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Thick-leaf Bladderpod - Physaria pachyphylla

Species of Concern
Native Species

Global Rank: G2G3
State Rank: S2S3
(see State Rank Reason below)
State Threat Score: Low
CCVI: Moderately Vulnerable

Agency Status


External Links

State Rank Reason (see State Rank above)
See rank details.
  • Details on Status Ranking and Review
    Thick-leaf Bladderpod (Physaria pachyphylla) Conservation Status Review
    Review Date = 11/05/2012
    View State Conservation Rank Criteria
    Population Size

    Score2 - Small: Generally 2,000-10,000 individuals.

    CommentEstimated as precise population data are lacking.

    Range Extent

    Score3 - Local Endemic or Very Small Montana Range: Generally restricted to an area <10,000 sq. miles (equivalent to the combined area of Phillips and Valley Counties) or <6 Sub-basins (4th code watersheds) Range-wide OR limited to one Sub-basin in Montana

    Area of Occupancy

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

    Environmental Specificity

    Score1-2 - Moderate to High.


    ScoreNA - Rank factor not assessed.


    Score0-1 - Low to Medium.

    Intrinsic Vulnerability

    Score0-1 - Low to Moderate Vulnerability.

    Raw Conservation Status Score

    Score 8 to 11 total points scored out of a possible 16 (Rarity factors and threats only).

General Description
PLANTS: A loosely mounded perennial herb with a rosette-like growth form, 2-15 cm tall. Flowering stems are well exerted beyond the basal leaves and clothed in old leaf bases from a simple, rarely branched taproot (caudex) 4-7 mm thick. Sources: Grady and O’Kane 2007; Lesica et al. 2012.

LEAVES: Basal leaves are oblanceolate to orbicular, 15–50 mm long by 4-7 mm wide, distinct from the petioles, entire, and somewhat cupped. Stems are first decumbent and later ascend to 2–15 cm tall with alternate, spatulate-shaped leaves. The foliage takes on a pale green appearance due to the dense covering of silver-gray, 5-rayed, stellate hairs (trichomes). The leaf hairs are 0.5 mm in diameter with 5 main rays, twice bifurcate (with 16-20 terminal rays), slightly fused near the bases of the main rays, and appressed close to the leaf surface. Sources: Grady and O’Kane 2007; Lesica et al. 2012.

INFLORESCENCE: Flowers are arranged on an unbranched, elongated stalk and have curved, ascending pedicels (racemose inflorescence) which are 3-10 mm long. Flowers have 4 pale yellow sepals (3.5-4 mm), 4 separate yellow petals (6–8 mm), 6 stamens (4 long and 2 short), and 1 pistil. Fruits are silicles. Sources: Grady and O’Kane 2007; Lesica et al. 2012.

“Physa” means bladder referring to the inflated fruits in some species of this genus. “Pachy” means fat or thick, and “phylla” means leaves, referring to the stout or thick leaves of this species (Gledhill 1990).

Flowering June to July (Cross 2010; O’Kane in Flora of North America (FNA) 2010).

Diagnostic Characteristics
Montana has a rich diversity of bladderpod species totaling 17, of which 4 are endemic including Thick-leaf Bladderpod. The following Physaria species occur in Carbon County and can be distinguished from Physaria pachyphylla based on these characteristics:

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.

Sharpleaf twinpod - Physaria acutifolia
*Pedicels are spreading, straight, or sigmoid, 5-10 mm long.
*Fruits inflated and 2-lobed, 6-10 mm wide.

Double Bladderpod - Physaria brassicoides, SOC
*Pedicels are spreading, straight, or sigmoid, 5-20 mm long.
*Fruits inflated and 2-lobed, 7-10 mm wide. Replum (thin wall that separates the lobes) is narrow and constricted in the middle.

Curved Bladderpod - Physaria curvipes
*Pedicels are sigmoid to speading, 4-7 mm long.
*Fruits inflated, not 2-lobed, ovoid, and 5-9 mm tall. Style is less than half the length of the fruit (silicle).
*Basal leaf blades are thinner than 1 mm.

Wooly Twinpod - Physaria didymocarpa var. lanata, SOC
*Pedicels are spreading, straight, or sigmoid, 3-12 mm long.
*Fruits inflated and 2-lobed, 7-20 mm tall.
*Basal Leaves obovate in shape with entire to coarsely dentate margins.

