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Montana Field Guide

Montana Field Guides

Lesser Rushy Milkvetch - Astragalus convallarius
Other Names:  Astragalus diversifolius [misapplied]

Species of Concern
Native Species

Global Rank: G5
State Rank: S3
(see State Rank Reason below)
State Threat Score: Medium - Low
CCVI: Moderately Vulnerable

Agency Status
USFS: Species of Conservation Concern in Forests (HLC)


External Links

State Rank Reason (see State Rank above)
The distribution of A. convallarius in Montana is limited to two disjuct localities in the state: the Helena Valley vicinity and an area in extreme southwest Montana in Beaverhead County. The species has been and continues to be negatively impacted by development in the Helena area. Past development in the Helena Valley likely eliminated extensive areas of previously occupied habitat resulting in the more fragmented distribution seen today. The grassland habitats this species occupies are also being invaded by several noxious weeds, partcularly in the Helena vicinity. However, the species appears to tolerate some levels of disturbance and degradation of habitat quality. Several large occurrences are presently known and some areas of potentially suitable habitat remain unsurveyed.
  • Details on Status Ranking and Review
    Lesser Rushy Milkvetch (Astragalus convallarius) Conservation Status Review
    Review Date = 10/25/2012
    View State Conservation Rank Criteria
    Population Size

    Score1 - Moderate: Generally 10,000-100,000 individuals.

    Range Extent

    Score1 - Peripheral, Disjunct or Sporadic Distribution in MT: Widespread species that is peripheral, disjunct or sporadically distributed within MT such that it occurs in <5% of the state (<7,500 sq. miles or the combined area of Beaverhead and Ravalli Counties) or is restricted to 4-5 sub-basins.

    Area of Occupancy

    Score1 - Moderate: Generally occurring in 11-25 Subwatersheds (6th Code HUC’s).

    Environmental Specificity

    Score1 - Moderate: Species is restricted to a specific habitat that is more widely distributed or to several restricted habitats and is typically dependent upon relatively unaltered, good-quality habitat (C Values of 5-7).

    CommentSpecies appears to be tolerant of some habitat disturbance and has been observed growing in areas planted/dominated with hard fescue.


    Score1-2 - Minor to Moderate Declines:

    CommentMonitoring data are lacking though development has directly impacted populations and habitat in the Helena Valley and surrounding area over the last few decades.


    Score1-2 - Medium to High.

    CommentWeed invasion, urban development and land-use activities in the Helena Valley and surrounding areas are impacting some populations and habitat. However, large areas of occupied habitat are in public ownership offering some degree of protection.

    Intrinsic Vulnerability

    Score0-1 - Low to Moderate Vulnerability.

    Raw Conservation Status Score

    Score 6 to 9 total points scored out of a possible 19.

General Description
Lesser Rushy Milkvetch is a slender herbaceous perennial with 1-6 erect to spreading stems, rising up to 5 dm high from a branching, underground rootcrown. The compound or simple leaves are 2-11 cm long with 0-5 pairs of thread-like leaflets. Leaflets of the upper leaves are usually lacking, giving them a grass-like appearance. Foliage is sparsely hairy to glabrous in the upper portion. Off-white or yellowish, pea-like flowers are sparsely scattered on stalks which are 2-14 cm long and arise from the axils of the upper leaves. The upper petal of each flower is 7-11 mm long and bent upward. The calyx is 4-6 mm long and sparsely covered with white or black hairs. Pendent, green or purple-mottled fruits are bean-shaped, 13-50 mm long, and 2-4 mm wide.

Flowering from June-early July, fruiting in late June-early August.

Diagnostic Characteristics
Only the typical variety of the species is known in the state. A. ceramicus looks similar in appearence but can be distinquished by the shorter calyx tube (2-3.5 mm long) and the inflated, oblong-ellipsoid pods, whereas the pods of A. convallarius are compressed and linear to oblong.

A. convallarius has sometimes been lumped with the species A. diversifolius.

Species Range
Montana Range Range Descriptions


Range Comments
ID, MT south to NV, UT and CO (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Observations in Montana Natural Heritage Program Database
Number of Observations: 101

(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)

Grasslands and open ponderosa pine woodlands in the valley and foothills. Festuca scabrella, Festuca idahoensis and Elymus spicatus are common bunchgrass associates.
Predicted Suitable Habitat Model

This species has a Predicted Suitable Habitat Model available.

To learn how these Models were created see

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 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).

Threats or Limiting Factors
Reported threats to Montana's populations of Lesser Rushy Milkvetch are related to urban activity because its habitat is concentrated around the Helena Valley (MTNHP Threat Assessment 2021). Several populations are presumed lost to urban development. While some populations are protected from direct land conversion, suitable habitat is increasingly lost to infrastructure and related fragmentation. Human activity threatens several extant populations where they are exposed to trampling from recreational hiking and off-highway vehicle (OHV) use is concentrated. Noxious weeds including Spotted Knapweed (Centaurea stoebe), Dalmatian Toadflax (Linaria dalmatica), and Leafy Spurge (Euphorbia virgata) occur with many populations, some of which are severe. Fire suppression poses another threat as Lesser Rushy Milkvech habitat will shrink as conifer canopy expands.

  • 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?
    • 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.
    • Quire, R.L. 2013. The sagebrush steppe of Montana and southeastern Idaho shows evidence of high native plant diversity, stability, and resistance to the detrimental effects of nonnative plant species. M.Sc. Thesis. Bozeman, MT: Montana State University. 124 p.
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Citation for data on this website:
Lesser Rushy Milkvetch — Astragalus convallarius.  Montana Field Guide.  .  Retrieved on , from