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Montana Field Guide

Montana Field Guides

Woollypod Milkvetch - Astragalus purshii var. purshii

Native Species

Global Rank: G5T5
State Rank: S4S5

Agency Status


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General Description
PLANTS: A short, perennial forb from a branched caudex. The nearly leafless stems (acaulescent) are prostrate, 5–10 cm, clothed in stipules. Herbage is wooly-villous which gives the plant a silvery-grey appearance

LEAVES: Pinnately compound leaves are about 12 cm long, weakly ascending or erect. The 9-13 leaflets are oval-orbicular, oblanceolate to lanceolate with rounded to acute tips. Stipules are lanceolate, 3–10 mm long, and separate from each other.

INFLORESCENCE: A short, tightly congested raceme that appears somewhat umbellate-like and terminates a leafless peduncle, usually less than 10 cm long. The inflorescence of 3-10 flowers is erect, about as tall as the leaves, but often lays on the ground in fruit. Flowers are 18-25 mm long. Petals are either
dull white except for the purple tinged keel tip (seldom is the banner and wing tips lavender) or magenta. The banner petal is 18–25 mm long and moderately reflexed. The keel petal is 15–20 mm long. Sepals are 2–5 mm long with black and/or white villous hairs>

Montana’s plants are of variety purshii or concinnus.

Sources: Lesica et. al 2012; Giblin et al. [eds.] 2018.

Diagnostic Characteristics
In Montana Astragalus purshii has two varieties (Lesica et al. 2012):

* var. purshii has creamy-white to pale lavendar flowers (petals) that are 18-25 mm long. The legumes are nearly straight. It is found in grasslands and sagebrush steppe in the plains and valley zones of Montana.

* var. concinnus has magenta flowers (petals) that are 18-20 mm long. Legumes are curved. It is mostly found in the sagebrush steppe of the montane zone within southwest Montana.

Species Range

Range Comments
BC to MB and the Dakotas south to CA, NV, UT and CO (Kartesz 2009).

Observations in Montana Natural Heritage Program Database
Number of Observations: 13

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)

Var. purshii is found in grasslands and sagebrush steppe in the plains and valley zones of Montana.

The following animal species have been reported as pollinators of this plant species or its genus where their geographic ranges overlap: Bombus vagans, Bombus appositus, Bombus auricomus, Bombus bifarius, Bombus borealis, Bombus centralis, Bombus fervidus, Bombus flavifrons, Bombus huntii, Bombus mixtus, Bombus nevadensis, Bombus rufocinctus, Bombus ternarius, Bombus terricola, Bombus occidentalis, Bombus pensylvanicus, Bombus griseocollis, and Bombus insularis (Macior 1974, Thorp et al. 1983, Mayer et al. 2000, Colla and Dumesh 2010, Wilson et al. 2010, Koch et al. 2012, Miller-Struttmann and Galen 2014, Williams et al. 2014).

Reproductive Characteristics
FRUIT [Source: Lesica et al. 2012]
The ovary has dense, long, and soft hairs. The legume is 12-25 mm long, retains the dense long hairs, and is tipped with a sharp beak. The legume is also narrowly ovoid (compressed perpendicular to the septum) in shape.

  • Literature Cited AboveLegend:   View Online Publication
    • 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.
    • Lesica, P., M.T. Lavin, and P.F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
    • Macior, L.M. 1974. Pollination ecology of the Front Range of the Colorado Rocky Mountains. Melanderia 15: 1-59.
    • Mayer, D.F., E.R. Miliczky, B.F. Finnigan, and C.A. Johnson. 2000. The bee fauna (Hymenoptera: Apoidea) of southeastern Washington. Journal of the Entomological Society of British Columbia 97: 25-31.
    • Miller-Struttmann, N.E. and C. Galen. 2014. High-altitude multi-taskers: bumble bee food plant use broadens along an altitudinal productivity gradient. Oecologia 176:1033-1045.
    • 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.
    • Williams, P., R. Thorp, L. Richardson, and S. Colla. 2014. Bumble Bees of North America. Princeton, NJ: Princeton University Press. 208 p.
    • Wilson, J.S., L.E. Wilson, L.D. Loftis, and T. Griswold. 2010. The montane bee fauna of north central Washington, USA, with floral associations. Western North American Naturalist 70(2): 198-207.
  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Sater, S. 2022. The insects of Sevenmile Creek, a pictorial guide to their diversity and ecology. Undergraduate Thesis. Helena, MT: Carroll College. 242 p.
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Citation for data on this website:
Woollypod Milkvetch — Astragalus purshii var. purshii.  Montana Field Guide.  .  Retrieved on , from