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A Comprehensive Guide to Woolly Milkweed (Asclepias vestita)

Woolly Milkweed (Asclepias vestita) is a herbaceous perennial that is native to the state of California in the United States. This plant is a host to the Queen (Danaus gilippus) and Monarch (Danaus plexippus) butterflies. Growing from 1.5 to 3 feet tall, this species has cream to yellow flowers that bloom from April to June. It is hardy in zones 7-10.

Taxonomy and Naming of Woolly Milkweed (Asclepias vestita)

Herbarium specimen of woolly milkweed (Asclepias vestita).
Herbarium Specimen — Asclepias vestita Hook. & Arn. by The New York Botanical Garden (licensed under CC BY 4.0)
Isotype specimen of woolly milkweed (Asclepias vestita).
Isotype Specimen — Harvard University Public Domain

Taxonomy

Woolly Milkweed (Asclepias vestita) was originally named and described by William Jackson Hooker and George Walker Arnott, both UK botanists, in 1839. 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, vestita, comes from the Latin word, vestitus, which means clothed in hairs. This name is apparently referring to the woolly (hairy) nature of the plant.

Common Name and Alternative Names

The common name comes from the fuzzy or woolly feel of the leaves.

Physical Description

Pink flowers of woolly milkweed (Asclepias vestita).
By Alex Heyman no rights reserved
  • Plant Type: This plant is a herbaceous perennial.
  • Height: 1.5 to 3 feet
  • Stem: The stem is ascending to decumbent and is pubescent when young, but becomes glabrous with age (Woodson 1954). The plant has been described as floccose-woolly (Gray 1878).
  • Leaves: The leaves are opposite (whorls of 2), short-petiolate, simple, entire, and ovate to lanceolate in shape. The leaves are 1.5 to 6 inches long and about 1 to 2 inches wide. Leaves can be semi-succulent (Woodson 1954).
  • Flower color: yellowish-white or greenish-white with a purple tint
  • Blooming period: This plant blooms from April to July.
  • Fruiting type and period: This plant has follicles that mature in the late summer.

Range of Woolly Milkweed (Asclepias vestita) in the United States and Canada

Range map of woolly milkweed (Asclepias vestita) 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 state of California in the United States.

Habitat

Desert habitat in southwest.
Desert Habitat — Patrick Alexander from Las Cruces, NM, CC0 1.0, via Wikimedia Commons

This species grows in dry plains, canyons, and chaparral.

Hosted Insects

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

This species is a host for the Monarch Butterfly (Danaus plexippus), the Queen Butterfly (Danaus gilippus) and possibly the White-lined Sphinx (Hyles lineata) and the Isabella Tiger Moth (Pyrrharctia isabella) (Calscape.org).

Other Supported Wildlife

Metallic bee on white flower.
Flower with Metallic Bee — David Whelan, CC0, 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. This plant has been described as being poisonous to livestock (Las pilitas).

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 most similar to indian milkweed (Asclepias eriocarpa), desert milkweed (Asclepias erosa), and the Mojave milkweed (Asclepias cryptoceras). The Mojave milkweed has corolla lobes that are more than 10 mm long, whereas woolly milkweed is shorter 10 mm. The other two species have peduncled umbels, whereas this species does not. As a group all of these species have pedicels that are deflexed in fruit (Abrams 1951). California milkweed (Asclepias californica) has been described as being similar to this plant, but the subject species has a more gray-green foliage and shorter petioles (mariposanativeplants.com).

Is this plant invasive?

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

Gardening with Woolly Milkweed (Asclepias vestita)

Plant of woolly milkweed (Asclepias vestita) in the desert.
Plant of Woolly Milkweed — Asclepias vestita Hook. & Arn. observed in United States of America by Kimball Garrett (licensed under CC0 1.0)

Hardiness

This species is hardy in zones 7-10. 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

  • Abrams, Le Roy and Roxanna S. Ferris. 1951. An illustrated flora of the Pacific States: Washington, Oregon, and California. (Stanford University: Stanford University Press).
  • Gray, Asa. 1878. Synoptical flora of North America. (New York: American Book Company).
  • 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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