Ovalleaf Milkweed - Asclepias ovalifolia
State Rank Reason (see State Rank above)
Known in the state from two sites in extreme eastern Montana. Additional information on population levels, threats and trends are needed.
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.
Southern Alberta, Saskatchewan, and Manitoba south to Wyoming, Nebraska, northern Iowa and Illinois to the upper peninsula of Michigan.
Observations in Montana Natural Heritage Program Database
Number of Observations:
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(Observations spanning multiple months or years are excluded from time charts)
Open pine woodlands, prairies and dry riparian terraces.
Ecological Systems Associated with this Species
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).
Threats or Limiting Factors
STATE THREAT SCORE REASON
Threat impact not assigned because threats are not known (MTNHP Threat Assessment 2021).
- Literature Cited AboveLegend: View Online Publication
- Colla, S., L. Richardson, and P. Williams. 2011. Bumble bees of the eastern United States. Washington, DC: USDA Forest Service, Pollinator Partnership. 103 p.
- Colla, S.R. and S. Dumesh. 2010. The bumble bees of southern Ontario: notes on natural history and distribution. Journal of the Entomological Society of Ontario 141:39-68.
- Koch, J., J. Strange, and P. Williams. 2012. Bumble bees of the western United States. Washington, DC: USDA Forest Service, Pollinator Partnership. 143 p.
- Plath, O.E. 1934. Bumblebees and their ways. New York, NY: Macmillan Company. 201 p.
- Thorp, R.W., D.S. Horning, and L.L. Dunning. 1983. Bumble bees and cuckoo bumble bees of California (Hymenoptera: Apidae). Bulletin of the California Insect Survey 23:1-79.
- Tripoldi, A.D. and A.L. Szalanski. 2015. The bumble bees (Hymenoptera: Apidae: Bombus) of Arkansas, fifty years later. Journal of Melittology 50: doi: http://dx.doi.org/10.17161/jom.v0i50.4834
- Williams, P., R. Thorp, L. Richardson, and S. Colla. 2014. Bumble Bees of North America. Princeton, NJ: Princeton University Press. 208 p.
- Additional ReferencesLegend: View Online Publication
Do you know of a citation we're missing?
- Heidel, B. L. 1996. Noteworthy collections - Montana. Madrono 43(3):436-440.
- Heidel, B.L. and K.H. Dueholm. 1995. Sensitive plant survey in the Sioux District, Custer National Forest, 1994, Carter County, Montana and Harding County, South Dakota. Unpublished report to the Custer National Forest. Montana Natural Heritage Program, Helena, Montana. 95 pp. plus appendices.
- Heidel, B.L., S.V. Cooper and C. Jean. 2000. Plant species of special concern and plant associations of Sheridan County, Montana. Report to U.S. Fish and Wildlife Service. Montana Natural Heritage Program, Helena, Montana. 96 p.
- Lesica, P., M.T. Lavin, and P.F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
- Lesica, P., M.T. Lavin, and P.F. Stickney. 2022. Manual of Montana Vascular Plants, Second Edition. Fort Worth, TX: BRIT Press. viii + 779 p.
- Vanderhorst, J.P., S.V. Cooper, and B.L. Heidel. 1998. Botanical and vegetation survey of Carter County, Montana. Unpublished report prepared for the Bureau of Land Management. Montana Natural Heritage Program, Helena. 116 pp. + app.