Montana Field Guide

Ovalleaf Milkweed is a rhizomatous perennial with usually solitary slender stems 2-6 dm high. The erect to spreading, opposite leaves have petioles which are up to 1 cm long, and broadly lance-shaped to elliptic blades which are 4-8 cm long with entire margins. Leaves are moderately long, hairy beneath, and the sap is milky. 1-3 umbrella-shaped, stalked clusters of 8-20 flowers are at the top of the stem or in the axils of the upper leaves. Each greenish-white to cream flower is 8-10 mm high and borne on a hairy stalk that is up to 20 mm long. Flowers have 5 reflexed corolla lobes which are 5-6 mm long, and 5 erect hoods which are 4-5 mm long and rounded at the tip; these hoods surround a greenish or yellowish central column, and each has a conical horn inside. The erect spindle-shaped fruits are 6-8 cm long and ca. 1 cm wide. Each fruit has numerous seeds, each with a light brown tuft of hairs that is 18-35 mm long.

Flowering in late June-early July.

Asclepias viridiflora and A. speciosa also have broad leaves, but the former lacks horns within the hoods, and the latter has pink to purple flowers.

Open pine woodlands, prairies and dry riparian terraces.

POLLINATORS
The following animal species have been reported as pollinators of this plant species or its genus where their geographic ranges overlap: Bombus vagans, Bombus huntii, Bombus rufocinctus, Bombus ternarius, Bombus terricola, Bombus pensylvanicus, Bombus bimaculatus, Bombus griseocollis, Bombus impatiens, Bombus insularis, and Bombus flavidus (Plath 1934, Heinrich 1976, Thorp et al. 1983, Colla and Dumesh 2010, Colla et al. 2011, Koch et al. 2012, Williams et al. 2014, Tripoldi and Szalanski 2015).

STATE THREAT SCORE REASON
Threat impact not assigned because threats are not known (MTNHP Threat Assessment 2021).