Plant of the Week

Range map of Asclepias viridiflora. States are colored green where the species may be found.

Asclepias viridiflora.
Plant with flowers. Photo © 2012 David D. Taylor.

Asclepias viridiflora.
Close up of flowers with ant. Photo © 2012 David D. Taylor.

Green Comet Milkweed (Asclepias viridiflora Raf.)

By David Taylor

Green comet milkweed is in the Asclepiadaceae (milkweed) family, one of about 115 milkweed species that occur in the Americas. Most species are tropical or arid land species. The genus name, Asclepias, commemorates Asklepios, the Greek god of medicine. Some of the milkweed species have a history of medicinal use including common milkweed, A. syriaca (wart removal and lung diseases), and butterfly weed, A. tuberosa (also known as pleurisy root; pleurisy and other lung disease). The specific epithet, viridiflora, means "green flower" in reference to the green color of the flowers. The common name comes from the shape of the flower that was fancied to resemble a comet with its head and tail.

This species like most milkweeds has a deep rootstock that helps the plant survive fire and drought. The plant grows to about 0.75 meters (2.5 feet) tall, sometimes taller, with 4 to 6 pairs of opposite leaves. Leaves are more or less elliptical and 5 to 8 centimeters (2 to 3 inches) long by 2.5 centimeters (1 inch) wide. The underside is lighter in color than the upper side and may have hairs on it. Flowers are green. Flowers are 7 to 9 millimeters (0.25 to 0.35 inches) long, and are borne dense hemispherical clusters at the top of the plant. The narrow, upright seedpods (follicles) are borne singly or in pairs. Broken leaves and stems produce milky latex.

This milkweed like most milkweeds produces copious amounts of nectar and is an important pollinator plant. The flowers have a sweet odor. Bees, wasps, flies, and ants can be seen on its flowers. Green comet milkweed is used as a food plant by monarch butterfly caterpillars. The plant often occurs in low densities and in some shade and this may make it harder for monarchs to find it.

Green comet milkweed is a species of moist to dry shaded roadsides, savanna, fields, and prairie. It tends to grow in light to moderate shade, but tolerates full sun. It is known from Montana south through Wyoming, Colorado, Arizona, New Mexico, east to Florida, north to New York and Massachusetts, then west to Montana. It is also known from British Columbia east to Ontario.

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Wheel milkweed, Asclepias uncialis.
Wheel Milkweed (Asclepias uncialis)