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Montana Field Guides

Rocky Mountain Twinpod - Physaria saximontana var. dentata

Species of Concern
Native Species

Global Rank: G3T3
State Rank: S3
(see State Rank Reason below)
State Threat Score: No Known Threats
CCVI: Moderately Vulnerable

Agency Status


External Links

State Rank Reason (see State Rank above)
State endemic known from several counties across central and southern Montana mountain ranges.
  • Details on Status Ranking and Review
    Rocky Mountain Twinpod (Physaria saximontana var. dentata) Conservation Status Review
    Review Date = 08/22/2012
    View State Conservation Rank Criteria
    Population Size

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

    CommentPopulation size likely >10,000 individuals though precise population data are lacking.

    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 as the species often occurs in remote, rocking habitats.


    Score0-1 - Low to Medium.

    Intrinsic Vulnerability

    Score0-1 - Low to Moderate Vulnerability.

    Raw Conservation Status Score

    Score 5 to 8 total points scored out of a possible 19.

General Description
Stems ascending to prostrate, 3–10 cm from a simple caudex clothed in old leaf bases. Basal leaves 15–40 mm long; the blades orbicular to rhombic, deeply few-toothed or lyrate. Stem leaves oblanceolate to spatulate, entire. Vestiture of dense, stellate hairs with branched stellae. Petals 8–12 mm long. Fruit of 2 ovate lobes, inflated, 7–11 mm high, the apical sinus deep, the basal sinus absent; style 5–7 mm long; seeds 2 per locule; pedicels spreading, straight to curved, 5–10 mm long. Our plants are subspecies dentata (Rollins) O'Kane (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Flowering and fruiting in June and July with fruits maturing into August.

Diagnostic Characteristics
Only variety dentata occurs in Montana. Variety saximontana, which is only known from Wyoming, can be distinguished by its entire basal/rosette leaves and longer styles (3 or more times the length of the replum) vs. the toothed apical margins of the basal/rosette leaves of variety dentata and the shorter styles (1-2 times or less the length of the replum). Another species occurring in southwest Montana is P. didymocarpa, which differs in having deep sinuses at both the top and bottom of the fruit. The fruit of P. saximontana is notched with only a sinus at the top.

Rocky Mountain TwinpodPhysaria saximontana var. dentata, SOC
*Pedicels are spreading to straight to curved, 5–10 mm long.
*Fruits are inflated and 2-lobed, 7-11 mm high.
*Basal leaf blades are orbicular to rhombic in shape, 15–40 mm long, and deeply few-toothed or lyrate.
*Plants typically grow in limestone-derived soils of grasslands and fellfields on exposed slopes in the montane zone.

Thick-leaf BladderpodPhysaria pachyphylla, SOC
*Pedicels curve upwards (ascend), 3-10 mm long.
*Fruits inflated, not 2-lobed, and narrowly elliptic to ovoid, 3-6 mm tall. Style is more than half the length of the fruit (silicle).
*Basal leaves have distinct petioles and blades. Blades are spatulate to oblanceolate in shape, nearly 1 mm thick and cupped (but not folded), and with entire margins [key characteristic].
*Plants grow on pinkish or reddish soils derived from limestone on exposed slopes and ridges in valleys.

Species Range
Montana Range Range Descriptions


Range Comments
Montana endemic. Scattered across several counties in the central and western parts of the state.

Observations in Montana Natural Heritage Program Database
Number of Observations: 44

(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)

Typically found in limestone-derived talus, fellfields, and gravelly slopes at moderate to high elevations.
Predicted Suitable Habitat Model

This species has a Predicted Suitable Habitat Model available.

To learn how these Models were created see

Ecological Systems Associated with this Species

Threats or Limiting Factors
Threat impact not assigned because threats are not known (MTNHP Threat Assessment 2021).

  • Literature Cited AboveLegend:   View Online Publication
    • 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.
    • Mincemoyer, S. 2005. Surveys of significant plant resources and related vegetation types for the Butte Office of the Bureau of Land Management. Montana Natural Heritage Program, Helena, MT. 11 pp + appendices.
    • Rollins, R. C. 1984. Studies in the Cruciferae of western North America II. Contributions Gray Herbarium 214:1-18.
    • Rollins, R. C. 1993. The Cruciferae of Continental North America: systematics of the mustard family from the Arctic to Panama. Stanford University Press, Stanford, California. 976 pp.
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Citation for data on this website:
Rocky Mountain Twinpod — Physaria saximontana var. dentata.  Montana Field Guide.  .  Retrieved on , from