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Montana Field Guide

Montana Field Guides

Small Onion - Allium parvum

Species of Concern
Native Species

Global Rank: G5
State Rank: S3
(see State Rank Reason below)
State Threat Score: Very High - High

Agency Status


External Links

State Rank Reason (see State Rank above)
Known from southwest Montana, primarily on the Bitterroot National Forest. Many of the the documented occurrences have large numbers of individuals and cover extensive areas. However, many of the sites are also infested with spotted knapweed and/or cheatgrass and continued increases in the density and spread of both invasive weeds are likely, further degrading the habitat occupied by Allium parvum.
  • Details on Status Ranking and Review
    Small Onion (Allium parvum) Conservation Status Review
    Review Date = 06/11/2012
    View State Conservation Rank Criteria
    Population Size

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

    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).


    Score0-1 - Stable to Minor Declines:

    CommentTrends are undocumented, though populations are likely stable or experiencing only minor declines.


    Score1-2 - Medium to High.

    CommentInvasive species and associated control efforts are the primary threats.

    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
Bulbs usually ovoid; outer coat membranous mostly without reticulations. Scapes flattened, 3–6 cm. Leaves 2, flat, falcate, 1–4 mm wide, persistent. Umbel congested-hemispheric with 5 to 30 flowers; pedicels 5–10 mm long; bracts 2, ovate, acute to acuminate. Flowers: tepals white with a purple midvein; 8–12 mm long; ovary with 3 crests adjacent to the style; stamens included. Seed surface smooth (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Flowering in late May-June.

Diagnostic Characteristics
The flattened stem and fine-textured bulb coats separate this species from the similar A. simillimum, A. textile and A. brandegeei.

Species Range
Montana Range Range Descriptions


Range Comments
Eastern OR to CA, east to ID, NV, and southwest MT. Peripheral.

Observations in Montana Natural Heritage Program Database
Number of Observations: 196

(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)

Dry, open forests, woodlands, or grasslands on warm slopes in the montane zone.
Predicted Suitable Habitat Model

This species has a Predicted Suitable Habitat Model available.

To learn how these Models were created see

The following animal species have been reported as pollinators of this plant species or its genus where their geographic ranges overlap: Bombus bifarius, Bombus centralis, Bombus flavifrons, Bombus huntii, Bombus melanopygus, Bombus sylvicola, Bombus occidentalis, and Bombus bohemicus (Macior 1974, Thorp et al. 1983, Colla and Dumesh 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 Small Onion are impacts due to non-native plant infestations and chemical herbicide application at many populations (MTNHP Threat Assessment 2021). Spotted Knapweed (Centaurea stoebe) and Cheatgrass (Bromus tectorum) are established at most populations, and some infestations are severe. Chemical herbicide application is the primary form of weed control and is likely to both damage plants and reduce habitat quality. One population is found where mining activity may also have negative impacts.

  • 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.
    • 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.
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Citation for data on this website:
Small Onion — Allium parvum.  Montana Field Guide.  .  Retrieved on , from