Lesica’s BladderpodPhysaria lesicii, SOC
*Pedicles are recurved in an arc, 4-11 mm long. Stems and pedicles are thread-like and flexuous (filiform).
*Fruits are globose, inflated and 2-4 mm high
*Plants are less robust with thinner leaves and caudices. Plants grow at higher elevations, elative to Thick-leaf Bladderpod.

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.

Spatula-leaf Bladderpod - Physaria spatulata
*Pedicles are sigmoid-spreading, 4-12 mm long - at least twice as long as the fruit (silicle).
*Fruits inflated, not 2-lobed, ovoid, and 2-5 mm high. Style is more than half the length of the fruit.
*Basal leaf blades thinner than 1 mm.
*Plants grow in sandy or gravelly soil (calcareous or not) on exposed slopes and ridges in grasslands, steppe, woodlands, and fellfields in the plains, valleys, montane, and alpine zones.

Great Plains Bladderpod - Physaria arenosa
*Pedicles are recurved downward 5-10 mm long.
*Fruits are globose not 2-lobed, 3-5 mm high
*Basal leaves on the outside are oblong to narrowly ovate, not spatulate, and 1-5cm long with entire margins.

Silver Bladderpod - Physaria ludoviciana, SOC
*Pedicles are recurved downward 10-16 mm long.
*Fruits are globose not 2-lobed, 3-4 mm high
*Basal leaves are erect, linear, 3-7 mm long.

The genera of Physaria and Lesquerella were united under the older name of Physaria by Shehbaz and O'Kane (2002). These genera were originally separated by Rollins in his publication Cruciferae of Continental North America (1993). Rollins separated Physaria as possessing strongly didymous fruits (see Reproductive Characteristics) with deep sinuses between the valves and having fruits compressed perpendicular to the replum (Shehbaz and O'Kane 2002). Likewise, Rollins separated Lesquerella as having non-didymous fruits with shallow to no distal sinuses and having fruits compressed parallel to the replum or lacking any compression (Shehbaz and O'Kane 2002). However, the increasing amount of molecular, morphological, distributional, and ecological data do not support the distinctions put forth by Rollins (1993). Most of the members of Lesquerella now belong to the genus Physaria, except for species which possess auriculate-leaves which have been placed in the genus Paysonia (O’Kane in FNA 2010). Physaria and Lesquerella are indistinguishable in almost every morphological aspect and are monophyletic (descended from a single taxon) (Shehbaz and O'Kane 2002; O’Kane in FNA 2010). Scientific naming standards requires that the oldest name be preserved; Physaria has been recognized as a genus since 1838 while Lesquerella was established in 1888 (Shehbaz and O'Kane 2002).

Species Range
Montana Range Range Descriptions


Range Comments
Thick-leaf Bladderpod is a regional endemic species, occurring only in the Pryor Mountain Desert of south-central Montana and in the Big Horn Basin of north-central Wyoming (adjacent Carbon County, MT and Big Horn County, WY) (Lesica et al. 2012; Heidel 2016;

Thick-leaf Bladderpod was first collected by Botanist Peter Lesica in Montana in 1983, but not recognized as a new taxon until 1998 (; Grady and O'Kane 2007). Ben Grady described the new species in 1998 and along with Steve O'Kane published the findings in a 2007 paper that focused on Physaria in western North America (Grady and O'Kane 2007). A 2001 collection made in Big Horn County, Wyoming by Botanist Bonnie Heidel was later annotated by Grady and represents Wyoming's first occurrence.

As of 2020, Montana has 10 species occurrences (SOs) located between Gypsum Creek and Bighorn River. In Wyoming, Thick-leaf Bladderpod is known from 2 locations documented in 2001 and 2020.

Observations in Montana Natural Heritage Program Database
Number of Observations: 186

(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)

In Montana, Thick-leaf Bladderpod grows in dry, barren, and stony, yet edaphically diverse soils in the Pryor Mountain Desert which occur on exposed slopes, ridges, and valleys (Grady and O’Kane 2007; O’Kane in FNA 2010; and Lesica et al. 2012). The species is apparently limited to pinkish or reddish soils derived from limestone or a combination of limestone and diatomaceous earth at elevations ranging from 1,300 to 1,600 meters above sea level (Grady and O’Kane 2007; Lesica et al. 2012).

