Green-Flowered Milkweed (Spider Milkweed; Ozark Milkweed)

Asclepias viridis

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Photo of green-flowered milkweed showing flowers and leaves.
The flower clusters of green-flowered or spider milkweed bear large flowers with greenish-yellow petals and purple hoods.
John D. Byrd, Mississippi State University, Bugwood.org
Family

Apocynaceae (dogbanes); formerly Asclepiadaceae (milkweeds)

Description

Herbaceous perennial, erect or spreading, sometimes few-branching toward the tip. Sap milky. Flowers large for a milkweed, some reaching 1 inch wide, with green or greenish-white petals that spread upward (not back) and hoods (the upper part of the flower) violet to purple. Flowers in one or a few round clusters at the tops of the plant, with 3–20 flowers per cluster. Blooms May–June. Leaves alternate, on very short stalks, broadly oblong, narrowing toward the base, to 4½ inches long. Fruits smooth, erect pods, lance-shaped to oval in outline, to 5 inches long, bearing seeds each with a tuft of white or whitish hairs.

Size

Height: 8–24 inches.

green-flowered_spider_milkweed_flower_cluster_8-17-15.jpg

Photo of green-flowered milkweed closeup on flower cluster.
Green-Flowered Milkweed (Spider Milkweed; Ozark Milkweed)
Green-flowered milkweed is visited by many insects, which drink nectar from the flowers and pollinate the plant.

green-flowered_spider_milkweed_in_prairie_8-17-15.jpg

Photo of green-flowered milkweed blooming in a prairie.
Green-Flowered Milkweed (Spider Milkweed; Ozark Milkweed)
Green-flowered or spider milkweed occurs in upland prairies and glades and along roadsides and railroads.

green-flowered_spider_milkweed_flower_8-17-15.jpg

Photo of green-flowered milkweed, closeup of single flower.
Green-Flowered Milkweed (Spider Milkweed; Ozark Milkweed)
Unlike most other milkweeds, the petals of green-flowered milkweed spread upward and are not reflexed backward.
Habitat and conservation

Occurs in upland prairies and glades, usually on calcareous substrates; also along roadsides and railroads.

Distribution in Missouri

Scattered mostly south of the Missouri River.

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

In bloom, this is a dazzling plant. Native wildflower gardeners are growing more milkweeds in order to help monarch butterflies, whose populations are declining. Milkweeds have a long list of historical medicinal uses. They have had many other uses, too.

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.