asclepias purpurascens) was named and described by Carl von Linnaeus, in Species Plantarum (1753). It has kept this name since. This plant is a member of the Dogbane Family (Apocynaceae).

Meaning of the Scientific Names and Common Names

Scientific Name

The genus name, Asclepias, is named for the Greek god of healing, Asklepios (Flora of Wisconsin). The species name, purpurascens, comes from the Latin word for purple, referring to the color of the flowers.

Common Name and Alternative Names

The common name comes from the color of the flowers. A review of the literature has revealed no other common names in use.

Physical Description of Purple Milkweed

Plants of purple milkweed (Asclepias purpurascens).
Purple Milkweed Plants in a Garden — peganum from Henfield, England, CC BY-SA 2.0, via Wikimedia Commons
  • Plant Type: This plant is a herbaceous perennial.
  • Height: 2 to 6 feet
  • Stem: glabrous (hairless) when mature, short-hairy when young
  • Leaves: The leaves are opposite, simple, entire, and ovate to oval or lanceolate. They range in size from 2 to 7 inches in length and 1 to 4 inches in width. The margins are undulate.
  • Flower color: The flowers are purple, deep rose to pink in color. The flowers may start out as pink, but become a deeper purple as they mature (Wikipedia).
  • Blooming period: This plant blooms from May to July.
  • Fruiting type and period: This plant has follicles that mature in the late summer and fall.

Range of Purple Milkweed in the United States and Canada

Range map of purple milkweed (Asclepias purpurascens) in the United States and Canada.
Kartesz, J.T., The Biota of North America Program (BONAP). 2015. North American Plant Atlas. (https://bonap.net/napa). Chapel Hill, N.C. [maps generated from Kartesz, J.T. 2015. Floristic Synthesis of North America, Version 1.0. Biota of North America Program (BONAP). (in press)].

This species grows from the mid-west to the eastern United States and Ontario in Canada. It is considered to be rare in most of the states where it occurs. These states include Nebraska, Minnesota, Wisconsin, Michigan, New York, Massachusetts, Maryland, Delaware, Virginia, Tennessee, North Carolina, Georgia, Mississippi, and Louisiana and the province of Ontario in Canada.

Habitat

Riverine floodplain forest in Delaware.
Floodplain Forest — Author Image

Purple milkweed grows in places that have full sun or part shade such as swamps, woodlands, meadows, bottomlands, roadsides and dry fields (Angelo and Boufford 2013) and thickets. This species can be an indicator of oak savannas (Brock 2009).

Hosted Insects

Monarch butterfly on green flower.
Green Flower with Monarch Butterfly — U.S. Fish and Wildlife Service, Public domain, via Wikimedia Commons

This species is a host for the Monarch Butterfly (Danaus plexippus) and maybe also the golden banded-skipper (Autochton cellus) (Calhoun 1985). Monarchs appear to show a preference for this species in particular if found and may be a contributing factor to the plants rarity (Brock 2009).

Other Supported Wildlife

Wood thrush on branch.
Wood Thrush — Andy Reago & Chrissy McClarren, CC BY 2.0, via Wikimedia Commons

This species produces abundant nectar and is used by other butterflies, bees, beetles, and birds in the late summer and fall.

Frequently Asked Questions

Is this plant poisonous?

Like other milkweeds, it has cardiac glycosides (cardenolides) and is considered to be poisonous with ingestion.

Does this plant have any ethnobotanical uses?

The Native American Ethobotanical Database does not mention this species specifically, but in general milkweeds have been used for foods, fiber, and pharmaceuticals.

How is this plant distinguished from others?

This milkweed is similar to the common milkweed (Asclepis syriaca), but the flowers of purple milkweed have a deeper pink-rose color (Missouri Botanical Garden). The hood margin on the common milkweed has a sharp tooth, whereas the purple milkweed does not. These two species can hybridize between each other (Rintz 2014). The Midwestern wetland flora field office guide to plant species, states that purple milkweed is the only milkweed to have “completely red-purple flowers and stalked leaves” (Biotic Consultants 1997).

Is this plant invasive?

The Missouri Botanical Garden and NC Extension Gardener both state that this plant can be weedy. However, some other sites say that the plant is not invasive.

Is it deer resistant?

This species is considered to be deer resistant and is likely a result of the toxins in the stem and leaves.

Gardening with Purple Milkweed

Add Purple Milkweed to Your Garden

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Close-up of pinkish-purple flowers of purple milkweed (Asclepias purpurascens).
Flowers of Purple Milkweed — Steepcone, Public domain, via Wikimedia Commons

Hardiness

This species is hardy in zones 3-8. If your garden is within these zones and you have the right growing conditions (soil, moisture and exposure), you may well be able to grow this plant.

Optimal Conditions

This species grows best in moist soil where it can receive full sun to part shade, though more shade is preferred (Wikipedia). It likes moist, well-drained soil if possible but also occurs in dry woods.

References

  • Angelo, Ray and David E. Boufford. 2013. Atlas of the Flora of New England: Families of Vols. 6 & 14: Flora of North America. Phytoneuron 2013-45: 1-23.
  • Biotic Consultants – Midwest National Technical Center. 1997. Midwestern wetland flora field office guide to plant species. Lincoln, NE: USDA Soil Conservation Service.
  • Brock, Thomas D. 2009. Ecology and Conservation of Purple Milkweed (PDF). Published in Ecological Restoration 27(3)
  • Calhoun, John V. 1985. An Annotated List of the Butterflies and Skippers of Lawrence County, Ohio. Journal of the Lepidopterists’ Society 39(4): 284-298.
  • Rintz, Richard E. 2014. A naturally occuring hybrid between Asclepias syriaca L. and A. purpurascens L. (Apocynaceae, Asclepiadaceae). Phytologia 96(2): 130-134.
  • Woodson, Robert E. 1954. The North American Species of Asclepias L. Annals of the Missouri Botanical Garden 41: 1-211.
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Robert Coxe

Robert Coxe is a professional ecologist and botanist who has worked as the State Ecologist of Delaware and as an ecologist for the Western Pennsylvania Conservancy. He is also a former Past-President of the Pennsylvania Academy of Science. He currently is an innkeeper at McMullen House Bed & Breakfast LLC and a web designer and owner for Silphium Design LLC.