Whorled Milkweed (Horsetail Milkweed)

Asclepias verticillata

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Whorled milkweed flowers.
This cluster of whorled milkweed blossoms exemplifies the unique look of milkweed flowers, recognizable at a glance.
Family

Apocynaceae (dogbanes); formerly Asclepiadaceae (milkweeds)

Description

Whorled milkweed is an herbaceous perennial, usually unbranched but occasionally with a few branches toward the tip. Sap is milky. Flowers in the typical milkweed form, in small umbels arising from upper leaf nodes, white to greenish white, with 6–20 flowers per umbel. Blooms May–September. Leaves threadlike, soft, to 2 inches long, arising from many whorls on the stem, with 3–6 leaves per whorl. Fruits smooth, narrow pods less than 4 inches long, erect, bearing seeds that have a tuft of white hairs.

Similar species: Another Missouri milkweed, fourleaf milkweed (Asclepias quadrifolia) is also called whorled milkweed. It looks much different, with 2 or 4 lance-shaped to ovate leaves per node, and often has pinkish flowers. Also, it lives in open woods instead of upland prairies.

Size

Height: 8–24 inches.

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Photo of whorled milkweed plant.
Whorled Milkweed (Horsetail Milkweed)
Whorled milkweed has small white flowers in round clusters. The whorled leaves are soft and threadlike.

whorled_milkweed_flowers_8-17-15.jpg

Photo of whorled milkweed flower cluster.
Whorled Milkweed (Horsetail Milkweed)
The white or greenish flowers of whorled milkweed grow in small umbels, with 6–20 flowers per umbel.
Habitat and conservation

Occurs in upland prairies, savannas, glades, exposed ledges and tops of bluffs, and sometimes in dry upland forests; also pastures, roadsides, and railroads.

image of Whorled Milkweed Horsetail Milkweed distribution map
Distribution in Missouri

Scattered nearly statewide, but nearly absent from the Bootheel lowlands.

Status

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.

Human connections

Milkweeds have a long list of historical medicinal uses, and the milky sap (latex) was once explored as a potential source of rubber. Milkweeds are increasingly popular with native wildflower gardeners, because planting them can aid North America’s declining monarch butterfly populations.

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.