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Milkweed Identification Guide

 

There are around a 100 native species of milkweed in North America and we are not going to cover the details to identify all of them. However, we offer some tips to identify some of the most common milkweed species used by volunteers. If you are unsure as to which species of milkweed you have at your garden, use the following photos and key characters to determine if you have any of these common milkweed species at your site. Please, be sure to mark them on your data sheet! 

 

If you are looking where to buy milkweed plants that are good to use at your particular ecoregion, we suggest you check out the Milkweed Market and their list of vendors.

 
 
 
 

Common Milkweed (Asclepias syriaca)

Common Milkweed is a native perennial of the eastern United States and southern Canada, though it is found most commonly in the northeast and the midwest. It can be found in upland fields, woodland margins and disturbed areas such as roadsides (Wilburg, 1979). It prefers well-drained soils. Common milkweed can spread highly efficiently by shooting out rhizomes that can large clones of up to several thousand stems (Wilbur, 1979). This means a patch of common milkweed could actually just be a single plant.  Monarchs often lay eggs on fresh shoots that are easier for caterpillars to feed on.

Key Characteristics of Common Milkweed, Asclepias syriaca:

  • Flower color ranges from pink to white, highly fragrant

  • Milky sap when leaves/stem broken

  • Fine hairs on underside of leaves—soft and velvety!

  • Mature leaves typically quite broad

Butterfly Weed (Asclepias tuberosa)

Butterfly weed is a native perennial found across the eastern United States. It is well loved by butterflies for its brightly colored flowers and abundant nectar supply.  It is typically found in fields with drier soil and often grows in clumps. The stems are distinct because they are very hairy; however, unlike other milkweeds it doesn’t have a milky sap when broken. Butterfly weed will usually bloom two to three years after germination and can persist for 20 years or longer (Woodson, 1947).

Key Characteristics of Butterfly Weed, Asclepias tuberosa:

  • Flower color ranges from orange to yellow

  • Typically grow in clumps, stalks 1-3’ tall

  • NO milky sap is present

  • Very hairy stems

Swamp Milkweed (Asclepias incarnata)

Swamp Milkweed is a native perennial of the eastern and central United States and southern Canada (Manitoba, Quebec, and Nova Scotia). It is common in wetlands. Swamp milkweed will often have multiple stems up to 2 m tall and it can have several stems coming from one single root crown (Ivey et al., 2003). Each stem on average can have 22 pink flowers (Ivey et al., 2003). Flowers will last about 5 days and each flower produces about 1.5 uL of nectar each day, with a mean sucrose concentration of 30% (C.T. Ivey, unpublished data). Monarchs often lay eggs on fresh shoots that are easier for caterpillars to feed on. Swamp milkweed can spread highly efficiently by shooting out rhizomes. This means a patch of Swamp milkweed could actually just be a single plant!

Key Characteristics of Swamp Milkweed (Asclepias incarnata)

  • Flower color ranges from pink to light purple, fragrant

  • Produces milky sap when leaves/stem broken

  • Leaves are generally smooth, long, and narrow, tapering to a point

  • Prefers wet ground

Tropical Milkweed (Asclepias curassavica)

Tropical milkweed is native to Central and South America. Its striking flowers and easy propagation have increased its popularity in the US in spite of the fact that it is non-native. In colder climates that experience hard freezes, tropical milkweed will die back; however, in warmer southern climates it is able to persist year round. It is also known to have a longer flowering period than other winter-hardy milkweeds. Avoid buying this plant if possible. 

Key Characters of Tropical Milkweed, Asclepias curassavica:

  • Flowers with orange corona and red corolla

  • Produces milky sap when leaves/stem broken

  • Leaves narrow and pointed

  • Prefers moist soils and thrives in disturbed areas (but is typically found in gardens)

Showy Milkweed (Asclepias speciosa)

Showy milkweed is native to the western United States and is typically found in prairies and savannas. It is known for its long blooming period, drought tolerance and easy propagation.

Key characteristics of Showy Milkweed, Asclepias speciosa:

  • Broad, velvety leaves similar to common milkweed (can be distinguished by presence of white hairs)

  • Flower color ranges from light pink to purple

  • Fragrant flowers that resemble stars

Antelope Horns Milkweed (Asclepias asperula)

Antelope horns milkweed is native to the western United States and is found in savannas and prairies. Its name comes from the curved shape of the seedpods that often resembles antelope horns.

Key characteristics of Antelope Horns Milkweed, Asclepias asperula:

  • Greenish-yellow flowers with maroon accents

  • Clump forming, upright or sprawling

  • Long, narrow leaves that often fold in on themselves

  • Leaves irregularly grouped

  • Stems covered in tiny hairs

 
 
Literature Cited
Ivey, C., Martinez, P., and Wyatt, R. 2003. Variation in pollinator effectiveness in swamp milkweed, Asclepias incarnata (Apocynacea). American Journal of Botany, 90 (2):214-225.
Woodson, R.E., 1947. Some dynamics of the leaf variation in Asclepias tuberosa. Annals of the Missouri Botanical Garden, 34 (4):353-432.

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