In Wyoming, it is associated with outcrops in the Chugwater Formation (Heidel 2016) which consists mainly of siltstones and shales with interspersed sandstones. The formation is brick-red in color, caused by the oxidation of iron minerals in the rock (Cavaroc and Flores 1991).
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

In Montana, Thick-leaf Bladderpod can be found growing with other mat forming perennials, though vegetation is often sparsely distributed. Associated forb and grass species include saltbush (Atriplex), buckwheat (Eriogonum), phlox (Phlox), cat’s eye (Cryptantha), vetch (Astragalus), rock goldenrod (Petradoria), needlegrass (Stipa), and wheatgrass (Elymus) (Grady and O’Kane 2007). Concomitant woody species include Limber Pine (Pinus flexilis), Utah Juniper (Juniperus osteosperma), and Curl-leaf Mountain Mohagany (Cercocarpus ledifolius) (Grady and O’Kane 2007). In Wyoming, it is associated with Rubber Rabbitbrush (Chrysothamnus nauseosus var. graveolens (syn. Ericameria nauseosus ssp. graveolens)) and Badlands Mule-ears (Wyethia scabra) (Heidel 2016).

Outcrossing pollination by insects is a required method of fertilization for successful reproduction of other Physaria species (Clark 2013; Claerbout et al. 2007). Insects, including ground-nesting bees, have been documented as pollinators for other Physaria species (Cross, P. 2010; Meier et al. 2011). No pollinators have been documented specifically for Thick-leaf Bladderpod.

Reproductive Characteristics
Plants reproduce by seed.

Perfect (contain male and female organs). Sepals are pale yellow and elliptic to oblong in shape. Petals are yellow and strap-shaped (ligulate). Pistil has a 2-celled superior ovary and a single style, 1-3 mm long.

The fruit is a silicle, 2.5-4.0 mm long. The silicle is erect, inflated, narrowly elliptic to ovoid or lance shaped, 3–6 mm high by 3-4 mm wide, and tipped with a style that at least half the length of the mature fruit. Each fruit has 8 seeds, distributed in 2 chambers (4 seeds per locule).

The Research Natural Area (RNA) program is a nationwide system created to protect a network of federally administered public lands established for the purpose of scientific research, maintaining biological diversity, and education (USFS 2014). The intent is to designate RNAs that represent the full array of North American ecosystems with their biological communities, habitats, natural phenomena, and geological and hydrological formations. These intact protected areas are managed to maintain their natural and primitive character with a minimum of human disturbance. Each RNA also serves as a baseline of ecological information that can be used to compare against other similar, yet managed ecological systems.

A type of RNA is the Area of Critical Environment Concern (ACEC). The ACEC program was established in the 1976 Federal Lands Policy and Management Act and is managed by the Bureau of Land Management (BLM) (Wikipedia Contributors 2020). Places designated as ACECs require special management to protect important historical, cultural, and scenic values, fish and wildlife, or other natural resources (BLM 2021). The BLM has extended the purpose of RNAs to that of preserving gene pools of typical and endangered plants and animals (BLM 2015; BLM 2021).

Pryor Foothill RNA/ACEC
This RNA-ACEC was established in the Approved Resource Management Plan by the MT/Dakotas BLM, Billings Field Office, recommended for approval by the MT/Dakotas BLM State Director in 2015, and is awaiting final approval by the U.S Congress (BLM 2015). The RNA-ACEC is approximately 2,606 acres in size. The management goals for the Pryor Foothills RNA/ACEC are to protect a large concentration of BLM's special status plant species and rare plant communities (unique vegetation) and to protect significant historic and cultural values in the Gyp Springs area. Large, intact populations of Thick-leaf Bladderpod live in the Pryor Foothill RNA-ACEC. A scattering of populations occur in vicinity of the Pryor Foothill RNA-ACEC. See Range Comments.

The BLM Special Status Species Policy (Manual 6840) gives the State Director the responsibilities to designate Bureau sensitive species for their respective jurisdictions and allows the list to be reviewed and updated at least every 5 years in coordination with State agencies responsible for fisheries, wildlife, and botanical resources and Natural Heritage Programs (MT/Dakotas BLM 2020). Further the State Director has the responsibility to implement procedures for the conservation of all special status species on BLM-administered lands within Montana, North Dakota, and South Dakota (MT/Dakotas BLM 2020).

