Milkweed Identification Guide

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 form large clones of up to several thousand stems (Wilbur, 1979). This means a patch of common milkweed could actually just be a single plant. Nectar composition in A. syriaca is nearly 100% sucrose (Southwick et al. 1981).  Monarchs often lay eggs on fresh shoots that are easier for caterpillars to feed on.

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).

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5 days and each flower produces about 1.5 uL of nectar each day, with a mean sucrose concentration of 30% (C.T. Ivey, unpublished data).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!

Tropical milkweed is an annual plant that is not native to the US (Woodson, 1954). It is native to Central and South America (Broyles and Stoj 2019). Electronic records show that tropical milkweed was planted in gardens in the US as early as 1806 (Satterfield et al., 2015). Tropical milkweed is self-compatible (Wyatt and Broyles 1997) so the plants can be fertilized with their own pollen.

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. 

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.

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.