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Montana Field Guides

Wyoming Tansymustard - Descurainia torulosa

Species of Concern
Native Species

Global Rank: G2
State Rank: S1
(see State Rank Reason below)
State Threat Score: High - Medium

Agency Status


External Links

State Rank Reason (see State Rank above)
One collection from Park County, Montana (Consortium of Pacific Northwest Herbaria;
  • Details on Status Ranking and Review
    Wyoming Tansymustard (Descurainia torulosa) Conservation Status Review
    Review Date = 08/25/2016
    View State Conservation Rank Criteria
    Population Size

    ScoreA - 1 - 50 individuals

    Range Extent

    ScoreA - <100 sq km (< ~40 sq mi)

    Area of Occupancy

    ScoreA - 1 4-km2 grid cell

    Number of Populations

    ScoreA - 1 - 5

    Number of Occurrences or Percent Area with Good Viability / Ecological Integrity

    ScoreB - Very few (1-3) occurrences with excellent or good viability or ecological integrity

    Environmental Specificity

    ScoreC - Moderate. Generalist or community with some key requirements scarce

    Long-term Trend

    ScoreU - Unknown


    ScoreU - Unknown


    ScoreU - Unknown

    CommentThreats: Unknown/undetermined.

    Intrinsic Vulnerability

    ScoreU - Unknown

General Description
PLANTS: Short-lived perennials, somewhat to densely hairy all over. Stems few to many, arising from the base, generally not branched below and very seldom branched above, decumbent (Goodson and Al-Shehbaz in FNA 2010), 4–15 cm. Vestiture of stellate hairs (Lesica 2012).

LEAVES: Basal leaves: rosulate; petiole 3-14 mm; blade oblanceolate, 9-35 mm in length, the 3-5 pairs of blade lobes oblong to oblanceolate with smooth margins (FNA 2010). Stem leaves lacking petiole or short-petiolate; blades reduced distally (FNA 2010), 2–10 cm in length, oblanceolate, pinnate, the pinnae lobed to entire (Lesica 2012).

INFLORESCENCE: Racemes, growing significantly longer in fruit (Goodson and Al-Shehbaz in FNA 2010).

Flowers June-July (FNA 2010).

Diagnostic Characteristics
Descurainia torulosa has clearly distally-curved fruits, is slightly pubescent and strongly torulose. Its stems (often several) are decumbent and unbranched.

The fruit of the similar Descuraina incana is straight, glabrous, and barely or not at all torulose. Its simple stems are erect and branched (Goodson and Al-Shehbaz in FNA 2010).

Species Range
Montana Range Range Descriptions


Range Comments
Endemic to western Wyoming and Park County, Montana.

Observations in Montana Natural Heritage Program Database
Number of Observations: 1

(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)

Talus slopes in the subalpine zone within Montana (Lesica et al. 2012).
Predicted Suitable Habitat Model

This species has a Predicted Suitable Habitat Model available.

To learn how these Models were created see

Reproductive Characteristics
Flowers: Sepals upright, somewhat yellow, hairy (Goodson and Al-Shehbaz in FNA 2010); petals yellow, 1–2 mm in length (Lesica 2012).

Fruit: Fruit clearly curved distally, slightly pubescent, erect or nearly (Goodson and Al-Shehbaz in FNA 2010), torulose (with bulges around and constrictions between the seeds), 6–15 mm in length, up to 1 mm in width, tapering at both ends; style 0.1–0.3 mm in length. Seeds 10 to 18 per locule in 1 row (Lesica 2012), reddish brown; pedicels upright or nearly so, straight, 1.5-3 mm in length (Goodson and Al-Shehbaz in FNA 2010).

Threats or Limiting Factors
Reported threats to Montana’s only population of Wyoming Tansymustard are due to invasive species (MTNHP Threat Assessment 2021). Direct competition and declining habitat quality are reported to have moderate to serious negative impacts.

  • Literature Cited AboveLegend:   View Online Publication
    • Flora of North America Editorial Committee, eds. 2010. Flora of North America North of Mexico. Volume 7. Magnoliophyta: Salicaceae to Brassicaceae. Oxford University Press, Inc., NY. 832 pp.
    • Lesica, P., M.T. Lavin, and P.F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
  • 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.
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Citation for data on this website:
Wyoming Tansymustard — Descurainia torulosa.  Montana Field Guide.  .  Retrieved on , from