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Spiny Milkvetch - Astragalus kentrophyta var. kentrophyta

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Native Species

Global Rank: G5T4
State Rank: S2S4
(see State Rank Reason below)

Agency Status


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State Rank Reason (see State Rank above)
Astragalus kentrophyta variety kentrophyta is a Great Plains species that is uncommon across eastern and north-central Montana. Variety kentrophtya is long-lived and grows in sandy or gravelly soil in prairies, often around alkaline ponds. In Glacier County varieties kentrophyta and tegetarius can co-occur. Livestock have been observed to avoid this plant. Current information on locations, population sizes, threats, and reproduction are greatly needed to refine its status in Montana.
  • Details on Status Ranking and Review
    Spiny Milkvetch (Astragalus kentrophyta var. kentrophyta) Conservation Status Review
    Review Date = 07/15/2020
    View State Conservation Rank Criteria
    Range Extent

    ScoreF - 20,000-200,000 sq km (~8,000-80,000 sq mi)

    Comment39,629 sq km to 44,045 square kilometers for 5 to 8 observations.

    Area of Occupancy

    ScoreC - 3-5 4-km2 grid cells

    CommentMontana can be divided into 30,390 4x4 square kilometer cells. For this species plant observations occur in 5 of these 4x4 square kilometer cells.

    Number of Populations

    ScoreB - 6 - 20

    CommentBased on herbarium records and botanist observations at least 11 observations are known or suspected.

    Environmental Specificity

    ScoreD - Broad. Generalist or community with all key requirements common


    ScoreD - Low

    CommentPotential that habitat could be threatened. Livestock are not a threat though.

General Description
PLANTS: A mat-forming perennial plant that grows from an intricately branched caudex. Hairs on plant are strigillose (stiff, straight, sharp, and appressed) to villous (long, soft, crooked, and not tangled). Stems prostrate with upper ends ascending 1–3 cm. Source: Lesica et al. 2012.

LEAVES: Leaves alternately arranged on the stem and pinnately divided into 3 to 7 leaflets. Leaflets are narrowly lanceolate in shape, 3–9 mm long, and with mucronate tips. Terminal leaflet is confluent with the rachis of the leaf. Stipules are 2–5 mm long, sessile (basally connate). Source: Lesica et al. 2012.

INFLORESCENCE: Raceme of 1 to 3 flowers growing in the axils of a leaf and shorter than the leaves. Papilionaceous flowers: Petals are white to purple; Banner is reflexed, 4–8 mm long; and Keel is 3–7 mm long. Sepals are green with white and/or black strigillose hairs, 1-3 mm long. Legume is ovoid, compressed, strigose, and 3–5 mm long. Source: Lesica et al. 2012.

VARIETY kentrophyta: Hair Types are mixed with both basifixed and dolabriform hairs present. Flowers are 4-5 mm long. Petals are mostly white. Source: Lesica et al. 2012.

Astragalus is derived from the Greek word for ankle bone, astragalos which may refer to the shape of the leaves or fruits (legumes) (Giblin et al. [eds.] 2018).

Diagnostic Characteristics
Astragalus kentrophyta has two varieties in Montana:

Variety tegetarius
*Hair Type: Only the basifixed (hair attached at one end to the epidermis) type is present on the plant.
*Flowers: Mostly purple and at least 5 mm long.
*Habitat: Fellfields, moraine, and scree near or above treeline.

Variety kentrophyta
*Hair Types: Both basifixed (hair attached at one end to the epidermis) and dolabriform (hair attached near its middle to the epidermis; like a seesaw) types are present on the plant.
*Flowers: Mostly white and 4-5mm long.
*Habitat: Sandy or gravelly soil, often around ponds in the plains.

Species Range

Range Comments
Astragalus kentrophyta is found in Alberta and Saskatchewan, Canada south to California, Arizona, New Mexico, and Nebraska, United States (Lesica et al. 2012). Variety kentrophyta has been found in eastern and north-central Montana.

NOTE: The Montana maps below only reflect observations reported at the variety-level for kentrophyta.

Observations in Montana Natural Heritage Program Database
Number of Observations: 5

(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)

Sandy or gravelly soil, often around ponds in the plains zone of Montana (Lesica et al. 2012).

In eastern Glacier County, varieties kentrophyta and tegetariushave been found co-occurring in mixed grass prairie with Bouteloua gracilis, Festuca idahoensis, and Elymus smithii where soils are gravelly, silty, and well-drained (Tara Luna personal communication). Habitat was observed as being of good to excellent quality.

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
Plants reproduce by seed. Seeds have the potential for long term viability in natural seedbanks (Tara Luna personal communication). In eastern Glacier County it has been observed that plants do not flower and reproduce during drought conditions (Tara Luna personal communication).

*Species belonging to the Pea Subfamily (Papilionoideae) have papilionaceous flowers (Elpel 1998). This applies to almost all species in the northern latitudes (Elpel 1998).
*It refers to the petals of the flowers appearing like a butterfly.
*The 5 petals (collectively called the corolla) have a bilateral symmetry: large upper petal (banner), two lateral petals (wings), and usually two fused lower petals (keeled). The keel petals resembling a boat.

In north-central Montana livestock have been observed to avoid plants.

  • 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.
    • Elpel, Thomas. 2000. Botany In A Day, Elpel's Herbal Field Guide to Plant Families. 4th Edition, January. Hollowtop Outdoor Primitive School Press, Pony, Montana.
    • Giblin, David E., Ben S. Legler, Peter F. Zika, and Richard G. Olmstead (editors). 2018. Flora of the Pacific Northwest: An Illustrated Manual. Second Edition. University of Washington Press in Association with Burke Museum of Natural History and Culture, Seattle, Washington. 882 pp.
    • 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?
    • Ament, R.J. 1995. Pioneer Plant Communities Five Years After the 1988 Yellowstone Fires. M.Sc. Thesis. Bozeman, MT: Montana State University. 216 p.
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Citation for data on this website:
Spiny Milkvetch — Astragalus kentrophyta var. kentrophyta.  Montana Field Guide.  .  Retrieved on , from