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Rocky Mountain Twinpod - Physaria saximontana var. dentata
Other Names:
Physaria saximontana ssp. dentata
State Rank Reason (see State Rank above)
Physaria saximontana variety dentata is presumed to be endemic to Montana, though it may occur in the adjacent mountains of Idaho and Wyoming. Plants usually occur on rocky slopes in relatively remote, montane to alpine habitats. Population counts are poorly documented, and trends are unknown. However, it is presumed that occurrences have been relatively stable or experienced only minor declines because the species' habitat is remote and largely intact. Threats have not been identified though changes in climate patterns may pose a potential risk to the state's population. Physaria saximontana var. dentata remains vulnerable to extirpation due to the species' limited range and relative rarity in Montana.
Surveys that bring forth current data on population parameters, habitat conditions, mapping, and potential threats are needed. Monitoring at a subset of populations is necessary to track population trends and assign a timely and accurate state conservation status rank.
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).
Phenology
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 Twinpod –
Physaria saximontana var.
dentata, SOC
*Pedicels are spreading to straight to curved, 5–10 mm long.
*Fruits are inflated
and obviously 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 Bladderpod –
Physaria pachyphylla, SOC
*Fruiting pedicels curve upwards (ascend), are 3-10 mm long, and less than 2 times longer than fruit.
*Fruits inflated, narrowly elliptic to globose (
not obviously appearing 2-lobed), and 3-6 mm tall. Style is 1-3 mm long, shorter than the mature fruit (silicle).
*Basal leaves have distinct petioles and blades. Basal blades are oblanceolate to orbicular in shape, nearly 1 mm thick, and cupped (
not folded).
*Plants grow on white to pinkish, limestone and gypsum soils on exposed ridges and slopes in the valley zone.
Species Range
Montana Range
Range Descriptions
Native
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: 60
(Click on the following maps and charts to see full sized version)
Relative Density
Recency
(Observations spanning multiple months or years are excluded from time charts)
Habitat
Typically found in limestone-derived talus, fellfields, and gravelly slopes at moderate to high elevations.
Ecological Communities Associated with this Species
Alpine
Alpine - Sparse and Barren
Alpine - Vegetated
Sparse and Barren
Sparse and Barren
Stewardship Responsibility
Threats or Limiting Factors
Threats to Montana's populations of Rocky Mountain Twinpod have not been reported though climate change poses a potential risk to the state's populations. The MTNHP conducted a species-level assessment using the Climate Change Vulnerability Index (CCVI) in 2021, which resulted in a Moderately Vulnerable rating to climate change. Climate change including increased ambient temperatures, decreased snowpacks, and increased frequencies and severities of drought could have negative impacts on this species; however, field-based data on the timing and magnitude are not available.
References
- 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.
MTNHP Threat Assessment. 2021. State Threat Score Assignment and Assessment of Reported Threats from 2006 to 2021 for State-listed Vascular Plants. Botany Program, Montana Natural Heritage Program, Helena, Montana.
- 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.
- Web Search Engines for Articles on "Rocky Mountain Twinpod"
