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Montana Field Guides

Wyoming Thistle - Cirsium pulcherrimum

Species of Concern
Native Species

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

Agency Status


External Links

State Rank Reason (see State Rank above)
Known in Montana from one badlands area of Powder River County with a small number of scattered individuals observed in 2006. Also, reported for Dawson and Garfield Counties by Flora of the Great Plains and 1 collection from each of Carbon and Custer Counties.
  • Details on Status Ranking and Review
    Wyoming Thistle (Cirsium pulcherrimum) Conservation Status Review
    Review Date = 06/06/2012
    View State Conservation Rank Criteria
    Population Size

    Score2-3 - Very Small to Small: Population size is imprecisely known but is believed to be <10,000 individuals.

    CommentPopulation levels are poorly documented, though appear to be relatively small based upon available collection data.

    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

    Score2 - Low: Generally occurring in 4-10 Subwatersheds (6th Code HUC’s).

    CommentA few additional collections are known beyond location data currently in the MTNHP database.

    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:

    CommentLikely relatively stable.


    Score0-2 - Low to High Threat Levels.

    CommentPotential threats are undocumented, though are likely to be relatively minor in scope or immediacy based upon available distribution information and related data. The introduced Rhinocyllus weevil may eventually pose a threat to this species.

    Intrinsic Vulnerability

    Score0-1 - Low to Moderate Vulnerability.

    Raw Conservation Status Score

    Score 6 to 11 total points scored out of a possible 19.

General Description
Taprooted perennial with 1-few erect or ascending stems that are arachnoid-tomentose or sometimes glabrate. Flowers are pink to purple, 18-25 mm long, tubes 7-9 mm, throats 5.5-7.5 mm, lobes 4-8 mm; style tips 3-5.5 mm. The 1 to several heads are borne singly or in 2-3-headed clusters at the tips of the main stem and branches in an open, congested, or flat-topped fashion, heads sometimes also in present in distal axils. Peduncles 0-15 cm. Leaf blades are linear to oblong, oblanceolate, or elliptic, 5-25 × 0.6-7 cm, unlobed and merely spinulose or spiny-dentate to regularly pinnatifid, typically with 5-8 pairs of lobes, well separated, and usually with broad, U-shaped sinuses to crowded, linear to triangular-ovate, ascending-spreading to retrorse, merely spinulose to coarsely dentate or few lobed, primary spines are slender, 2-7 mm long. Lower leaf surfaces are usually densely arachnoid-tomentose, while upper surfaces are typically green, glabrous or less commonly thinly to densely gray-tomentose; basal leaves often present at flowering, spiny winged-petiolate; principal cauline well distributed along stem, gradually reduced upwards, lower leaves usually winged-petiolate, while mid and upper leaves typically are sessile, leaves decurrent along stem for 1.5-3.5 cm.
Involucres are ovoid to campanulate, 1.8-2.7 × 1-2 cm, thinly arachnoid-tomentose or glabrate. Bracts are in 6-7 series, ± imbricate, green or with a dark subapical patch or appendage, linear to linear-lanceolate, margins entire, abaxial faces with narrow glutinous ridge; outer and middle bases appressed, apical appendages spreading to stiffly ascending, linear-lanceolate to acicular, entire, spines spreading or ascending, stout, 2-7 mm, often flattened; apices of inner stiffly erect or sometimes flexuous, narrow, flat. Pappus is 14-16 mm long. (adapted from FNA treatment vol 19).

Flowering in June-July.

Diagnostic Characteristics
Similar species include Cirsium canescens and C. flodmanii both of which occur in eastern Montana. The former can usually be distinguished by having the upper leaf surfaces being slightly tomentose and by the leaf lobes being over 3.5 times as long as wide. The latter species usually has stem leaves that only clasp the stem or are short-decurrent compared to the typically, long-decurrent leaves (middle leaves with wings usually >15 mm long) of C. pulcherrimum. A technical manual should be consulted for positive identification.

Species Range
Montana Range Range Descriptions


Range Comments
Eastern Montana, south to Wyoming, n Colorado, ne Utah, nw Nebraska and west to se Idaho.

Observations in Montana Natural Heritage Program Database
Number of Observations: 19

(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)

Sparsely-vegetated soils of washes and steep, eroded gullies in dissected or badlands topography. Associated species include Juniperus scopulorum, Chrysothamnus nauseosus, Artemisia ludoviciana, Atriplex confertifolia and Elymus trachycaulis. In other areas, this species is listed as typically growing in rocky or stony soils. However, in our area the species has also been noted from fine-textured soils.
Predicted Suitable Habitat Model

This species has a Predicted Suitable Habitat Model available.

To learn how these Models were created see

The effects, if any of the introduced Rhinocyllus weavil on this species are unknown. Additional information on this species' ecology and management in Montana are lacking at this time.

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 frigidus, Bombus huntii, Bombus mixtus, Bombus nevadensis, Bombus rufocinctus, Bombus sylvicola, Bombus ternarius, Bombus terricola, Bombus sitkensis, Bombus occidentalis, Bombus pensylvanicus, Bombus bimaculatus, Bombus griseocollis, Bombus impatiens, Bombus insularis, Bombus suckleyi, Bombus bohemicus, and Bombus flavidus (Thorp et al. 1983, Mayer et al. 2000, Wilson et al. 2010, Colla and Dumesh 2010, Colla et al. 2011, Koch et al. 2012, Williams et al. 2014, Tripoldi and Szalanski 2015).

Threats or Limiting Factors
Reported threats to Montana's populations of Wyoming Thistle indicate impacts at one population due to chemical herbicide application (MTNHP Threat Assessment 2021). Wyoming Thistle has a stature similar to non-native thistle species, and it is occasionally targeted by chemical weed control applicators in error.

  • Literature Cited AboveLegend:   View Online Publication
    • Colla, S., L. Richardson, and P. Williams. 2011. Bumble bees of the eastern United States. Washington, DC: USDA Forest Service, Pollinator Partnership. 103 p.
    • 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.
    • 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.
    • 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.
    • Tripoldi, A.D. and A.L. Szalanski. 2015. The bumble bees (Hymenoptera: Apidae: Bombus) of Arkansas, fifty years later. Journal of Melittology 50: doi:
    • 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. 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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Citation for data on this website:
Wyoming Thistle — Cirsium pulcherrimum.  Montana Field Guide.  .  Retrieved on , from