Thick-leaf Bladderpod is designated as a Montana/Dakotas BLM Sensitive Species for the Billings Field Office (MT/Dakotas BLM 2020). The Montana/Dakotas BLM Sensitive status was given in part because it is a local endemic with historical and relatively current occurrences. It has been designated as Sensitive by the Montana/Dakotas BLM since 2014. The Montana/Dakotas BLM Special Status Species Policy for Sensitive plants provides guidance on field inventories and mitigation measures (MT/Dakotas BLM 2020).

Recognizing that America's rich natural heritage is of esthetic, ecological, educational, recreational, and scientific values to our Nation and its people, the Endangered Species Act (ESA) was created to recover and protect imperiled species. The ESA of 1973 as amended by Congress provides for the conservation of endangered and threatened species of fish, wildlife, and plants, and for other purposes. The ESA mostly requires the U.S. Fish and Wildlife Service (USFWS) to: a) list, classify, protect, and recover species [Sections 4, 9, and 12], b) review and evaluate federal actions for potential affects to listed species [Section 7], c) oversee recovery activities [Sections 4, 5, and 6]; d) work cooperatively with the States [Section 6] and internationally [Section 8]; and e) provide exemptions (permits) for scientific efforts and conservation activities [Section 10]. The USFWS uses five main factors to determine if a proposed species warrants listing under the ESA: 1) present or threatened habitat/range loss, 2) overutilization, 3) disease/predation, 4) inadequacy of protections, and 5) other threats. The de-listing of a species is assessed using three criteria: 1) recovery, 2) extinction, or 3) erroneous information at the time of listing. The USFWS uses a Species Status Assessment to evaluate the resiliency, redundancy, and representation to understand the current and potential future viability of a species to inform listing, consultation, and recovery decisions (USFWS 2016; USFWS Species Status Assessment).

Thick-leaf Bladderpod under the ESA
On March 11, 2021 a petition to list Thick-leaf Bladderpod and designate critical habitat under the Act was submitted to the USFWS. The 90-day Finding On A Petition to List found substantial scientific or commercial information indicating that listing as a threatened or endangered species may be warranted (USFWS 2021). Thick-leaf Bladderpod is on the USFWS's National Listing Workplan and the 12-month finding is expected to be published in 2025 (USFWS personal communication).

Threats or Limiting Factors
Across its range in Wyoming and Montana, current and potential long-term threats to Thick-leaf Bladderpod include (Montana Native Plant Society 2021):

Gypsum Mining: Gypsum is a common mineral found in the Chugwater Formation. Gypsum claims have been made on public lands in vicinity of Thick-leaf Bladderpod. Potential negative impacts from mining activities include direct removal and trampling of plants. Potential indirect negative impacts from mining activities include disturbance to habitat from soil erosion, soil compaction, and colonization by invasive species. Soils in the Chugwater Formation are known to be very susceptible to erosion.

Invasive Species: The arid landscape in which Thick-leaf Bladderpod occurs is predominately in native, intact habitat. However, Cheatgrass (Bromus tectorum) and African mustard (Malcolmia africans) are known to occur along roads that are near to thick-leaf Bladderpod populations. There is the potential for negative impacts based on the assumption that these exotics would be more competitive for soil water and nutrient resources.

Recreation: Off-road vehicle (ORVs) use commonly occurs further north in the Pryor Mountains. It is suspected that at least some ORV use could occur in vicinity of the Thick-leaf Bladderpod. Potential negative impacts from ORVs could include direct impacts to the plant from trampling and indirect impacts from soil erosion, soil compaction, and colonization of the habitat by invasive species.

Reported threats to Montana's populations of Thick-leaf Bladderpod include potential consequences from proposed oil and gas exploration and expansion of non-native plant populations (MTNHP Threat Assessment 2021). Road construction and drill site activity proposed in the Pryor Foothill RNA would create ground disturbance in an area where soils are prone to rapid erosion. Indirectly, this ground disturbance could remove biotic soil crusts, which contribute to the stability of surface soils, and requires years or decades recover. Nearby non-native plants may outcompete Thick-leaf Bladderpod and have a strong potential to increase where ground disturbance exposes bare soil. An overall State Threat Score of "low" is assigned because these potential threats have not been realized or documented as occurring (MTNHP Threat Assessment 2021).

