Roadless Areas
Home/Species/ Payson's Milkvetch

Astragalus paysonii

(Rydb.) Barneby

Payson's Milkvetch

G3Vulnerable Found in 4 roadless areas NatureServe Explorer →
G3VulnerableGlobal Rank
MediumThreat Impact
Identity
Unique IDELEMENT_GLOBAL.2.130516
Element CodePDFAB0F6P0
Record TypeSPECIES
ClassificationSpecies
Classification StatusStandard
Name CategoryVascular Plant
Endemicendemic to a single nation
KingdomPlantae
PhylumAnthophyta
ClassDicotyledoneae
OrderFabales
FamilyFabaceae
GenusAstragalus
Concept Reference
Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.
Conservation Status
Rank Method Rank calculation - Biotics v2
Review Date2025-04-18
Change Date1995-05-30
Edition Date2025-04-18
Edition AuthorsStoner, N. (1993), rev. Johnson, J. (2025)
Threat ImpactMedium
Range Extent20,000-200,000 square km (about 8000-80,000 square miles)
Number of Occurrences21 - 80
Rank Reasons
Astragalus paysonii is a perennial herb that is found in the western United States in western Wyoming and central Idaho. Despite its limited distribution, occurrences are moderately abundant and some occupy large areas. Due to its preference for disturbed habitats, threats to the species are not well understood.
Range Extent Comments
Astragalus paysonii has a limited, split distribution with one group of occurrences in western Wyoming and another in central Idaho (FNA 2023, BONAP 2015). Range extent was estimated using herbarium specimens, photo-based observations, and NatureServe Network occurrence data collected between 1994 and 2025 (GBIF 2025, iNaturalist 2025, NatureServe 2025, RARECAT 2025, SEINet 2025, CPNWH 2025).
Occurrences Comments
By applying a 1 km separation distance to herbarium specimens, photo-based observations, and NatureServe Network occurrence data documented between 1994 and 2025, it is estimated that there are 76 occurrences rangewide (GBIF 2025, iNaturalist 2025, NatureServe 2025, RARECAT 2025, SEINet 2025, CPNWH 2025).
Threat Impact Comments
Astragalus paysonii is known to prefer open, disturbed sites such as fire scars, clearcuts, utility corridors, and road shoulders (FNA 2023). This species colonizes disturbed areas and gradually declines as competition increases (Heidel 2013). Road maintenance, including mowing and grading, may maintain suitable habitat for this species, but major construction and earth-moving may cause the extirpation of occupied sites (Heidel 2013). Invasive weeds and efforts to control them, may limit the available habitat for this species in disturbed areas.
Ecology & Habitat

Habitat

Astragalus paysonii grows in open aspen, lodgepole pine, and Douglas-fir forests, burned-over or clear-cut forests, roadcuts, and other disturbed areas on decomposed granite (FNA 2023).
Terrestrial Habitats
Forest/WoodlandForest Edge
Other Nations (1)
United StatesN3
ProvinceRankNative
IdahoS3Yes
WyomingS2Yes
Threat Assessments
ThreatScopeSeverityTiming
4 - Transportation & service corridorsLarge (31-70%)Neutral or Potential BenefitHigh (continuing)
4.1 - Roads & railroadsRestricted (11-30%)Neutral or Potential BenefitHigh (continuing)
4.2 - Utility & service linesRestricted (11-30%)Neutral or Potential BenefitHigh (continuing)
5 - Biological resource useLarge (31-70%)Neutral or Potential BenefitModerate (short-term)
5.3 - Logging & wood harvestingLarge (31-70%)Neutral or Potential BenefitModerate (short-term)
5.3.4 - Unintentional effects: large scale (species being assessed is not the target) [harvest]Large (31-70%)Neutral or Potential BenefitModerate (short-term)
7 - Natural system modificationsLarge (31-70%)Moderate or 11-30% pop. declineModerate (short-term)
7.1 - Fire & fire suppressionLarge (31-70%)Moderate or 11-30% pop. declineModerate (short-term)
7.1.2 - Suppression in fire frequency/intensityLarge (31-70%)Moderate or 11-30% pop. declineModerate (short-term)
8 - Invasive & other problematic species, genes & diseases———
8.1 - Invasive non-native/alien species/diseases———

—

Plant Characteristics
DurationPERENNIAL
Economic Value (Genus)Yes
Roadless Areas (4)
Idaho (1)
AreaForestAcres
West Meadow CreekNez Perce-Clearwater National Forest115,949
Wyoming (3)
AreaForestAcres
Grayback RidgeBridger-Teton National Forest295,113
Salt River RangeBridger-Teton National Forest235,661
South Wyoming RangeBridger-Teton National Forest85,776
References (12)
  1. Baumann, Katie, Plant Biologist, Salmon-Challis National Forest. 2025. Emails regarding the status and trends of certain rare plant species on the Salmon-Challis National Forest.
  2. Consortium of Pacific Northwest Herbaria (CPNWH). 2025. Online database of vascular plant specimens from the Pacific Northwest. Online. Available: http://www.pnwherbaria.org/index.php (accessed 2025).
  3. Daines, M. 2025. Comments on rank updates for USFS project.
  4. Flora of North America Editorial Committee (FNA). 2023. Flora of North America north of Mexico. Vol. 11. Magnoliophyta: Fabaceae, parts 1+2. Oxford Univ. Press, New York. xxvii + 1108 pp.
  5. Global Biodiversity Information Facility (GBIF). 2025. Global Biodiversity Information Facility (GBIF) data portal. Online. Available: https://www.gbif.org/ (accessed 2025).
  6. iNaturalist. 2025. Online. Available: https://www.inaturalist.org (accessed 2025).
  7. Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.
  8. NatureServe. 2025. NatureServe Network Biodiversity Location Data. NatureServe, Arlington, Virginia.
  9. NatureServe's Rapid Analysis of Rarity and Endangerment Conservation Assessment Tool (RARECAT). 2024. Version: 1.1.1 (released Oct 01, 2024).
  10. Southwest Environmental Information Network (SEINet). 2025. Collections Databases. Online. Available: https://swbiodiversity.org/seinet/collections/index.php (accessed 2025).
  11. Spahr, R., L. Armstrong, D. Atwood, and M. Rath. 1991. Threatened, endangered, and sensitive species of the Intermountain Region. U.S. Forest Service, Intermountain Region, Ogden, UT.
  12. The Biota of North America Program (BONAP). 2015. Taxonomic Data Center. (http://www.bonap.net/tdc). Chapel Hill, N.C. [maps generated from Kartesz, J.T. 2015. Floristic Synthesis of North America, Version 1.0. Biota of North America Program (BONAP). (in press)]