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Clasping Milkweed (Asclepias amplexicaulis), a Comprehensive Guide in 10 Sections

Introduction

Clasping Milkweed (Asclepias amplexicaulis) is a herbaceous perennial that is native to the eastern half of the United States except for Maine. 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 clasping leaves. The greenish-pink, red, brown to purple flowers bloom from March to September, depending on location. More about Clasping Milkweed can be found on this post.

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Taxonomy and Naming of Clasping Milkweed (Asclepias amplexicaulis)

Herbarium specimen of Clasping Milkweed (Asclepias amplexicaulis).
Clasping Milkweed —  Asclepias amplexicaulis Sm. collected in United States of America by The New York Botanical Garden (licensed under CC BY 4.0)

Taxonomy

Clasping Milkweed (Asclepias amplexicaulis) was named and described by James Edward Smith, an English botanist, in 1797 in Flora et Entomologia: The Natural History of the Rarer Lepidopterous Insects of Georgia (Smith and Abbot 1797). The specimen was presumably from the state of Georgia (Britten 1898). It 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 species name, amplexicaulis, in Latin means “embracing the stem” (Save the Dunes).

Common Name and Alternative Names

The common name refers to the leaves clasping the stem. Some alternative names, such as blunt-leaved milkweed and curly milkweed, are also descriptive of the leaves. Another, sand milkweed, describes the habitat of the species, while red milkweed, is descriptive of the flower color.

Physical Description of Clasping Milkweed (Asclepias amplexicaulis)

Clasping Milkweed (Asclepias amplexicaulis) in a wooded setting.
Clasping Milkweed in a wooded setting — cassi saari, CC BY-SA 4.0, via Wikimedia Commons

Description

  • Plant Type: Herbaceous perennial
  • Height: about 1 to 3 feet tall
  • Leaves: opposite, simple, ovate to oblong-lanceolate, crenate to entire leaves that are 3-6 inches in length and 1-3 inches in width. The leaves are sessile to the stem and have a white to pink midrib. The margins are generally undulate (wavy) and the leaves have a waxy appearance with a mucronate tip.
  • Stem: green to pinkish. Stems exude a milky sap when cut.
  • Flower color: red, blue, green, brown to pink. Rarely the flowers can be maroon-purple (Uttal 1955).
  • Blooming period: March to September
  • Fruiting type and period: Brown to cream color follicle that comes out in June to September

The flowers have a rose or clove scent (NC Extension Gardener). This plant can sometimes hybridize with the pinewoods milkweed (Asclepias humistrata) (Woodson 1954).

Range Map of Clasping Milkweed (Asclepias amplexicaulis) in the United States and Canada

Range map of Clasping Milkweed (Asclepias amplexicaulis) in the United States and Canada.

This species is native to the midwest and eastern half of the United States except for Maine. It is considered to be rare in New Hampshire, Vermont, Ohio, Minnesota, and Nebraska.

Habitat

Sandy woodland habitat in Delaware.
Sandy woodland habitat in Delaware — author image

This species grows in dry woodlands, prairies, meadows, and roadsides with sandy or gravelly soil. In Minnesota, where it is considered a threatened species, it is found only on “sparsely vegetated savanna” (Minnesota Wildflowers).

Hosted Insects

Monarch butterfly (Danaus plexippus) on a green flower.
Monarch Butterfly on a green flower — U.S. Fish and Wildlife Service, Public domain, via Wikimedia

This species is a host to the Monarch Butterfly (Danaus plexippus) and likely also the Queen Butterfly (Danaus gilippus), the milkweed stem weevil (Rhyssomatus lineaticollis), and sweat bees (Coastal Plain Plants).

Other Supported Wildlife

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

This milkweed, like a lot of other milkweeds, is a nectar source to other species such as bees.

Frequently Asked Questions about Clasping Milkweed (Asclepias amplexicaulis)

Is it considered to be toxic to pets?

This milkweed, like other milkweeds, contains cardiac cardenolides in the milky sap, which are toxic to animals and humans.

Is it invasive?

It is not likely invasive, since it requires a specific habitat where there no much competition from other plants. There is no mention in the literature of any invasive characteristics. The Global Biodiversity Information Facility shows that the only place where it has been introduced beyond its native range are the islands of Saint Helena and Tristan da Cunha.

Is Clasping Milkweed a good addition to your butterfly garden?

If you are looking for diversity in milkweeds and have the right conditions as far as light, soil, and hardiness zone, it would be. However, as far as insect visitors it is likely not the best plant of the milkweeds. A study on the insect herbivores of milkweed species, showed that this species was one of the least utilized of the milkweeds (Betz, et al 1999).

What other milkweeds are similar to this species?

Green milkweed (Asclepias viridiflora) looks a lot this species, but the green milkweed does not have the clasping and sessile leaves (Minnesota Wildflowers).

Gardening with Clasping Milkweed (Asclepias amplexicaulis)

Rose-pink flowers of Clasping Milkweed (Asclepias amplexicaulis) in a field.
Rose-pink flowers of Clasping milkweed — “Asclepias amplexicaulis – Clasping Milkweed” by FritzFlohrReynolds is licensed under CC BY-SA 2.0.

Hardiness

This species is hardy in zones 3-9. If your garden is within these zones, you can likely grow it even if you are not in the native range and have the right soil and moisture conditions. Be aware that this plant is particular about its environment and does not like competition. The hosted species, the monarch butterfly (Danaus plexippus) is present in most areas of the United States, although this plant is not one the favored milkweeds.

Optimal Conditions

This milkweed requires places with full sun to partial shade that moist to dry sandy soil.

References

  • Betz, Robert F., William R. Rommel, and Joseph J. Dichtl. 1999. Insect herbivores of 12 milkweed (Asclepias) species. Proceedings of the Fifteenth North American Prairie Conference.
  • Britten, James. 1898. Smith’s Georgian Plants. Journal of Botany, British and Foreign. 36: 297-302.
  • Smith, J.E. Smith and J. Abbot. 1797. Flora et Entomologia: The Natural History of the Rarer Lepidopterous Insects of Georgia.
  • Uttal, Leonard J. 1955. A dark-hooded variant of Asclepias amplexicaulis. Rhodora 57: 336-337.
  • Woodson, R.E. 1954. The North American Species of Asclepias L. Annuals of the Missouri Botanical Garden 41: 1-211.
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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 for Silphium Design LLC.

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