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A Comprehensive Guide to Side-Cluster Milkweed (Asclepias lanuginosa)

Side-Cluster Milkweed (Asclepias lanuginosa) is a herbaceous perennial that is native to the mid-western United States and Canada. This plant is a host to the Queen (Danaus gilippus) and Monarch (Danaus plexippus) butterflies. Growing from 0.5 to 4 (6) feet tall, this species has green to cream flowers that bloom from May to July. It is hardy in zones 4-7.

Taxonomy and Naming

Herbarium specimen of side-cluster milkweed (Asclepias lanuginosa).
Herbarium Specimen — Asclepias lanuginosa Nutt. collected in United States of America by The New York Botanical Garden (licensed under CC BY 4.0)

Taxonomy

Side-Cluster Milkweed (Asclepias lanuginosa) was originally named and described by Thomas Nuttall, an American botanist, in 1818. Over the years it has been described and renamed, but it still officially has its original name. The species has kept this name since this time and is a member of the Dogbane Family (Apocynaceae).

Meaning of the Scientific and Common Names

Scientific Name

The genus name, Asclepias, is named for the Greek god of healing, Asklepios (Flora of Wisconsin). The species name, lanuginosa, means “woolly” in Latin. This name is apparently referring to the woolly (hairy) nature of the plant.

Common Name and Alternative Names

The common name comes from the position of the flowers. Other common names for this plant include woolly milkweed, not to be confused with the other woolly milkweed (Asclepias vestita) and hairy milkweed.

Physical Description

Plant of side-cluster milkweed (Asclepias lanuginosa).
Plant growing in a field — Asclepias lanuginosa Nutt. observed in Canada by Chris Friesen (licensed under CC BY 4.0)
  • Plant Type: This plant is a herbaceous perennial
  • Height: 0.5 to 4 (6) – (Budd’s Flora 1987) feet
  • Stem: The pubescent stem is spreading to ascending and not branched.
  • Leaves: The leaves are alternate or maybe opposite, short-petiolate, simple, entire, and ovate to lanceolate in shape. The leaves are 1 to 3 inches long and about 0.4 to 2 inches wide.
  • Flower color: green to cream
  • Blooming period: This plant blooms from May to August.
  • Fruiting type and period: This plant has follicles that mature in the late summer.

Range of Side-Cluster Milkweed (Asclepias lanuginosa) in the United States and Canada

Range map of side-cluster milkweed (Asclepias lanuginosa) in the United States and Canada.
Range Map Credit: Kartesz, J.T., The Biota of North America Program (BONAP). 2023.(website https://bonap.org/). Chapel Hill, N.C. [maps generated from Kartesz, J.T. 2023. Floristic Synthesis of North America, Version 1.0. Biota of North America Program (BONAP). (in press)]

This milkweed species is native to the mid-western United States and Canada. It is considered to be rare in all of its range except for the state of Minnesota.

Habitat

Prairie habitat in United States.
Prairie Habitat — USFWS Mountain-Prairie, Public domain, via Wikimedia Commons

This species grows in prairies and sandhills.

Hosted Insects

Queen Butterfly on Twig.
Queen Butterfly (Danaus gilippus) — Korall, CC BY 3.0, via Wikimedia Commons

Other Supported Wildlife

Bumblebee on pink flower.
Pink flower with Bumblebee — Joaquim Alves Gaspar, Public domain, via Wikimedia Commons

This species is a nectar source to other butterflies, skippers, bees, and wasps during the growing season. Birds also like this plant.

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 plant specifically, but milkweeds in general have been used for pharmaceuticals, foods, and fibers.

How is this plant distinguished from other milkweeds?

This species is similar to green comet milkweed (Asclepias viridiflora), but green comet milkweed several lateral umbels, whereas this species milkweed has a solitary umbel that is terminal (Budd’s flora 1987).

Is this plant invasive?

This plant has not been shown to be invasive in the literature.

Gardening with Side-Cluster Milkweed (Asclepias lanuginosa)

Plants of side-cluster milkweed (Asclepias lanuginosa) with white flowers.
Plant of Side-Cluster Milkweed — Asclepias lanuginosa Nutt. observed in Canada by Chris Friesen (licensed under CC BY 4.0)

Hardiness

This species is hardy in zones 4-7. 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. However, if planted outside of its range, the hosted species may not recognize the plant or be harmed by ingesting a different species with an unfamiliar chemical composition.

Optimal Conditions

This species grows best in places that have full sun and well-drained soils.

References

  • J. Looman Research Station. 1987. Budd’s Flora of the Canadian Prairie Provinces. (Ottawa: Agriculture Canada).
  • 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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