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A Comprehensive Guide to Whorled Milkweed (Asclepias verticillata)

Whorled Milkweed (Asclepias verticillata) is a herbaceous perennial that grows in most of North America except for the far western areas. This plant is a host to the Monarch (Danaus plexippus). It can grow to 3 feet tall and has green to white flowers that bloom from May to September. It is hardy in zones 3-9.

Taxonomy and Naming of Whorled Milkweed (Asclepias verticillata)

Herbarium specimen of whorled milkweed (Asclepias verticillata).
Herbarium Specimen — Asclepias verticillata L. collected in United States of America by The New York Botanical Garden (licensed under CC BY 4.0)
Lectotype of whorled milkweed (Asclepias verticillata).
Lectotype Specimen — “BM000051173” – Asclepias verticillata L. collected in United States of America by The Trustees of the Natural History Museum, London (licensed under CC BY 4.0)

Taxonomy

Whorled milkweed (Asclepias verticillata) 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, verticillata, comes from the Latin word for whorled in reference to the whorled leaves.

Common Name and Alternative Names

The common name comes from the whorled leaves. Another name, horsetail milkweed (Missouri Botanical Garden), probably relates to its resemblance another plant called horsetail (Equisetum arvense).

Physical Description of Whorled Milkweed

White flowers of whorled milkweed (Asclepias verticillata) in an open area.
Flowers of Whorled Milkweed — Mason Brock (Masebrock), Public domain, via Wikimedia Commons

Description

  • Plant Type: This plant is a herbaceous perennial.
  • Height: 1 to 3 feet
  • Stem: green and pubescent
  • Leaves: The leaves are whorled, simple, entire, and linear. They range in size from 0.5 to 3 inches in length and 0.5 inches in width. In rare cases, the leaves can be opposite (Woodson 1954). The underside of the leaves is pubescent.
  • Flower color: The flowers are green to white, sometimes with a purplish tinge.
  • Blooming period: This plant blooms from April to September. The flowers are fragrant.
  • Fruiting type and period: This plant has follicles that mature in the late summer and fall and may stay into the winter.

Range of Whorled Milkweed in the United States and Canada

Range map of whorled milkweed (Asclepias verticillata) 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 in most of North America except for the far western states and provinces. It is considered to be rare in the states of Wyoming, New York, New Jersey, Massachusetts, and Maryland. In Canada is considered to be rare in the provinces of Saskatchewan, Manitoba, and Ontario. This plant is noted to have been in Vermont in the 1800s and there is a herbarium specimen from 1914 (Eggleston 1920), but it has not been seen since.

Habitat

Roadside in Europe with wildflowers.
Roadside verge full of wildflowers by Christine Johnstone, CC BY-SA 2.0, via Wikimedia Commons

Whorled milkweed grows in open areas such as prairies, fields, meadows, pine sandhills, rock outcrops, and roadsides that have hot dry soils. It has also been documented on cedar glades (Baskin and Baskin 1978) and barrens (Henry 1985).

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). Because this plant is present late in the season, it is an important feeding plant (Bring Back the Monarchs).

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 about Whorled Milkweed

Is this plant poisonous?

Like other milkweeds, it has cardiac glycosides (cardenolides) and is considered to be poisonous with ingestion. This plant has been documented as being poisonous to livestock (Marsh 1920 and May 1920) and is likely detrimental to pets as well.

Does this plant have any ethnobotanical uses?

The Native American Ethobotanical Database notes that this species has been used for gynecological uses and for food. It also states along with the Vermont Botanical and Bird Club, that this species is used as a snake poisoning antidote (Eggleston 1920). Gardenia.net states that the seed pods are used in floral arrangements.

How is this plant distinguished from others?

This milkweed is one of the few to have whorled leaves. Another milkweed that has whorled leaves is the Woollypod Milkweed (Asclepias eriocarpa), but this plant is present only in California.

Is this plant invasive?

The NC Extension Gardener states this plant spreads by seeds and rhizomes. While not stating that is it invasive or weedy, other milkweeds with this method of spread can be weedy. However, gardenia.net says that this plant is not invasive. The Bring Back the Monarchs website, states that species can form large clones.

Is it deer resistant?

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

Gardening with Whorled Milkweed

Add Whorled Milkweed to Your Garden

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Close-up of white flowers of whorled milkweed (Asclepias verticillata).
White Flowers of Whorled Milkweed — Joshua Mayer (wackybadger), CC BY-SA 2.0, via Wikimedia Commons

Hardiness

This species is hardy in zones 3-9. 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 medium to dry soil in places it can receive full sun to part shade.

References

  • Baskin, Jerry M. and Carol C. Baskin. 1978. Plant Ecology of Cedar Glades in Big Barren Region of Kentucky. Rhodora 80: 545-557.
  • Eggleston, W.W. 1920. The Whorled Milkweed (Asclepias verticillata). Joint Bulletin of Vermont Botanical and Bird Club No. 6.
  • Henry, R.D. 1985. A Survey of Some Remnants of the Native Flora of West-Central Illinois USA. Phytologia 57: 97-106.
  • Marsh, Dwight C. 1920. The Whorled milkweed (Asclepias galioides) as a poisonous plant. Bulletin of the US Department of Agriculture no. 800.
  • May, William Lewis. 1920. Whorled Milkweed: the worst stock-poisoning plant in Colorado. Bulletin Colorado Agricultural Experiment Station 255: 1-39.
  • 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

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.

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