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Home/Species/ Lost River Milkvetch

Astragalus amnis-amissi

Barneby ex C.L. Hitchc.

Lost River Milkvetch

G3Vulnerable Found in 1 roadless area NatureServe Explorer →
G3VulnerableGlobal Rank
LowThreat Impact
Identity
Unique IDELEMENT_GLOBAL.2.131354
Element CodePDFAB0F0J0
Record TypeSPECIES
ClassificationSpecies
Classification StatusStandard
Name CategoryVascular Plant
Endemicendemic to a single state or province
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 Date2025-01-28
Change Date2025-01-28
Edition Date2025-01-28
Edition AuthorsMancuso, M./Gries, D. (1999), rev. Johnson, J. (2025)
Threat ImpactLow
Range Extent250-1000 square km (about 100-400 square miles)
Number of Occurrences6 - 20
Rank Reasons
Astragalus amnis-amissi is a perennial herb that is endemic to east-central Idaho. It was known only from the type locality in Pass Creek Gorge until the late 1970's, when additional populations were discovered. It is presently known from 3 occurrences with an additional 10 historical occurrences. The milkvetch occurs in Custer and Butte counties on land managed by the Forest Service and the Bureau of Land Management. The only known immediate threat to this habitat is invasion by Bromus tectorum and Euphorbia esula.
Range Extent Comments
Astragalus amnis-amissi is endemic to east-central Idaho, known from Custer and Butte Counties, mostly in the southern Lemhi, Lost River, and Pioneer ranges (Steele et. al. 1981, Daines 2023, NatureServe 2024). Range extent was estimated to be 575 sq km using herbarium specimens, photo-based observation, and NatureServe Network occurrence data collected between 1993 and 2024, and estimated at 1,000 sq km when historical collections are included (GBIF 2024, NatureServe 2024, SEINet 2024, iNaturalist 2024, Daines 2023).
Occurrences Comments
Based on herbarium records, photo-based observation, and NatureServe Network occurrence data documented between 1993 and 2024, and anecdotal evidence, there are 7 occurrences rangewide (GBIF 2024, NatureServe 2024, SEINet 2024, iNaturalist 2024, Daines 2023). An additional 6 occurrences are historical, but without surveys, the persistence of plants at them is unknown (NatureServe 2024). One historical occurrence was searched in 2020 and no plants were found (Daines 2023).
Threat Impact Comments
The canyons and cliffs where this species grows are largely inaccessible to motorized recreation and livestock. Some occurrences are threatened by nearby invasive plant occurrences. Evidence of recreational rock climbing has been seen at some occurrences (Daines 2023).
Ecology & Habitat

Diagnostic Characteristics

The Lost River milkvetch is closely related to the Challis milkvetch (Astragalus amblytropis), but the essentially simple stems arising from a superficial root-crown and caudex, the slightly larger flowers, and especially the smaller, semibilocular, relatively few-ovulate pod provide significant differences (Barneby 1964).

Habitat

Astragalus amnis-amissi grows in ledges and crevices in near-vertical limestone rock and in stable talus at bases of cliffs in Douglas-fir, Rocky Mountain maple, or mountain mahogany woodlands (Steele et. al. 1981).
Terrestrial Habitats
Woodland - HardwoodWoodland - ConiferWoodland - MixedCliff
Other Nations (1)
United StatesN3
ProvinceRankNative
IdahoS3Yes
Threat Assessments
ThreatScopeSeverityTiming
6 - Human intrusions & disturbanceRestricted (11-30%)Moderate or 11-30% pop. declineHigh (continuing)
6.1 - Recreational activitiesRestricted (11-30%)Moderate or 11-30% pop. declineHigh (continuing)
8 - Invasive & other problematic species, genes & diseasesRestricted (11-30%)Moderate or 11-30% pop. declineHigh (continuing)
8.1 - Invasive non-native/alien species/diseasesRestricted (11-30%)Moderate or 11-30% pop. declineHigh (continuing)
8.1.2 - Named speciesRestricted (11-30%)Moderate or 11-30% pop. declineHigh (continuing)

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Plant Characteristics
DurationPERENNIAL
Economic Value (Genus)Yes
Roadless Areas (1)
Idaho (1)
AreaForestAcres
Borah PeakSalmon-Challis National Forest130,463
References (10)
  1. Barneby, R.C. 1964. Atlas of North American Astragalus. 2 Vols. New York Botanical Garden, Bronx, New York. 1188 pp.
  2. Daines, M. Distribution of Astragalus amnis-amissi (Fabaceae), a plant endemic to east-central Idaho. Western North American Naturalist 83(1), pp. 146–151.
  3. Henderson, D.M., S. Brunsfeld, and P. Brunsfeld. 1981. Noteworthy collections. Madrono 28(2):86-90.
  4. iNaturalist. 2024. Online. Available: https://www.inaturalist.org (accessed 2024).
  5. 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.
  6. Mancuso, Michael. Botanist, Idaho Conservation Data Center, Boise, Idaho. Personal communication.
  7. NatureServe. 2024. NatureServe Network Biodiversity Location Data. NatureServe, Arlington, Virginia.
  8. Southwest Environmental Information Network (SEINet). 2024. Collections Databases. Online. Available: https://swbiodiversity.org/seinet/collections/index.php (accessed 2024).
  9. Steele, B., F. Johnson, and S. Brunsfeld, eds. 1981. Vascular plant species of concern in Idaho. Forest, Wildlife and Range Experiment Station, Moscow, ID. 161 pp.
  10. U.S. Forest Service, Intermountain Region (USFS). 1990. Idaho and Wyoming endangered and sensitive plant field guide. U.S. Forest Service, Intermountain Region, Ogden, UT. 192 pp.