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A Comprehensive Guide to Utah Milkweed (Asclepias labriformis)

Utah Milkweed (Asclepias labriformis) is a herbaceous perennial that is native to the state of Utah in the United States. This plant is a host to the Queen (Danaus gilippus) and Monarch (Danaus plexippus) butterflies. Growing from 8 inches to 20 inches tall, this species grows in washes, sandstone canyons, and dry cliffs. The yellowish-green flowers bloom from May to August and the plant is hardy in zone 5.

Taxonomy and Naming of Utah Milkweed (Asclepias labriformis)

Herbarium specimen of Utah milkweed (Asclepias labriformis).
Herbarium specimen — Asclepias labriformis M.E.Jones collected in United States of America by The New York Botanical Garden (licensed under CC BY 4.0)

Taxonomy

Utah Milkweed (Asclepias labriformis) was originally named and described by Marcus Jones, an American botanist in 1895. This species 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, labriformis, might come from the presence of labriformidin, a toxic substance in the plant (Wordsense.eu).

Common Name and Alternative Names

The common name is derived from the growing location of the plant. Other common names include poison milkweed and labriform milkweed.

Physical Description

Yellowish-green flowers of Utah milkweed (Asclepias labriformis) in a sandy area.
Flowers of Utah Milkweed — “2020.05.09_11.24.38_IMG_5911” by AndreyZharkikh is licensed under CC BY 2.0.
  • Plant Type: This plant is a herbaceous perennial.
  • Height: 8 inches to 20 inches tall
  • Stem: The stem is thin and erect and sometimes branches. It may puberulent when young but become glabrous with age (Woodson 1954).
  • Leaves: The leaves are approximate, subsessile, lanceolate to linear-lanceolate and are 2 to 6 (7) inches long and 0.2 to 1 inches wide. The leaves are thick and leathery (Jones 1895) and glabrous (Welsh, et al 1987).
  • Flower color: yellowish-green (Woodson 1954) to greenish-white (Jones 1895)
  • Blooming period: This plant blooms from May to August.
  • Fruiting type and period: This plant has follicles that mature in the late summer and fall.

Range of Utah Milkweed in the United States and Canada

Range map of Utah milkweed (Asclepias labriformis) 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 Utah in the United States.

Habitat

Dry rocky woodland habitat.
Dry Rocky Woodland — Patrick Alexander from Las Cruces, NM, CC0, via Wikimedia Commons

This species grows in washes and canyons (Woodson 1954), desert shrub (Harris 1983), the sand of old stream beds (Brotherson, et al 1980), roadsides (Heil 2013), and Pinyon-Juniper woodlands (Welsh, et al 1987).

Hosted Insects

Monarch butterfly (Danaus plexippus) on goldenrod.
Monarch Butterfly on Goldenrod — ALAN SCHMIERER from southeast AZ, USA, CC0, via Wikimedia Commons

Other Supported Wildlife

Bumblebee on pink flower.
Bumblebee on Flower — Weerlicht, CC0, via Wikimedia Commons

This species is a nectar source to other butterflies, skippers, bees, and wasps during the growing season.

Frequently Asked Questions

Is this plant poisonous?

Like other milkweeds, it has cardiac glycosides (cardenolides) and is considered to be poisonous with ingestion. This has been noted as being poisonous to cattle (Graham 1937) and to sheep (Brotherson, et al 1980). This plant has been considered among the most toxic of the milkweeds (gardenia.net).

Does this plant have any ethnobotanical uses?

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

How is this plant distinguished from other milkweeds?

This species is most similar to the Humboldt Mountain Milkweed (Asclepias cryptoceras). However, Humboldt Mountain Milkweed has ovate leaves and Utah Milkweed has lanceolate to linear-lanceolate leaves (Tidestrom 1925).

Is this plant invasive?

This plant has not been noted as being weedy and is endemic to the state of Utah.

Gardening with Utah Milkweed

Plant of Utah milkweed (Asclepias labriformis) in a sandy area.
Plant of Utah Milkweed in a Sandy Area — “2020.05.09_11.24.20_IMG_5910” by AndreyZharkikh is licensed under CC BY 2.0.

Hardiness

This species is hardy in zone 5. 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 can grow in full sun to partial-shade in well-drained soil to that is dry to wet.

References

  • Brotherson, Jack D., LA Szyska, and William E. Evenson. 1980. Poisonous Plants of Utah USA. The Great Basin Naturalist 40: 229-250.
  • Graham, Edward H. 1937. Botanical Studies in the Uinta Basin of Utah and Colorado. Annals of the Carnegie Museum 26: 1 -432.
  • Harris, James G. 1983. A Vascular Flora of the San Rafael Swell, Utah. The Great Basin Nautralist 43: 79-87.
  • Heil, Kenneth D., Steve L/ O’Kane, Linda Mary Reeves, and Arnold Clifford. 2013. Flora of the four corners region: vascular plants of the San Juan River drainage, Arizona, Colorado, New Mexico, and Utah. Monographs in systematic botany from the Missouri Botanical Garden v. 124.
  • Jones, Marcus E. 1895. Contributions to Western Botany. No. VII. Proceedings of the California Academy of Science 2(5): 708.
  • Tidestrom, Ivan. 1925. Flora of Utah and Nevada. Contributions from the United States National Herbarium 25.
  • Welsh, Stanley L., Duane N. Atwood, and Sherel Goodrich. 1987. A Utah Flora. Great Basin Naturalist Memoirs 9: 1-895.
  • Woodson, Robert. 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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