Skip to content

A Comprehensive Guide to Narrow-leaf Milkweed (Asclepias fascicularis)

Narrow-leaf Milkweed (Asclepias fascicularis) is a herbaceous perennial that is found in the western United States. This plant is a host to three butterflies, including the Monarch butterfly (Danaus plexippus). Growing from 1 to 3.5 feet tall, this species has flowers that range from grayish-pink, white to lavender that bloom from May to October. It is hardy in zones 6-10.

Taxonomy and Naming of Narrow-leaf Milkweed (Asclepias fascicularis)

Herbarium specimen of narrow-leaf milkweed (Asclepias fascicularis).
Herbarium Specimen — Asclepias fascicularis Decne. collected in United States of America by The New York Botanical Garden (licensed under CC BY 4.0)

Taxonomy

Narrow-leaf milkweed (Asclepias fascicularis) was named and described by Joseph Decaisne, a French botanist, in 1844. The species has kept this name since 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, fascicularis, is Latin for bundles referring to the leaves (Calflora.net).

Common Name and Alternative Names

The common name describes the narrowness of the leaves. Other common names are variations of the common name with or without hyphens. Some other common names describes the location of the plant such as Mexican milkweed, Mexican whorled milkweed, California milkweed.

Physical Description of Narrow-leaf Milkweed (Asclepias fascicularis)

Pinkish flowers of narrow-leaf milkweed (Asclepias fascicularis).
Flowers of Narrow-leaf Milkweed — Thayne Tuason, CC BY-SA 4.0, via Wikimedia Commons

Description

  • Plant Type: This plant is a herbaceous perennial.
  • Height: 1 to 3.5 feet
  • Stem: pubescent to glabrous
  • Leaves: The leaves are opposite, simple (3-nate to 4-nate), entire, and oblong to linear-lanceolate in shape. The leaves range in size from 1.25 to 5 inches in length and 0.1 to 1 inches in width (Woodson 1954).
  • Flower color: Grayish-pink to white (Woodson 1954), lavender to lavender-white (calscape.org), white and peach (Ljubenkov and Ross 2002) or greenish-white (Jepson eflora).
  • Blooming period: This plant blooms from May to October.
  • Fruiting type and period: This plant has follicles that mature in the late summer and fall.

Range of Narrow-leaf Milkweed (Asclepias fascicularis) in the United States and Canada

Range map of narrow-leaf milkweed (Asclepias fascicularis) 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 found in the western United States. It is not considered to be rare in any part of its range. This species is also found in northern Mexico on the Baja peninsula.

Habitat

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

This species is generally in places of dry substrate that are open such as grasslands, pastures, roadsides, disturbed areas (landfills) and woodlands in valleys, plains, and slopes. It is occasionally found in wetlands such as vernal pools (Pipevine 2016) and riparian floodplains (Fraga 2006 and Fraga et al. 2011) and in sandy soil (Roberts and Bramlet 2007).

Hosted Insects

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

This species is a host for the Monarch Butterfly (Danaus plexippus) and the Queen Butterfly (Danaus gilippus). This milkweed is present further into the season and therefore provides food for late butterflies (Fadem and Shapiro 1979). Another study found that while monarchs do not have a strong preference for this plant (Ladner and Altizer 2005 and Robertson, et al 2015), their survival and growth is better on this plant (Ladner and Altizer 2005).

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 have been noted to use the stems for nesting (San Luis Obispo Botanical Garden). Bees are fond of this plant and it has been recognized as a honey source (Krochmal 2016).

Frequently Asked Questions about Narrow-leaf Milkweed (Asclepias fascicularis)

Is this plant poisonous?

Like other milkweeds, it has cardiac glycosides (cardenolides) and is considered to be poisonous with ingestion. Because of the poisonous nature of the plant it is deer resistant. This milkweed has been described as one of the most toxic (gardenia.net).

Does this plant have any ethnobotanical uses?

The Native American Ethobotanical Database notes that this species has been used as a snakebite remedy, foods, and fibers. Gum for adhesives has been made from this plant by the Coahuilla Indians (Barrows 1900).

