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A Comprehensive Guide to Pineneedle Milkweed (Asclepias linaria)

Pineneedle Milkweed (Asclepias linaria) is a herbaceous perennial that is native to the states of Arizona and New Mexico in the United States and ranges south into Mexico. This plant is a host to the Queen (Danaus gilippus) and Monarch (Danaus plexippus) butterflies. Growing from 1.5 to 6 feet tall, this species grows in open woodlands, limestone ridges, and waste places. The greenish-white flowers bloom from April to October and the plant is hardy in zones 9-11.

Taxonomy and Naming of Pineneedle Milkweed (Asclepias linaria)

Herbarium specimen of pine-needle milkweed (Asclepias linaria).
Herbarium Specimen — Asclepias linaria Cav. collected in United States of America by The New York Botanical Garden (licensed under CC BY 4.0)

Taxonomy

Pineneedle Milkweed (Asclepias linaria) was originally named and described by Antonio Jose’ Cavanilles, a Spanish botanist in 1791. It has kept this same 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, linaria, is Latin for needle.

Common Name and Alternative Names

The common name refers to the needle-like appearance of the leaves. Some other common names include narrow-leaf milkweed (Felger, et al 2012) and threadleaf milkweed (davesgarden.com). In Mexico, this plant is known as Venenillo (Watson 1883). This species is planted on the island of Bermuda and is called Ranstead Milkweed there (Britton 1918).

Physical Description

Close-up of flowers of pineneedle milkweed (Asclepias linaria).
White Flowers of Pineneedle Milkweed — Asclepias linaria Cav. Observed in Mexico by Juan Carlos Fonseca Mata (licensed under CC BY 4.0)
  • Plant Type: This plant is suffruticose or shrubby.
  • Height: 1.5 to 6 feet tall
  • Stem: The stem is woody and pilose when young but glabrous in age (Woodson 1954).
  • Leaves: The leaves are approximate, sessile, filiform and are 0.5 to 2 inches long and 0.04 inches wide.
  • Flower color: greenish-white (Woodson 1954) to white (Gentry 1942).
  • Blooming period: This plant blooms from April to November.
  • Fruiting type and period: This plant has follicles that mature in the late summer and fall.

Range of Pineneedle Milkweed in the United States and Canada

Range map of pine-needle milkweed (Asclepias linaria) 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 states of Arizona and New Mexico in the United States. Its range extends south into Mexico and Central America.

Habitat

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

This species grows in open woodlands, rocky hills, sandy slopes (Woodson 1954), open ground (Meagher 1995), fields (Laferriere 1994), and limestone areas (Smith 1965).

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. A wasp (Eucerceris montana) has been noted to nectar on this species in Mexico (Scullen 1968). One study (McVaugh 1952) noted that this plant was particularly attractive to bees and wasps.

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 cite this species specifically, but milkweeds in general have been used for pharmaceuticals, fibers, and foods. In Mexico, this species has been used for post-partum baths, for cramps (Canales-Martinez, et al 2006), and for headaches (Standley 1920).

How is this plant distinguished from other milkweeds?

This species is most similar to long-hood milkweed (Asclepias macrotis), but differs in that long-hood milkweed has opposite leaves and pineneedle milkweed has alternate leaves (Kearney and Peebles 1942). In Mexico, this species is similar to Asclepias conzattii, but A. conzattii has much bigger leaves at 3 to 5 inches (Veronica 2003).

Is this plant invasive?

This plant has not been noted as being weedy and is restricted to the states of Arizona and New Mexico in the United States.

Gardening with Pineneedle Milkweed

Add Pineneedle Milkweed to Your Garden

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White flower cluster of pineneedle milkweed (Asclepias linaria).
Flowers of Pineneedle Milkweed — Asclepias linaria Cav. Observed in Mexico by cornsnek (licensed under CC BY 4.0)

Hardiness

This species is hardy in zone 9-11. 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.

References

  • Britton, Nathaniel Lord. 1918. Flora of Bermuda. (New York: Scribner and Sons).
  • Canales-Martinez, Maria Margarita, Tzasna’ Hernandez Delgado, Nieto Cabellero. 2006. Analisis cuantitativo del conocimiento tradicional de las plantas medicinales en San Rafael, Coxcatlan, Valle de Tehuacan-Cuicatlan, Puebla, Mexico. Acta Botanica Mexicana 75: 21-43.
  • Felger, Richard Stephen, Susan Rutman, Thomas R. Van Devender, and Steven M. Buckley. 2012. Checklist of the Vascular Plants of Organ Pipe Cactus National Monument, Cabeza Preita National Wildlife Refuge, and Tinjas Altas, Arizona. Canotia 8(1): 1-53.
  • Gentry, Howard Scott. 1942. Rio Mayo Plants, A Study of the Flora and Vegetation of The Valley of the Rio Mayo, Sonora. Carnegie Institution of Washington Publication 527.
  • Kearney, Thomas H. and Robert H. Peebles. 1942. The Flowering Plants and Ferns of Arizona. USDA Miscellaneous Publication 423.
  • Laferriere, Joseph A. 1994. Vegetation and flora of the Mountain Pima village of Nabogame, Chihuahua, Mexico. Phytologia 77: 102-140.
  • McVaugh, Rogers. 1952. A Trip to Botanically Little-Known Area in Queretaro. The Asa Gray Bulletin 1: 169-174.
  • Meagher, Walter L. 1995. Flora of El Jardin Botanico, El Charco Del Igenio San Miguel De Allende, Guanojuanto, Mexico. Phytologia 78: 317-352.
  • Scullen, Herman A. 1968. A Revision of the Genus Eucerceris Cresson (Hymenoptera: Sphecidae). United States National Museum Bulletin.
  • Smith, C. Earle. 1965. Flora Tehuacan Valley. Fieldiana Botany v. 31 publication 987.
  • Standley, Paul Carpenter. 1920. Trees and Shrubs of Mexico. Contributions from United States National Herbarium v. 23.
  • Veronica, Juarez-Jaimes and Lucio Lozada. 2003. Flora del Valle De Tehuacan-Cuicatlan. Unversidad Nacional Autonoma de Mexico fasc. 37.
  • Watson, Sereno. 1883. Contributions to American Botany. Proceedings of the American Academy of Science 18: 96-196.
  • 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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