Plant of the Week
Oval-leaved Milkweed (Asclepias ovalifolia)
By Christopher David Benda
Oval-leaved milkweed is a perennial plant in the Milkweed family (Asclepiadaceae). The genus name “Asclepias” refers to the Greek god of medicine Asklepios, while “ovalifolia” refers to the oval-shaped leaves.
This lesser known milkweed species blooms in late May to early July. The flowers are white and produced in several umbels. Fertilized flowers produce erect follicles (seed pods) that are covered in fine hairs and held erect. The plant is upright, but short, and has just a few pairs of oval leaves along the stem. The leaves are on short stalks and have no teeth along the margins. Like most milkweeds, this species is monoecious and produces milky sap in its tissues. The milky sap is toxic and contains cardiac glycosides, but a number of animals have developed defenses that allow them to eat the plant without harm.
In general, milkweed flowers are highly specialized. The flower is comprised of the central corona with five surrounding circular structures called hoods, each with a curved projection called a horn, and five reflexed petals that point downward. Like many of the rare milkweeds, little is known about the pollinators that visit the flowers.
A plant of prairies and savannas, this species is rare in the eastern portion of its range in Illinois and Wisconsin, but more prevalent, although still uncommon, in Iowa, Minnesota, and the Dakotas. It is mostly found in remaining high quality natural areas. It prefers open sun and frequent wildfire.