How is this plant distinguished from other milkweeds?

This species is very similar to the swamp milkweed (Asclepias incarnata), but the ranges are different. Swamp milkweed is found in the eastern United States, while this species is confined to the western United States. Woodson 1954, calls this plant the western Asclepias incarnata because of the similarity. Narrow-leaf milkweed is also similar to horsetail milkweed (Asclepias subverticillata), but the leaves of the latter are much more linear and it generally has one flower in the upper nodes (Woodson 1954).

Is this plant invasive?

Calscape notes that this species can become weedy. It has been noted as being weedy in Idaho (Sage Notes 2012).

Gardening with Narrow-leaf Milkweed (Asclepias fascicularis)

Add Narrow-leaf Milkweed to Your Garden

The link below takes you to our product page where we get a small commission from your purchase at no additional cost to you.

Plant of narrow-leaf milkweed (Asclepias fascicularis).
Narrow-leaf Milkweed (Asclepias fascicularis) — glmory, CC0, via Wikimedia Commons

Hardiness

This species is hardy in zones 6-10. 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 it can receive full sun and can tolerate clayey and poor soils that are well-drained.

Additional Notes

Narrow-leaf milkweed is the most used milkweed in revegetation projects in California (Honig 2013) and is noted for attracting beneficial insects (James, et al. 2016).

References

  • Barrows, David Prescott. 1900. The ethno-botany of the Coahuilla Indians of Southern California. Chicago: University of Chicago Press.
  • Fadem, Cheryl M. and Arthur M. Shapiro. 1979. Notes on Winter Roosting by Monarchs (Lepidoptera: Danaidae) at an Inland Site in California. Pan-Pacific Entomologist 55: 309-310.
  • Fraga, Noami S., et al. 2011. The Vascular Flora of the Upper Santa Ana River Watershed, San Bernardino Mountains, California. Crossosoma 37(1): 1-111.
  • Fraga, Noami S. 2006. A Short Flora of Short Canyon, Kern County, California. Crossosoma 32(1): 1-32.
  • Honig, Sasha. 2013. Gardening with Native Plants – Plant milkweed and help a butterfly. Mimulus Memo California Native Plant Society – Kern Chapter. Page 4.
  • James, David G., et al. 2016. Beneficial Insect Attraction to Milkweeds (Asclepias speciosa, Asclepias fascicularis) in Washington State, USA. Insects 7(3): 30.
  • Krochmal, Connie. 2016. Milkweeds as Honey Plants. Bee Culture 144 (9): 35-40.
  • Ljubenkov, Julie A. and Timothy S. Ross. 2002. An Annotated Checklist of the Vascular Plants of the Whittier Hills, Los Angeles County, California. Crossosoma 27(1): 1-23.
  • Ladner, Deborah T. and Sonia Altizer. 2005. Oviposition preference and larval perfomance of North American monarch butterflies on four Asclepias species. Entomologia Experimentalis et Applicata 116 (1): 9-20.
  • Roberts, Fred M. and David E. Bramlet. 2007. Vascular Plants of the Donna O’Neill Land Conservancy, Rancho Mission Viejo, Orange County, California. Crossosoma 33(1): 2-38.
  • Robertson, G., M. Zalucki, and T. Paine. 2015. Larval Host Choice of the Monarch Butterfly (Danaus plexippus L.) on Four Native California Desert Milkweed Species. Journal of Insect Behavior 28 (5): 582-592.
  • Sage Notes. 2012. Six Asclepias Native to Idaho. Sage Notes 34(2): 5.
  • The Pipevine. 2016. Rare Plants in Dry Vernal Pools Vina Plains Preserve. California Native Plant Society. Chico, CA.
  • Woodson, Robert E. 1954. The North American Species of Asclepias L. Annals of the Missouri Botanical Garden 41: 1-211.
Share this post on social!

Leave a Reply

Your email address will not be published. Required fields are marked *

6 + 17 =

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.

The owner of this website has made a commitment to accessibility and inclusion, please report any problems that you encounter using the contact form on this website. This site uses the WP ADA Compliance Check plugin to enhance accessibility.