  • Literature Cited AboveLegend:   View Online Publication
    • Al-Shahbaz, I.A. and S.L. O'Kane. 2002. Lesquerella is united with Physaria (Brassicaceae). Novon 12:319-329.
    • BLM Billings Field Office. 2015. Approved Resource Management Plan Appendices. Billings, MT: U.S. Department of the Interior Bureau of Land Management. 438 p.
    • Cavaroc, V.V. and R.M. Flores. 1991. Red beds of the Triassic Chugwater Group, Southwestern Powder River Basin, Wyoming. pp. E1-!17. IN: V.F. Nuccio, P.L. Hansley, W.A. Cobban, and C.G. Whitney, Evolution of Sedimentary Basins: Powder River Basin. Denver, CO: U.S. Geological Survey Bulletin, 1917-E.
    • Claerbout, A.E., J.M. Coons, H.R. Owen, and K.R. Robertson. 2007. Floral Biology of Physaria ludoviciana (Brassicaceae), a Plant Rare to the Midwest. Castanea 72(3):130-137.
    • Clark, S.L. 2013. Reproductive biology and impacts of energy development on Physaria congesta and Physaria obcordata (Brassicaceae), two rare and threatened plants in the Piceance Basin, Colorado. M.Sc. Thesis. Logan, UT: Utah State University. 90 p.
    • Cross, P. 2010. Bladderpod: A study in diversity. Kelseya 23(4):8-9.
    • 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.
    • Gledhill, D. 1990. The names of plants. 2nd Ed. New York, NY: Cambridge University Press. 426 p.
    • Grady, B. R., and S. L. O'Kane. 2007. New Species and Combinations in Physaria (Brassicaceae) from Western North America. Novon 17 (2): 182-192.
    • Heidel, B. 2016. Noteworthy collection. Madrono 63(1):7.
    • Lesica, P., M.T. Lavin, and P.F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
    • Meier, R., M. Joseph, M. Arduser, and E. Westhus. 2011. The pollination biology of an annual endemic herb, Physaria filiformis (Brassicaceae), in the Missouri Ozarks following controlled burns. Journal of the Torrey Botanical Society 138(3):287-297.
    • Montana Native Plant Society (MNPS). 2021. Vascular Plant SOC/PSOC Threat Assessment and Ranking. Threat rank assignments and data compilation from 2018 to 2021 by the Interagency Plant Threat Ranking Committee. Data housed at the Montana Natural Heritage Program, Helena, Montana.
    • MT/Dakotas BLM. 2020. 2020 Montana/Dakotas Special Status Species List. Instruction Memorandum No. MT-2020-012. March 16th. Montana/Dakotas State Office, 2001 Southgate Drive, Billings, Montana.
    • 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.
    • U.S Fish and Wildlife Service (USFWS). 2016. USFWS Species Assessment Framework: An Integrated Analytical Framework for Conservation. August. Version 3.4.
    • U.S. Fish and Wildlife Service. 2021. 90-Day Finding Petition Review Form for Physaria pachyphylla. Federal Docket Number: FWS-R6-ES-2021-0117. Washington D.C.
    • USDA Forest Service. 2014. Research Natural Areas. Accessed 4 February 2021.
    • USDI Bureau of Land Management. 1996. Special status species management. BLM Manual Supplement 6840 of 8 April 1996. Billings, MT.
    • USDI Bureau of Land Management. 2021. Areas of critical environmental concern. Accessed January 28, 2021.
    • Wikipedia contributors. 2020. Area of critical environmental concern. Wikipedia, The Free Encyclopedia. Accessed 27 January 2021.
  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Grady, Benjamin R. 2005. Molecules, morphology, and biogeography: an analysis of the phylogeny and taxonomy of the Physaria reediana species complex (Brassicaceae).
    • 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.
    • Shepard, E. 2005. BLM Land Use Planning Handbook H-1601-1. Grand Junction, CO: U.S. Department of the Interior Bureau of Land Management. 161 p.
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