Milkweeds

It’s hard to go anywhere in the Southern Appalachians during the summer and not see several different types of milkweeds, so named because most have a milky sap in their leaves. The leaves and stems of many milkweeds also contain cardiac glycosides which, if eaten, are toxic to herbivores. Several of the milkweeds are host plants for Monarch Butterfly larvae (Danaus plexippus). The caterpillars are unaffected by the alkaloids and store them, protecting them from predators due to their bad taste. The alkaloids are retained in the adult butterflies, also providing them with protection. 

Weakley list 46 different milkweed species found in the southeastern United States. Those we see most commonly are shown below. Click on any picture to zoom.


Clasping Milkweed, Blunt-leaved Milkweed, Wavyleaf Milkweed (Asclepias amplexicaulis)

  • Location – Sandy fields & open woodlands; locally common
  • Flowers – Single umbel with pink-to-red/purple flowers with reflexed corolla lobes
  • Stem – Smooth, upright, unbranched
  • Leaves – Dark green, sessile, clasping, wavy, with a cream-colored central vein
  • Fruit – Smooth, spindle-shaped pod (follicle) containing seeds with tufts of hair
  • Derivation of Scientific Name: From the Greek god of healing, Asklepios, & the Latin amplexicaulis meaning “stem-clasping”

Poke Milkweed (Asclepias exaltata)

  • Location: Forest edges; common
  • Flowers: Drooping umbels with greenish-white flowers
  • Stem: Smooth, upright
  • Leaves: Thin, smooth, stalked, opposite
  • Fruit: Follicles are erect & smooth
  • Derivation of Scientific Name: From the Latin meaning “elevated” or “praised”

Swamp Milkweed (Asclepias incarnata)

  • Swamp Milkweed (Asclepias incarnata) PlantLocation: Marshes, swamps, & bogs; common
  • Flowers: Rose-pink in a single umbel
  • Stem: Tall, downy, rarely branched
  • Leaves: Narrow, lanceolate, & opposite
  • Fruit: Follicles are erect & smooth
  • Derivation of Scientific Name: From the Latin incarnatus meaning “flesh-colored”

Four-leaved Milkweed (Asclepias quadrifolia)

  • Location: Forests & forest margins; common
  • Flowers: White in umbels
  • Stem: Simple & unbranched
  • Leaves: Lowermost & upper leaves are opposite; larger middle leaves appear whorled
  • Fruit: Follicles are erect 
  • Derivation of Scientific Name: From the Latin meaning “four-leaved”

Common Milkweed (Asclepias syriaca)

  • Location: Meadows & roadsides; common
  • Flowers: Pink to greenish-white in multiple dense umbels; scented
  • Stem: Thick, simple & unbranched
  • Leaves: Large, thick, & opposite
  • Fruit: Follicles are large, erect on recurved stalks, with spiny protrusions
  • Derivation of Scientific Name: Linnaeus mistakenly thought the plant came “from Syria”

Butterfly Weed (Asclepias tuberosa)

  • Location: Dry fields & roadsides; common
  • Flowers: Bright orange/red; numerous in flat-topped umbels
  • Stem: Stout, hairy, branched at top, with many umbels
  • Leaves: Narrow, alternate, numerous, sap not milky
  • Fruit: Follicles are erect & smooth
  • Derivation of Scientific Name: Tuberosa means “from stems, referring to the plant’s habit of growing from a network of underground tubers

White Milkweed (Asclepias variegata)

  • Location: Forests & woodlands; common
  • Flowers: White with a purple center in a dense, flat-topped umbel
  • Stem: Stout, hairy, branched at top, with many umbels
  • Leaves: Broad, oval, opposite
  • Fruit: Follicles are erect & smooth
  • Derivation of Scientific Name: From the Latin meaning “varied” for its multi-colored flower

Photography by Jock Aplin, Ken Borgfeldt, Richard Holzman, Penny Longhurst, Jim Poling, Lucy Prim, & Joe Standaert

Sources

Natureworks – Monarchs

Namethatplant.org – Asclepias

https://www.fs.fed.us/wildflowers/plant-of-the-week/asclepias_syriaca.shtml

Gobotany – asclepias

Horn, Dennis & Cathcart, Tavia: Wildflowers of Tennessee the Ohio Valley and the Southern Appalachians. Lone Pine Publishing, 2005, p. 226.

Radford, Alfred E., Ahles, Harry E., & Be4ll, C. Ritchie: Vascular Flora of the Carolinas. University of North Carolina Press, 1968, p. 848. 

Singhurst, Jason, Hutchins, Ben, & Holmes, Walter C.: Identification of Milkweeds in Texas. Texas Parks & Wildlife Department. PWD RP W7000-1803 (06/15)

Smith, Richard M. Wildflowers of the Southern Mountains. University of Tennessee Press, 1998, p. 127.

Weakley, Alan S.: Flora of the Southeastern United States. Edition of 20 October, 2020, p. 1222.