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A Comprehensive Guide to Aquatic Milkweed (Asclepias perennis)

Aquatic Milkweed (Asclepias perennis) is a herbaceous perennial that is native to the south-central and southeastern United States. This plant is a host to the Queen (Danaus gilippus) and Monarch (Danaus plexippus) butterflies. Growing from 1 to 3.5 feet tall, this species has white to pink flowers that bloom from April to October. It is hardy in zones 6-10.

Taxonomy and Naming of Aquatic Milkweed (Asclepias perennis)

Herbarium specimen of aquatic milkweed (Asclepias perennis).
Herbarium Specimen — Asclepias perennis Walter collected in United States of America by The New York Botanical Garden (licensed under CC BY 4.0)
Type specimen of aquatic milkweed (Asclepias perennis).
Aquatic Milkweed Type Specimen — Harvard University Public Domain Type Specimen

Taxonomy

Aquatic Milkweed (Asclepias perennis) was originally named and described by Thomas Walter, an American botanist, in 1788, based on a specimen in the state of South Carolina. This species has been a succession of other names through time but currently has the original name as given by Walter. This species 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, perennis, is Latin for perennial or everlasting.

Common Name and Alternative Names

The common name comes from the habitat where this plant is found. Some other common name found include swamp milkweed (Mohlenbrock and Voigt 1965), likely in reference to a common habitat, thin-leaved milkweed (Yatskievych 1995), perennial milkweed (Featherman 1871) and small-flowered milkweed (Mohr 1901).

Physical Description of Aquatic Milkweed (Asclepias perennis)

Plant of aquatic milkweed (Asclepias perennis) with white flowers in a wetland.
Plant of Aquatic Milkweed — Asclepias perennis Walter observed in United States of America by Jody Shugart (licensed under CC BY 4.0)

Description

  • Plant Type: This plant is a herbaceous perennial
  • Height: 1 to 3.5 feet
  • Stem: The stem is ascending, simple, and slightly pubescent (Woodson 1954). In Illinois it was noted to have a bright green stem (Benke 1929), while generally it is greenish-purple. The lower part of the stem can be woody (Mohr 1901).
  • Leaves: The leaves are opposite, simple, and oblong to ovate-elliptic in shape. The leaves are 2 to 6 inches long and about 0.2 to 0.6 inches wide. They have been described as thin (Britton 1913) and membranaceous (Correll and Correll 1972).
  • Flower color: white to pink or white with pinkish hues, purplish-rose or purple
  • Blooming period: This plant blooms from April to October, depending on location.
  • Fruiting type and period: This plant has follicles that mature in the late summer and fall.

Range of Aquatic Milkweed (Asclepias perennis) in the United States and Canada

Range of aquatic milkweed (Asclepias perennis) 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 south-central, mid-west, and southeastern United States. This species has also been noted to be in Guatemala (GBIF) and Cuba (Sauvelle and Grisebach 1873).

Habitat

Swamp Habitat in Europe.
Swampland Habitat — Ina Hensel (telemakro.de), CC BY-SA 4.0, via Wikimedia Commons

This species grows in places that are wet or moist such as the margins of swamps, alluvial woods, ditches, and marshes.

Hosted Insects

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

Frequently Asked Questions about Aquatic Milkweed (Asclepias perennis)

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 shows that this plant has been used for a number of pharmaceutical uses and for fishing.

How is this plant distinguished from other milkweeds?

This species is similar to the bract milkweed (Asclepias brachystephana), but bract milkweed has thicker leaves and is short-petioled. Aquatic milkweed is also close to four-leaf milkweed (Asclepias quadrifolia), but the four-leaf milkweed has 3-5 pairs of leaves, versus the 6+ pairs that aquatic milkweed has (Deam 1940).

Is this plant invasive?

This plant has been noted as becoming weedy in cultivated fields (Correll and Correll 1972).

Gardening with Aquatic Milkweed (Asclepias perennis)

Aquatic milkweed (Asclepias perennis) with white flowers in floodplain forest.
Plant of Aquatic Milkweed in a Floodplain Forest — Asclepias perennis Walter observed in United States of America by Étienne Lacroix-Carignan (licensed under CC0 1.0)

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 where there is a lot of moisture and gets full to partial sun.

Additional Notes about this Plant

This species of milkweed has been compared with butterfly weed as being one of the best garden milkweeds (Pelton 1996).

References

  • Benke, H.C. 1929. Notes on the fall-flowering plants of the central Mississippi River valley. Rhodora 31: 145-151.
  • Britton, Nathaniel Lord. 1913. An Illustrated Flora of the northern United States, Canada, and the British possessions: from Newfoundland to the parallel of the southern boundary of Virginia, and from the Atlantic Ocean westward to the 102nd meridian. (New York: C. Scribner’s Sons v. 3.
  • Correll, Donovan Stewart and Helen B. Correll. 1972. Aquatic and wetland plants of southwestern United States (Washington, DC: EPA).
  • Deam, Charles Clemon. 1940. Flora of Indiana. (Indianapolis: Indiana Department of Conservation).
  • Featherman, A. 1871. Report of botanical survey of southern and central Louisiana made during the year 1870. (New Orleans: Office of the Republican).
  • Mohlenbrock, Robert H. and John W. Voigt. 1965. An Annotated Checklist of Vascular Plants of the Southern Illinois University Pine Hills Field Station and Environs. Transactions of the Illinois State Academy of Science 58: 268-301.
  • Mohr, Charles E. 1901. Plant Life of Alabama. Contributions from the United States National Herbarium v. 6.
  • Pelton, John. 1996. An April 1996 Field Trip in the Ouachitas. Claytonia Fall 1996.
  • Sauvelle, Francisco Adolfo and A. Grisebach. 1873. Flora cubana, Enumeratio nova plantarum cubesinum. (Havanna: La Antilla de Cacho-Negrete.
  • Woodson, Robert E. 1954. The North American Species of Asclepias L. Annals of the Missouri Botanical Garden 41: 1-211.
  • Yatskievych, Kay. 1995. The Milkweed Family in Indiana. Indiana Native Plant and Wildflower Society News 2(2): 1.
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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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