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A Comprehensive Guide to Green Milkweed (Asclepias viridis)

Green Milkweed (Asclepias viridis) is a herbaceous perennial that is native to the midwestern and southern United States. This plant is a host to the Queen (Danaus gilippus) and Monarch (Danaus plexippus) butterflies. Growing from 0.5 to 2 feet tall, this species has green flowers with purple hoods that bloom from April to October. It is hardy in zones 5-9.

Taxonomy and Naming of Green Milkweed (Asclepias viridis)

Herbarium specimen of green milkweed (Asclepias viridis).
Herbarium Specimen — Asclepias viridis Walter collected in United States of America by The New York Botanical Garden (licensed under CC BY 4.0)
Isoneotype specimen of green milkweed (Asclepias viridis).
Isoneotype Specimen — Asclepias viridis Walter collected in United States of America by The New York Botanical Garden (licensed under CC BY 4.0)

Taxonomy

Green milkweed (Asclepias viridis) was named and described by Thomas Walter, an American botanist, in Flora Caroliniana (1788). 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, viridis, refers to the flower color.

Common Name and Alternative Names

The common name describes the color of the flower. Another common name, green antelope-horn milkweed, describes the purple horns in the flowers. It has been called spider milkweed.

Physical Description

Plant of green milkweed (Asclepias viridis).
Plant of Green Milkweed — Asclepias viridis Walter observed in United States of America by Diana Foreman (licensed under CC0 1.0)
  • Plant Type: This plant is a herbaceous perennial.
  • Height: 0.5 to 2 feet
  • Stem: essentially glabrous
  • Leaves: The leaves are opposite (subopposite), simple, short-petiolate, entire, and ovate to lanceolate in shape. The leaves can be alternate towards the top of the stem (Weakley 2022). The leaves range in size from 1.5 to 5 inches in length and 0.4 to 2 inches in width (Woodson 1954) and Field Guide to Georgia Milkweeds(pdf).
  • Flower color: green (Woodson 1954), yellowish-green (Weakley 2022) or white.
  • Blooming period: This plant blooms from April to October.
  • Fruiting type and period: This plant has follicles that mature in the late summer and fall.

Range of Green Milkweed (Asclepias viridis) in the United States and Canada

Range map of green milkweed (Asclepias viridis) 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-west and southern United States. It is considered to be rare in the states of Georgia, Indiana, and West Virginia.

Habitat

Longleaf pine barren habitat in Florida.
Pine Barren Habitat — National Archives and Records Administration, Public domain, via Wikimedia Commons

This species grows open areas such as glades, prairies, dry hillsides, roadsides (Allison 1995, Lathrop 1958, Whisenant 1981), pasture (Nelson and Harsley 2010), pine barrens, dry woodlands (Dee and Palmer 2017) and calcareous areas (Weakley 2022), including limestone glades (Meehan’s Monthly 1896) and chalk outcrops (Leidolf, et al. 2002).

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) and the Queen Butterfly (Danaus gilippus). This is one of the most abundant milkweed species for monarch butterflies in the southern Great Plains of the United States (Baum and Sharber 2012).

Other Supported Wildlife

Spider milkweed (Asclepias asperula) with honeybee.
Spider Milkweed (Asclepias asperula) — LevyRat, CC0, via Wikimedia Commons

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

Frequently Asked Questions about Green Milkweed (Asclepias viridis)

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.

Does this plant have any ethnobotanical uses?

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

How is this plant distinguished from other milkweeds?

This species is similar to the spider antelope-horn milkweed (Asclepias asperula spp. capricornu), but it differs in that spider antelope-horn milkweed has smaller corolla lobes (7-12 mm vs. 13-17 mm) (Weakley 2022).

Is this plant invasive?

This plant is not considered to be invasive, but has been noted that it can take over places that have been overgrazed (Nelson and Harsley 2010).

Gardening with Green Milkweed (Asclepias viridis)

Add Green Milkweed to Your Garden

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Green flower cluster of green milkweed (Asclepias viridis).
Asclepias viridis Walter observed in United States of America by Alan Prather (licensed under CC BY 4.0)

Hardiness

This species is hardy in zones 5-9. 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 have medium to dry soils that are high in pH. It is best to limit mowing during the early summer to not negatively impact the plants (Dee and Baum 2019). This milkweed is shows higher density in places that have been burned (Baum and Sharber 2012).

Planting Green Milkweed

The seeds of this species, require a period of cold stratification in order to germinate. Because of this it is best to plant the seeds in the fall or early winter. If you get your seeds commercially, make sure that they have been cold stratified.

Additional Tips

This is one of the locally abundant milkweed species in the southern Great Plains and an important food source for migrating monarch butterflies. Make sure that you keep any leaves that appear to have been eaten so the caterpillars have enough plant material to eat.

References

  • Allison, James R. 1995. Prairies…in Georgia! They’re for real, as the flora shows. Tipularia 10: 2-8.
  • Baum, Kristen A. and Wyatt V. Sharber. 2012. Fire creates host plant patches for monarch butterflies. Biology Letters 8: 968-971.
  • Dee, Justin R. and Kristen A. Baum. 2019. Mowing Frequency Influences Number of Flowering Stems but not Population Age Structure of Asclepias viridis, an important Monarch Host Plant. American Midland Naturalist 182 (1): 27-35.
  • Dee, Justin R. and Michael W. Palmer. 2017. Annual rings of perennial forbs and mature oaks show similar effects of climate but inconsistent responses to fire in the North American prairie-forest ecotone. Canadian Journal of Forest Research 47: 716-726.
  • Lathrop, Earl W. 1958. The Flora and Ecology of the Chautauqua Hills in Kansas. The University of Kansas Science Bulletin 39 (4): 97-210.
  • Leidolf, Andreas, Sidney McDaniel, and Tim Nuttle. 2002. The Flora of Oktibbeha County, Mississippi. Sida 20(2): 691-765.
  • Meehan’s Monthly. 1896. Article on Shining Cone-flower Rudbeckia fulgida 221-222.
  • Nelson, A.D. and S. Harsley. 2010. County Records and Major Range Extensions for West Cross Timbers’ Angiosperms from Tarleton State University’s Hunewell Ranch in Erath County, Texas. Texas Journal of Science 62(2): 111-126.
  • Weakley, A.S. and the Southeastern Flora Team. 2022. Flora of the southeastern United States. University of North Carolina Herbarium, North Carolina Botanical Garden.
  • Whisenant, S.G. 1981. The Vascular Flora of McCullough County, Texas. Texas Journal of Science 33 (2,3,4): 197-220.
  • 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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