Montana Field Guide

PLANTS: A perennial, silvery pale-green forb with a strong basal rosette of leaves, and decumbent to ascending stems of 2-15 cm tall that usually arise from an unbranched taproot (caudex), 4-7 mm thick. Flowering stems are often well exerted beyond the basal leaves and clothed in old leaf bases. Sources: Grady and O’Kane 2007; Lesica et al. 2022.

LEAVES: Basal leaves are leathery, oblanceolate to orbicular in shape, somewhat cupped, have smooth (entire) margins, and 15–50 mm long, 4-7 mm wide, and often 1 mm thick. Petioles are distinct from the blades. Stems are initially decumbent and later ascend. Stem leaves are alternately arranged and spatulate-shaped. The foliage takes on a pale green appearance due to the dense covering of silver-gray, stellate hairs (trichomes). 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. 2022.

INFLORESCENCE: A raceme of pale yellow flowers, arranged in unbranched, elongated stalks, with curved, ascending pedicels of 3-10 mm long. Sepals are 4, yellow, and pale, 3.5-4 mm long. Petals are 4, yellow, and 6–8 mm long. Stamens are 6 (4 long and 2 short). Pistil is singular. Fruits are a slightly ovoid silicle. Sources: Grady and O’Kane 2007; Lesica et al. 2022.

TAXONOMY & NOMENCLATURE
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 Flora of North America (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).

Physaria pachyphylla was recognized as a novel taxon in 1998, and formally described as a species new to science in 2007 by Ben Grady and Steve O'Kane.

“Physa” is Greek for 'bladder' which is in reference to the inflated fruits in some species of Physaria (O'Kane in FNA 2010). The common name of Thick-leaf Bladderpod was published by Grady and O'Kane (2007). “Pachy” means fat or thick, and “phylla” means leaves, referring to the stout or thick leaves of this species (Gledhill 1990).

Generally, flowering from June to July (Cross 2010; O’Kane in Flora of North America (FNA) 2010). However, earlier dates are also expected and dependent upon local climate conditions.

Montana has a rich diversity of 17 bladderpod species that inlcudes 4 endemic species. A technical key and mature fruits are necessary to distinguish Physaria species. The following species occur in Carbon County and can be distinguished from Physaria pachyphylla based on a suite of characteristics found in a given population:

Thick-leaf Bladderpod – Physaria pachyphylla, SOC
*Inflorescence is a subumbellate raceme.
*Flower pedicels curve upwards (ascend), 3-10 mm long, and less than 2 times longer than fruit.
*Fruits inflated, 1-lobed (not 2-lobed), and narrowly elliptic to globose, 3-6 mm tall. Style is 1-3 mm long, shorter than the mature 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 white to pinkish, limestone and gypsum soils on exposed ridges and slopes in the valley zone.

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 Bladderpod – Physaria 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 Twinpod – Physaria 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.

Thick-leaf Bladderpod grows on stony, calcareous (limestone or gypsum) soils on exposed slopes and ridges in the valley zones in Carbon County, Montana (Lesica 2022). The calcareous parent material is derived from limestone or a combination of limestone and diatomaceous earth and is generally comprised of silt-sized particles, which breaks down to its finest texture or to coarse gravel (Grady and O'Kane 2007; Pipp, Heidel, and Herman 2025). In Montana and Wyoming, plants have been found in the Chugwater Formation and Gypsum Spring Formation (also called Piper Formation in Montana) (Pipp, Heidel, and Herman 2025). Plants have been found where surface soils vary in color from white to pinkish but are not red to dark red. Plants grow in exposed settings, often situated on prominent landforms such as ridge tops and rims, butte shoulders, and rocky escarpment breaks, and also at the base of slopes and on low mounds in valleys or open terrain (Pipp, Heidel, and Herman 2025). Across its global range, plants have been found at elevations ranging from 4,150 to 5,680 feet (1,265 to 1,732 meters) above sea level (Pipp, Heidel, and Herman 2025).

ASSOCIATED SPECIES
In Montana and Wyoming, Thick-leaf Bladderpod occupies sparsely vegetated habitat with mainly low-growing perennial forbs and bunchgrasses (Grady and O'Kane 2007; Pipp, Heidel, and Herman 2025). Associated plant species are either consistently or occasionally present. Consistently common forb and grass associates included: Hooker's Sandwort (Arenaria hookeri), Fourwing Saltbush (Atriplex canescens), Mountain Cat’s eye (Cryptantha cana), Parasol Buckwheat (Eriogonum brevicaule var. canum), Stemless Four-nerve Daisy (Hymenoxys acaulis), Richardson's Bitterweed (Hymenoxys richardsonii), Spiny and Moss Phlox (Phlox hoodii and P. muscoides, respectively), Stemless Mock Goldenweed (Stenotus acaulis), Rayless Tansy-aster (Xanthisma grindelioides, Bluebunch Wheatgrass (Elymus spicatus), and Purple Three-Awn Grass (Aristida purpurea var. fendleriana). In the foothills, Utah Juniper (Juniperus osteosperma) was often present.

POLLINATORS
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 2010; Meier et al. 2011). No pollinators have been documented specifically for Thick-leaf Bladderpod.

Plants reproduce by seed.

FLOWERS
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-chambered superior ovary and a single style, 1-3 mm long.

