Wildflower Detectives: How to Distinguish Swamp Milkweed, Common Milkweed, and Spotted Joe-Pye Weed

Written by: Grace Bruckman 


It’s that time of year when everything seems to be in full bloom and the pollinators are working overtime. Milkweed plants are a vital component of the ecosystem, providing critical habitat and food for Monarch Butterflies (Danaus plexippus) and various other pollinators. Within the milkweed family, two common members, Swamp Milkweed (Asclepias incarnata) and Common Milkweed (Asclepias syriaca), often leave nature enthusiasts puzzled due to their similar appearances.


Furthermore, another important pollinator plant that often gets confused with milkweed is Spotted Joe Pye Weed (Eutrochium maculatum). This post will provide information on the distinct characteristics that set these three plants apart, allowing you to accurately identify them on your next nature walk.


Swamp milkweed (Asclepias incarnata)

Swamp milkweed is a sweetly fragrant, perennial plant that blooms from June to September. This plant is an important larval host to the Monarch Butterfly (Danaus plexippus) and Queen Butterfly (Danaus gilippus). Swamp Milkweed prefers full to partial sun in damp or moist areas close to wetlands, rivers, and lakes - usually not found in drier areas.


Identification features

Height: 3-5ft
Leaves: Opposite, simple, short, narrow, lance shaped (lanceolate) with smooth edges and a glossy appearance
Flowers: Clusters of 10-40 pink to purplish with five petals on each flower
Fruit: Seed pods are smooth
Stem: Branching at central stem


Links to more Information on Swamp Milkweed

Network of Nature - Swamp Milkweed 

Minnesota Wildflowers - Swamp Milkweed

Ontario Wildflowers - Swamp Milkweed

Prairie Pollination - Swamp Milkweed


Photo 1. Swamp Milkweed flower clusters and growth form



Common Milkweed (Asclepias syriaca)

Common Milkweed is a perennial plant with a unique floral fragrance that blooms June to August. This plant is also an important larval host to the Monarch Butterflies. Unlike Swamp Milkweed, this plant prefers sunny, open, dry areas and can often be found in ditches, meadows and roadsides.


Identification features

Height: up to 6ft
Leaves: Opposite, whorled, broad, oval shape with prominent central veins. Smooth on the top with small, soft, fuzzy hairs on the underside
Flowers: Pale pink to white dome-shaped flowers with 5 petals
Fruit: Large, green, prickly, ovate seedpods
Stems: Branching occurs only close to the flowers


Links to more information on Common Milkweed

Network of Nature -  Common Milkweed

Minnesota Wildflowers - Common Milkweed

Ontario Wildflowers - Common Milkweed 


Photo 2. Common Milkweed flower clusters and growth form. Monarch caterpillar feeding on Common Milkweed leaf. 


Similar species: Spotted Joe Pye Weed (Eutrochium maculatum)

Spotted Joe Pye Weed is a plant that attracts native pollinators and appears very similar to milkweed species. This plant tends to grow in wet and moist soils such as damp meadows, marshes and along the edges of rivers.


Identification features

Height: 4-7ft
Leaves: Whorls of 3-6 lance-shaped leaves
Flowers: Umbrella-like clusteres of small tubular pink to purplish-pink florets that form collectively in a dome
Stems: Sturdy purple stems with spotting
Fruit: No seed pods are formed. Flowers turn into small brown seeds


Links to more information on Spotted Joe Pye Weed

Network of Nature - Spotted Joe Pye Weed

Ontario Wildflowers - Spotted Joe Pye Weed

Minnesota Wildflowers: Spotted Joe Pye Weed


Photo 3. Spotted Joe Pye Weed flower clusters and growth form. 


Other Plant ID Resources 

Nature Watch - Identifying Milkweed

Go Botany - Plant ID Key

Ontario Wildflowers - Plant ID

OSU - Plant ID - Examining Leaves

Eat The Planet - A Guide to Identifying Plants


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