Swamp milkweed has pink flower clusters at the tips of its tall stalks. The leaves are opposite, narrow, and up to 6 inches long. It grows in moist bottomland soils.
Swamp milkweed is a perennial herb. The stems are smooth, tall, flexible, and branching. The sap is a milky latex.
The flowers are mostly terminal (positioned at the tops of the stems), in many loose umbels (each rounded cluster arising from the same point); pink or rarely white, with a delicate fragrance.
Blooms June–September.
The leaves are mostly opposite, narrowly lance-shaped, to 6 inches long and about 1 inch wide.
The fruits are slender pods, to 4 inches long, in pairs, smooth but usually slightly hairy, bearing seeds with silky parachutes.
Similar species: Swamp milkweed can be distinguished from similar milkweeds by its pink-flowered flower clusters positioned at the tops of the plant stalks (not arising from the sides of the stems), relatively narrow leaves, and moist bottomland habitat.
Learn more about Missouri's milkweeds on their group page and on the several other individual species pages in this guide.
Height: to 6½ feet.
Scattered nearly throughout the state.
Habitat and Conservation
Occurs in moist, open bottomlands, especially in the Missouri and Mississippi floodplains, where it is often the dominant plant. Look for it in swamps, sloughs, marshes, margins of ponds and lakes, banks of streams and rivers, bottomland prairies, and occasionally bottomland forests; also ditches and railroads.
Status
Native Missouri wildflower. Gaining in popularity as a native landscaping plant, since its delicate pink flowers are showy, and it helps monarchs and other native insect pollinators.
Human Connections
Because they are a required larval food plant of monarchs, milkweeds are increasingly popular with native plant gardeners concerned about the decline of those butterflies, and swamp milkweed is a favorite for this.
Ecosystem Connections
The roots are eaten by muskrats and other wetland mammals. The young shoots and leaves are also browsed by rabbits and deer.
Monarch butterflies use milkweeds as larval food plants, collecting the sap’s toxic cardiac gycosides in their bodies and becoming unpalatable to predators. Several other kinds of insects are also specialized for feeding on milkweeds, and they, too, gain immunity from predators.
Many insects visit the flowers for nectar.
The entire former milkweed family (Asclepiadaceae) has recently been rolled into the dogbane family (Apocynaceae). For many years, botanists have known the two families were closely related. The milkweed group, with its distinct floral structures, is still considered a unique subfamily or tribe of the dogbane family. As you consult various sources, you can expect to see milkweeds grouped in either family.
