Asclepias incarnata L.

Leslie Cagle
Ecology Major
University of Georgia
Athens
lcagle@arches.uga.edu OR cagle.leslie@epa.gov

Photographed by W. H. Duncan on March 7, 1975 in Accomack County, Va.  Courtesy of The University of Georgia Herbarium.  Copyright Department of Botany, UGA, Athens. 
 

COMMON NAME:
    Milkweed; Swamp Milkweed
 

HIGHER TAXA:


IDENTIFICATION:
    The A. incarnata is a perennial that is four to five feet in height with pink to pinkish purple hourglass shaped flowers.  The flowers are about 1/3 inch long and grow in clusters upon the smooth, branched stems.  Each flower has five greenish sepals turned downward, five petals, five stamens associated with the central column, and pistols with two ovaries.  The A. incarnata has  leaves that are mid green and grow up to four inches long and up to one inch wide.  They are narrow with a rounded base and a pointed tip (lance shaped).  The swamp milkweed is the only wetland milkweed with milky sap, opposite, lanceolate leaves, and flowers of this color, as opposed to shades of orange.  The flowers are followed by an erect fruit up to three inches long.  These fruits are pods containing numerous seeds with silky hairs.  Click here to link to a site with another picture of a blooming swamp milkweed.  Click here to link to a site with a picture of a fruiting one.  Linnaeus is the authority who described this species in 1753.  The scientific reference where this is discribed is the Index Hortensis and a scientific reference that includes the species with an identification key is the Popular Encyclopedia of Plants.  A paratype is located at the UGA herbarium in Athens, Ga.

GEOGRAPHY:
 
                   AREA 
   STATUS               REFERENCES 
North America:
Continental United States; Canada
        Yes Northern Prairie Wildlife Research Center
Eastern North America:
United States east of the Mississippi;
Ontario and eastern Canada
        Yes Northern Prairie Wildlife Research Center
Southeastern United States:
AL AR DE DC FL GA KY SC TN VA WV
Yes, with the
exception of 
         FL
Northern Prairie Wildlife Research Center
Southern Appalachian States:
AL GA KY MD NC SC TN VA WV
        Yes Northern Prairie Wildlife Research Center
Coastal Plain Widespread
excluding 
southeast GA
Northern Prairie Wildlife Research Center
Piedmont Widespread Northern Prairie Wildlife Research Center
Blue Ridge Mountains Widespread Northern Prairie Wildlife Research Center
    Great Smoky Mountains National Park           Yes Northern Prairie Wildlife Research Center
Ridge and Valley          Yes Northern Prairie Wildlife Research Center
Cumberland Plateau          Yes Northern Prairie Wildlife Research Center
Georgia Widespread Northern Prairie Wildlife Research Center
Clarke County, Georgia          Yes UGA Herbarium Specimens

    According to many sources, swamp milkweed grows in USDA zones 4a to 9a.  Click here to link to a site with a map explaining the USDA Plant Hardiness Zones.  Click here to link to a site illustrating where A. incarnata grows in the continental United States.

NATURAL HISTORY:
    As its common name implies, the swamp milkweed grows around wet environments.  The water requirement is from low to high.  It will tolerate poorly drained soil, but will grow better in  a moist but well drained area.  Full sun exposure and fertile soil are also needed to grow.  The sweet smelling flowers bloom from June to August and attract a lot of insects.  The shape of the flower requires that the insect walk through pollen masses before it can reach the nectar.  When the insect leaves, it carries with it pollen from that flower. When it lands on another flower of the same species, it brings about cross-pollination which is one way that A. incarnata reproduces.  By fall, the flowers are no longer there and are replaced with large, rough seed pods.  When the pods ripen and burst open, the wind scatters the seeds.  The seeds have tufts of hair to catch the wind that carries them to a new location.  Milkweeds can also reproduce vegetatively from its underground roots.  This is a type of self reproduction which the plant produces clones of itself.

HOW TO ENCOUNTER:
    Since the plant is known to grow in wet areas, you can find it on banks and flood plains of lakes, ponds and waterways, marshes, and swamps.  You can also find it growing on roadsides and in fields where the conditions are tolerable.  The best time to try to locate the plant would be from June to August, when it is in bloom.  If you are unfamiliar with identifying one, you would have a better chance of identifying it by its cluster of pink flowers.  The swamp milkweed is the only one of the milkweeds with flowers of this color.  When not in bloom, it can be mistaken for one of its close relatives of the milkweed family, since they could possibly grow in the same type of area.  Click here to learn more about the genus, Asclepias, and click here to learn more about the milkweed family, Asclepiadaceae.  Swamp Milkweed is also easy to grow and many gardeners like to use it in their meadow gardens, wildflower gardens, and as a perennial boarder.  Click here to link to a site that sells A. incarnata seeds if you are interested in making it an addition to your garden.  If you grow swamp milkweed, butterflies will come!  Click on the butterfly to find out other flowers that they like.


                                               
 


BIBLIOGRAPHY:

Baskin, Jerry M. "Milkweed." The World Book Encyclopedia. 1998

Brickell, Christopher. The American Horticulture Society Encyclopedia of Gardening Plants. Portland, Oregon: Timber Press, 1994.

Everett, T.H. Encyclopedia of Gardening. New York: Greystone Press, 1960.

Griffiths, Mark. Index of Garden Plants. Portland, Oregon: Timber Press, 1994.

Heywood, Vernon H. "Asclepias." Popular Encyclopedia of Plants. Cambridge: Cambridge University Press, 1982.

Huxley, Anthony. The New Royal Horticulture Society Dictionary of Gardening. New York: The Stockton Press, 1992.

"Milkweed." Encyclopedia Americana: International Edition. 1998.

Northern Prairie Wildlife Research Center. "Swamp Milkweed (Asclepias Incarnata)." Midwestern Wetland Flora. Online.

Parker, Helen. Eyewitness Garden Handbooks: Perennials. New York: DK Publishing, Inc., 1996.

Smith, Gertrude. "Milkweed." Collier's Encyclopedia. 1997.

Trehane, Piers. Index Hortensis: Perennials. Wimborne: Quarterjack Publishing, 1989.

Wright, Michael. The Complete Handbook of Garden Plants. New York: Facts On File, 1984.