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Astragalus arthurii

M.E. Jones

Arthur's Milkvetch

G3Vulnerable Found in 5 roadless areas NatureServe Explorer →
G3VulnerableGlobal Rank
MediumThreat Impact
Identity
Unique IDELEMENT_GLOBAL.2.151286
Element CodePDFAB0F0W0
Record TypeSPECIES
ClassificationSpecies
Classification StatusStandard
Name CategoryVascular Plant
Endemicendemic to a single nation
KingdomPlantae
PhylumAnthophyta
ClassDicotyledoneae
OrderFabales
FamilyFabaceae
GenusAstragalus
Synonyms
Astragalus arthuriM.E. Jones
Other Common Names
Waha Milkvetch (EN) waha milkvetch (EN)
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 Date2025-03-25
Change Date2025-03-25
Edition Date2025-03-25
Edition AuthorsJohnson, J. (2025)
Threat ImpactMedium
Range Extent5000-20,000 square km (about 2000-8000 square miles)
Number of Occurrences21 - 80
Rank Reasons
Astragalus arthurii is a perennial herb native to northeastern Oregon, southeastern Washington, and western Idaho, USA. With a limited range, moderate threats from grazing and invasive species, and unknown population trends, this species is vulnerable.
Range Extent Comments
Astragalus arthuri occurs in the western United States in northeastern Oregon, southeastern Washington, and western Idaho (FNA 2023). Range extent was estimated using herbarium specimens, photo-based observations, and NatureServe Network occurrence data collected between 1994 and 2025 (RARECAT 2024, GBIF 2025, iNaturalist 2025, NatureServe 2025, SEINet 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 29 occurrences rangewide (RARECAT 2024, GBIF 2025, iNaturalist 2025, NatureServe 2025, SEINet 2025).
Threat Impact Comments
Astragalus arthuri is primarily threatened by livestock grazing and invasive plant species. While cattle do not appear to eat this plant, heavy grazing is associated with trampling and weed invasion (NatureServe 2025). Herbicide treatments of invasive species may impact populations of Astragalus arthuri.
Ecology & Habitat

Habitat

Astragalus arthurii grows in dry and stony meadows, on basaltic soils (Wildflowers.org 2020, FNA 2023).
Terrestrial Habitats
Grassland/herbaceous
Other Nations (1)
United StatesN3
ProvinceRankNative
IdahoS1Yes
OregonS3Yes
WashingtonS2Yes
Threat Assessments
ThreatScopeSeverityTiming
Unknown/undeterminedUnknownUnknownUnknown
2 - Agriculture & aquacultureLarge (31-70%)Slight or 1-10% pop. decline—
2.3 - Livestock farming & ranchingLarge (31-70%)Slight or 1-10% pop. decline—
8 - Invasive & other problematic species, genes & diseasesLarge (31-70%)Moderate or 11-30% pop. declineHigh (continuing)
8.1 - Invasive non-native/alien species/diseasesLarge (31-70%)Moderate or 11-30% pop. declineHigh (continuing)

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Plant Characteristics
DurationPERENNIAL
Economic Value (Genus)Yes
Roadless Areas (5)
Oregon (4)
AreaForestAcres
Imnaha FaceWallowa-Whitman National Forest29,575
Lord Flat Somers PointWallowa-Whitman National Forest67,738
Sheep DivideWallowa-Whitman National Forest16,201
Snake RiverWallowa-Whitman National Forest31,229
Washington (1)
AreaForestAcres
Asotin CreekUmatilla National Forest16,433
References (8)
  1. 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.
  2. Global Biodiversity Information Facility (GBIF). 2025. Global Biodiversity Information Facility (GBIF) data portal. Online. Available: https://www.gbif.org/ (accessed 2025).
  3. iNaturalist. 2025. Online. Available: https://www.inaturalist.org (accessed 2025).
  4. 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.
  5. NatureServe. 2025. NatureServe Network Biodiversity Location Data. NatureServe, Arlington, Virginia.
  6. NatureServe's Rapid Analysis of Rarity and Endangerment Conservation Assessment Tool (RARECAT). 2024. Version: 1.1.1 (released Oct 01, 2024).
  7. Southwest Environmental Information Network (SEINet). 2025. Collections Databases. Online. Available: https://swbiodiversity.org/seinet/collections/index.php (accessed 2025).
  8. Wildflower Center. 2020. Native Plant Database: <i>Astragalus arthurii</i>. Lady Bird Johnson Wildflower Center, University of Texas, Austin. Accessed: September 1, 2022. https://www.wildflower.org/plants/result.php?id_plant=ASAR8