FRUITS
The fruit is a silicle. Silicle is erect, globose or ellipsoid, slightly inflated with a slight apical constriction (slight latispetate compression), densely pubescent with closely-appressed hairs (trichomes), and 3-6 mm tall. Style is shorter than mature fruit, (2.5)1-3(4) mm long. Silicle appears 1-lobed, but is composed of two valves or chambers. Each fruit has 8 seeds, distributed in 2 chambers (4 ovules per locule).

RESEARCH NATURAL AREAS and AREA OF CRITICAL ENVIRONMENTAL CONCERN PROGRAM
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 Foothills RNA/ACEC – East Pryor Mountain ACEC
The Pryor Foothills RNA/ACEC has management goals to protect unique vegetation and significant historic and cultural values. The East Pryor Mountain ACEC has management goals to protect special status plant species, wild horse and wildlife habitat, historical/cultural resources, and paleontological values. Intact populations of Thick-leaf Bladderpod live in porions of the Pryor Foothill RNA-ACEC and East Pryor Mountain ACEC. These RNAs/ACECs were established in the Approved Resource Management Plan by the Montana/Dakotas BLM (MT/Dakotas BLM), Billings Field Office in 2015 (BLM 2015). Both RNAs/ACECs were recommended by the MT/Dakotas BLM State Director for withdrawal from all locatable mineral entry, which if approved would apply to new claim applicants, and other stipulations (BLM 2015). However, recommendations listed in the 2015 Billings Field Office - Approved Resource Management Plan are still awaiting final approval by the U.S Congress (BLM 2015).

BLM SPECIAL STATUS SPECIES
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).

ENDANGERED SPECIES ACT
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 found substantial scientific or commercial information indicating that listing as a threatened or endangered species may be warranted (USFWS 2021). In 2023 Thick-leaf Bladderpod was put onto the National Listing Workplan. In 2024, the USFWS initiated both a 12-month review and a Species Status Assessment (SSA). The USFWS anticipates making a listing-determination in 2026.

Across its range in Wyoming and Montana, the following threats have been identified as factors that can, if not properly mitigated or managed, contribute to putting Thickleaf-Bladderpop populations at risk of state extirpation in Montana or global extinction (Montana Native Plant Society 2021; Pipp, Heidel, and Herman 2025):

Mining and Quarrying
Thick-leaf Bladderpod populations occur on soils that can or have been mined for gypsum, uranium, gravel, and other earth materials. Potential negative direct impacts include direct removal and trampling of plants and ground-disturbance. Potential indirect negative impacts come from ground-disturbing activities that alter the biological soil crust layer and expand non-native plant species. Ground-disturbing activities can result in soil erosion, soil compaction, destroying the biological soil crust layer, and other soil and water property changes that are necessary for the viability of Thick-leaf Bladderpod populations. Soils in the Chugwater, Gypsum Spring, or Piper Formations are known to be very susceptible to erosion.

Without appropriate mitigation, the potential for ground-disturbance to known Thick-lead Bladderpod populations come from proposed mining activities for gypsum exploration, to safe-guard abandoned defense-related uranium mines (DRUM), and possible quarrying for limestone (Pipp, Heidel, and Herman 2025). Safe-guarding DRUM sites is done to reduce radiation exposure to people and wildlife, and typically involves some access road reconstruction; installing polyurethane foam, cable nets, or bat gates across adits and shafts; or back-filling features with local materials.

Non-native Plant 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) plants are found within and along the road systems for at least three Thick-leaf Bladderpod occurrences. Cheatgrass and African Mustard lack population controls and can outcompete native plants for soil water and nutrients. In addition, the establishment of Cheatgrass can alter the ecology and fire cycle of a site (Peters and Bunting 1994; Weber, Budel, and Belnap (eds.) 2016).

Recreation
Off-road vehicle (ORVs) use can directly trample Thick-leaf Bladderpod, resulting in death or damage. Potential indirect impacts from ORVs can create soil erosion and compaction, alter the soil's microtopography, and provide vectors for non-native plant establishment. Unauthorized ORV use has been observed at one occurrence, and is being addressed by the MT/Dakotas BLM.

Lack of Federal Protection
Portions of the Pryor Foothills RNA/ACEC and East Pryor Mountains ACEC contain intact, viable populations of Thick-leaf Bladderpod. The MT/Dakotas BLM, Approved Resource Management Plan for the Billings Field Office recommended a withdrawal from mineral entry and all locatable minerals along with other stipulations (MT/Dakotas BLM 2015). The formal approval of these recommendations would help protect the plants within these ACECs from mining activities proposed by new claim applications The change in management recommendations put forth by the MT/Dakotas BLM requires formal approval by the U.S. Congress or the Secretary of Interior. As of 2025, formal approval has not been granted. The lack of formally approving the recommendations contributes to potentially making Thick-leaf Bladderpod plants more vulnerable to loss.

STATE THREAT SCORE REASON
Reported threats to Montana's populations of Thick-leaf Bladderpod include potential negative consequences from proposed mining, quarrying, and related mining activities, non-native plant populations, unauthorized off-road vehicle use, and a lack of federal protections at specific ACECs (MTNHP Threat Assessment 2025). An overall State Threat Score of "High to Medium" is assigned because proposed actions have the potential to harm, especially without appropriate mitigation, at least some Thick-leaf Bladderpod occurrences in Montana.