Prairie Milkweed (Tall Green Milkweed)

Asclepias hirtella

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Photo of prairie milkweed plant in flower.
Prairie milkweed has full, rounded clusters of small, delicately purple-tinged flowers.
Family

Apocynaceae (dogbanes); formerly Asclepiadaceae (milkweeds)

Description

Prairie milkweed is a perennial herb, sometimes with a few branches toward the tip, with hairy stems and flower stalks. Sap milky. Flowers in stalked umbels (rounded clusters) arising from the upper leaf axils, with 25–90 flowers per umbel; each flower quite small, with pale green petals, the reflexed petals often purple-tinged with white edges. Blooms May–August. Leaves narrow, lance-shaped, with prominent side veins on the underside; arrangement alternate, but so crowded as to appear opposite or whorled. Fruits smooth, minutely hairy, ascending pods on descending stalks, to 5 inches long, containing seeds having white, cream-colored, or tan silky hairs.

Size

Height: 1–3 feet.

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Photo of prairie milkweed, or tall green milkweed, fruits.
Prairie Milkweed (Tall Green Milkweed) (Fruits)
Prairie milkweed, like most other milkweeds, bears pods holding numerous seeds, each with a parachute of silky hairs.

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Photo of prairie milkweed view of stalk with rows of leaves
Prairie Milkweed Leaves
Prairie milkweed stalks have an interesting geometry, with crowded arrangements of narrow, lance-shaped leaves.

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Photo of a monarch caterpillar eating prairie milkweed flowers
Monarch Caterpillar on Prairie Milkweed Flower Cluster
Prairie milkweed, and other milkweeds, are important food plants for the declining monarch butterfly.

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Photo of a prairie milkweed plant blooming amid other prairie vegetation
Prairie Milkweed Blooming at Friendly Prairie
The distinctive stalks of prairie milkweed contribute to the impressive array of vegetation forms and textures on native prairies.

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Photo of prairie milkweed plant in flower.
Prairie Milkweed (Tall Green Milkweed)
Prairie milkweed occurs in bottomland and upland prairies and glades as well as pastures, roadsides, and railroads.

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Photo of prairie milkweed plant in flower.
Prairie Milkweed (Tall Green Milkweed)
Prairie milkweed is scattered mostly in the northwestern two-thirds of the state.
Habitat and conservation

Occurs in bottomland and upland prairies and glades as well as pastures, roadsides, and railroads.

Distribution in Missouri

Scattered mostly in the Glaciated and Unglaciated Plains, which is basically the northwestern two-thirds of the state. Mostly absent from the Ozarks and Bootheel.

Status

The entire former milkweed family (Asclepiadaceae) was fairly recently rolled into the dogbane family (Apocynaceae). For many years, botanists knew 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.

Human connections

Milkweeds have a long list of historical medicinal uses. They are being planted more and more in order to help the declining monarch butterfly populations. This species, with its subtle colors yet exciting round floral clusters, can be a showpiece in native wildflower gardens.

Ecosystem connections

Many bees, butterflies, and skippers drink nectar from the flowers, and crab spiders often hide in the clusters, hunting them. Monarch butterflies use milkweeds as larval food plants, collecting the sap's toxic cardiac gycosides in their bodies and becoming unpalatable to predators.