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Gray's Milkvetch - Astragalus grayi
State Rank Reason (see State Rank above)
Rare in the state. Locally restricted to Carbon and Big Horn counties. Population levels, trends and threats to the species are poorly documented. Additional information is needed for the species within Montana.
- Details on Status Ranking and Review
Population Size
Score2 - Small: Generally 2,000-10,000 individuals.
Range Extent
Score2 - Regional or State Endemic or Small Montana Range: Generally restricted to an area <100,000 sq. miles (equivalent to 2/3 the size of Montana or less) or Montana contributes 50% or more of the species’ range or populations OR limited to 2-3 Sub-basins in Montana.
CommentRegional endemic of Wyoming, extending into south-central Montana. Documented from 3 sub-basins in Montana.
Area of Occupancy
Score2 - Low: Generally occurring in 4-10 Subwatersheds (6th Code HUC’s).
Environmental Specificity
Score1-2 - Moderate to High.
Trends
ScoreNA - Rank factor not assessed.
Threats
Score1 - Medium: 11-30% of the populations are being negatively impacted or are likely to be impacted by one or more activities or agents, which are expected to result in decreased populations and/or habitat quality and/or quantity.
CommentSeveral populations are near or adjacent to roads and may be impacted by associated activities.
Intrinsic Vulnerability
Score0-1 - Low to Moderate Vulnerability.
Raw Conservation Status Score
Score
8 to 10 total points scored out of a possible 16 (Rarity factors and threats only).
General Description
Gray's Milkvetch is an herbaceous perennial with numerous, simple or branched stems, 20-35 cm long and arising together from a branched rootcrown just below the ground. Alternate, pinnately compound leaves are 4-10 cm long with 3-11 wire-like leaflets. Leaves are rather stiff and often held erect or ascending. Foliage is thinly covered with long hairs. Unbranched inflorescences, 2-7 cm long, arise from the axils of upper leaves and have 9-27 somewhat congested, ascending flowers. Cream-colored, pea-like flowers have a partly reflexed upper petal that is 15-23 mm long and a calyx that is 6-10 mm long and thinly to densely covered with long white or black hairs. Oblong pods are green and fleshy, glabrous, round in cross section, and 9-18 mm long.
Phenology
Flowering and fruiting in June.
Diagnostic Characteristics
The combination of narrow, wire-like leaflets, no wider than the axis of the leaf, and erect stems and fruits is diagnostic. Astragalus pectinatus has similar foliage, but the pods are deflexed, and the stems often lie on the ground.
Species Range
Montana Range
Range Descriptions
Native
Range Comments
South-central MT and western WY. Regional endemic.
Observations in Montana Natural Heritage Program Database
Number of Observations: 24
(Click on the following maps and charts to see full sized version)
Map Help and Descriptions
Relative Density
Recency
(Observations spanning multiple months or years are excluded from time charts)
Habitat
Open soil in sagebrush steppe in the valley zone.
Ecological Systems Associated with this Species
Ecology
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 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).
Stewardship Responsibility
Threats or Limiting Factors
STATE THREAT SCORE REASON
Threat impact not assigned because threats are not known (MTNHP Threat Assessment 2021).
References
- 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.
- 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.
- MTNHP Threat Assessment. 2021. State Threat Score Assignment and Assessment of Reported Threats from 2006 to 2021 for State-listed Vascular Plants. Botany Program, Montana Natural Heritage Program, Helena, Montana.
- 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?- Barneby, R.C. 1964. Atlas of North American Astragalus. 2 Vols. New York Botanical Garden, Bronx, New York. 1188 pp.
- Lesica, P. and P.L. Achuff. 1992. Distribution of vascular plant species of special concern and limited distribution in the Pryor Mountain desert, Carbon County, Montana. Unpublished report to the Bureau of Land Management. Montana Natural Heritage Program, Helena, MT. 105 pp.
- 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.
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