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A Comprehensive Guide to Hall’s Milkweed (Asclepias hallii)

Hall’s Milkweed (Asclepias hallii) is a herbaceous perennial that is found in the western and southwestern United States. This milkweed is a host plant to the Monarch Butterfly and a nectar plant to others. It can grow up to 3 feet tall and has ovate-lanceolate leaves. The rose to purple flowers bloom from June to August and it is hardy in zones 3-9.

Taxonomy and Naming of Hall’s Milkweed (Asclepias hallii)

Herbarium specimen of halls milkweed (Asclepias hallii).
Herbarium Specimen — Asclepias hallii A.Gray collected in United States of America by The New York Botanical Garden (licensed under CC BY 4.0)
Isotype specimen of halls milkweed (Asclepias hallii).
Istoype Specimen — “Asclepias hallii (YU.065673). Digital Image: Yale Peabody Museum of Natural History; photo by Division of Botany, Yale Peabody Museum 2012″ – Asclepias hallii A.Gray collected in United States of America (licensed under CC0 1.0)

Taxonomy

Hall’s Milkweed (Asclepias hallii) was named and described by Asa Gray, an American botanist, in the Proceedings of the American Academy of Science in 1877. While the original specimen of the description is unknown, the neotype is a specimen collected in 1939 from near Georgetown, South Carolina. This species has kept the same name since. This plant 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 genus name, hallii, is a Latinized form of the person for whom the plant is named, presumably Harry Hall (Wikipedia).

Common Name

The common name of this plant refers presumably to Harry Hall as above. Other names for the plant, such as purple silkweed, are in reference to the color of the fruits.

Physical Description of Hall’s Milkweed (Asclepias hallii)

Red and white flowers of halls milkweed (Asclepias hallii).
Frankie Coburn, CC-BY-SA

Description

  • Plant Type: Herbaceous perennial
  • Height: 1 to 3 feet
  • Leaves: alternate to opposite, simple, entire, ovate to lanceolate leaves that are 2-6 inches in length and 1-2 inches in width. The leaves are described as being thick (gardenology).
  • Stem: Green to purple that are puberulent to glabrate
  • Flower color: white, whitish green, rose, pink to purple
  • Blooming period: June to August
  • Fruiting type and period: follicle that matures in the fall

Range of Hall’s Milkweed (Asclepias hallii) in the United States and Canada

Range map of hall's milkweed (Asclepias hallii) in the United States and Canada.
Kartesz, J.T., The Biota of North America Program (BONAP). 2015. North American Plant Atlas. (https://bonap.net/napa). Chapel Hill, N.C. [maps generated from Kartesz, J.T. 2015. Floristic Synthesis of North America, Version 1.0. Biota of North America Program (BONAP). (in press)].

This species is native to the west and southwestern United States. This plant is considered to be rare in most of the states where it occurs including Wyoming, Utah, Colorado, and New Mexico.

Habitat

Steppe habitat for halls milkweed.
Steppe Habitat — Patrick Alexander from Las Cruces, NM, CC0 1.0, via Wikimedia Commons

This milkweed is found growing on prairies, roadsides, rocky slopes, steppes, and woodlands that are between about 6,000 to 8,000 feet in elevation. Soils are generally sandy and well-drained.

Hosted Insects

Purple coneflower (Echinacea purpurea) with Monarch butterfly.
Monarch Butterfly on Purple Coneflower — Robert Coxe, Image

This milkweed, like a lot of milkweeds, is a host to the Monarch Butterfly (Danaus plexippus). It is also a host to the Queen Butterfly (Danaus gilippus).

Other Supported Wildlife

Spider milkweed (Asclepias asperula) with honeybee.
Honeybee on Milkweed — LevyRat, CC0 1.0, via Wikimedia Commons

This milkweed, again like a lot of other milkweeds, is a nectar source to other insect species, including bees and other butterflies such as the Nevada Skipper (Hesperia nevada) (Encyclopedia of Life).

Frequently Asked Questions about Hall’s Milkweed (Asclepias hallii)

Is this species poisonous?

This plant, as are all milkweeds, is considered to be poisonous because of the presence of cardiac cardenolides/glycosides in the milky sap.

What other species are similar to this plant?

According to the Colorado Natural Heritage Program this plant is not often confused with any other milkweed (Colorado Rare Plant Guide). However, it has been described as being similar to Asclepias jorgeana, but differs in that it has alternate leaves and the Asclepias jorgeana is found in Mexico (Fishbein and Lynch 1999).

Does this plant have any Native American uses?

This species has been used for a gynecological aid and veterinary aid (North American Ethnobotany Database).

Gardening with Hall’s Milkweed (Asclepias hallii)

Add Hall’s Milkweed to Your Garden

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Pinkish flowers of halls milkweed (Asclepias hallii).
Halls Milkweed — Asclepias hallii A.Gray observed in United States of America by Ashwin Srinivasan (licensed under CC BY 4.0)

Hardiness

This species is hardy in zones 3-9. If your garden is within these zones and you have the right soil and moisture conditions, you can likely grow it even if you are not in the native range. The hosted insects for this species, the monarch butterfly (Danaus plexippus) and the Queen butterfly (Danaus gilippus) are wide ranging and are likely to be in your area. However, they may not be if you are out of the native range.

Optimal Conditions

This milkweed prefers places that have full sun, but can handle partial shade. Soils should be sandy and well-drained.

References

  • Fishbein, Mark and S.P. Lynch. 1999. Asclepias jorgenana (Asclepiadaceae), a new milkweed from montane western Mexico. Novon 9: 179-184.
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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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