South Dakota Native Plant Research
Asclepiadaceae: Asclepias incarnata

Asclepiadaceae: Asclepias incarnata


Download Seed: Brown seeds of swamp milkweed are 6.5-9 mm long. (60 KB)

Download Seedling of swamp milkweed two weeks after germination. (55 KB)

Download Older seedlings in the garden (1.2 MB)

Download Vegetative: The leaves are 6-15 cm long. (93 KB)

Download Flowering: The swamp milkweed produces numerous flowers in axillary and terminal umbels. (2.2 MB)

Download Fruiting: The swamp milkweed produces a follicle or pod in June-September. (784 KB)

Family Name


Common Name

Swamp milkweed

Native American Name

Lakota: wahíŋheya íphiye


Asclepias incarnata is a mostly solitary stemmed, upright, tall plant (70 to 200 cm) growing from a stout base and containing milky white sap. Usually, its stems have many branches toward the top. All portions of the plant contain a white milky juice. The mostly oppositely simple leaves are 5 to 15 cm long and 1 to 3 cm wide, ascending to spreading, narrow and lance-shaped, with the ends tapering to a sharp point and the margins entire. They are attached to the stem by a short petiole, 3-17 mm long. The inflorescences are terminal to the stem and branches, contain 10-40 flowers each attached by a short pedicel (10-17 mm) connected to a 1-7 cm peduncle. Flowers are 9-11 mm tall with 5-merous calyx has green to purple lobes 1.3-2.3 mm long. The petals are bright pink to rarely white, reflexed 5-6 mm long. The stamens and pistil are pink to white and fused, 1.2-1.8 mm tall and 1-1.5 mm wide. The fruit is an erect follicle 5-8 cm long. The seeds are broadly ovate 6-9 mm long and are covered with long white hairs. Swamp milkweed blooms from June through September and is commonly found in marshes, along banks of lakes, ponds and other waterways throughout South Dakota.

Additional Notes

Swamp milkweed is an important food source for the monarch butterfly caterpillar. The flowers attract butterflies, bumblebees and hummingbirds to the garden. Young shoots, leaves and seed pods are all edible if cooked. Extracting the milky latex is accomplished by placing plant materials in cold water and bringing them to a boil. They can then be steamed, boiled or fried.

Horticulture Notes

Seed Collection: Seeds turn brown and are released from the pods over an extended period. The seeds in open pods often have milkweed buds and care should be taken or they will consume stored seeds. Unopened brownish pods that split when gently squeezed are the best source.

Germination: Seeds require 30 days of cold moist stratification before planting in the spring. Seeds planted in the fall will germinate in the following spring.

Vegetative propagation: Established plants can be divided in late spring and transplanted.

Light: Full sun to partial shade.

Soil: Rich, wet to average garden moisture. Prefers neutral to slightly acidic soil but will tolerate heavy clay.

Asclepiadaceae: Asclepias incarnata