Plant of the Week

Map of the United States showing states. States are colored green where the wheel milkweed may be found.
Range map of the wheel milkweed. States are colored green where the wheel milkweed may be found.

wheel milkweed.
Wheel milkweed (Asclepias uncialis ssp. uncialis), Lake Pueblo State Park, southern Colorado. Photo by Steve Olson.

Wheel milkweed (Asclepias uncialis ssp. uncialis)

By Steve Popovich

Easily overlooked, this inches-tall perennial herb in the milkweed family (Asclepiadaceae) is inconspicuous, with its dainty pink flowers lying low to the ground. It flowers in early spring, when most botany enthusiasts are not yet in “wildflower walk” mode. However, unlike most milkweeds, wheel milkweed has a pleasant fragrance that carries across the landscape on warm, sunny days, allowing the visitor to home in on plants in full bloom.

This milkweed occurs in uplands of grasslands across the central and southern United States, where it is apparently rare, with only a few dozen sites known. It is therefore a “Sensitive Species” in the Forest Service’s Rocky Mountain Region, where only a few sites occur on National Grasslands. Most sites across the species’ range are small, usually numbering less than 50 plants. It is possible that more populations exist but remain undetected due to the inconspicuous habit and its early-blooming flowers.

Some explanation is needed to understand the intricate milkweed flower. It is highly modified for specialized pollination. There appears to be a whorl of floral organs between the petals and the stamens. This is called the corona, and each segment is called a hood. These structures assist pollinators in striking loose the pollen and carrying it unknowingly to the next flower.

When the grassland is just beginning to awaken, keep your nose alert for an unexpected fragrance, and look to see if you can find the wheel milkweed. Please do not pick the plants, and report you lucky find to the appropriate land manager!

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Western Poison-ivy (Toxicodendron rydbergii)