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Home/Species/ Hamilton's Milkvetch

Astragalus hamiltonii

C.L. Porter

Hamilton's Milkvetch

G2Imperiled Found in 1 roadless area NatureServe Explorer →
G2ImperiledGlobal Rank
HighThreat Impact
Identity
Unique IDELEMENT_GLOBAL.2.152332
Element CodePDFAB0F3Y0
Record TypeSPECIES
ClassificationSpecies
Classification StatusStandard
Name CategoryVascular Plant
Endemicendemic to a single state or province
KingdomPlantae
PhylumAnthophyta
ClassDicotyledoneae
OrderFabales
FamilyFabaceae
GenusAstragalus
Synonyms
Astragalus lonchocarpus var. hamiltonii(C.L. Porter) Isely
Other Common Names
Hamilton's 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 Date2023-03-17
Change Date2023-03-17
Edition Date2023-03-17
Edition AuthorsRoth, E., rev. D. Stone (1997), rev. J. Handwerk (2006), rev. J. Handwerk (2011), rev. C. Nordman (2023).
Threat ImpactHigh
Range Extent250-1000 square km (about 100-400 square miles)
Number of Occurrences6 - 20
Rank Reasons
Hamilton's Milkvetch (Astragalus hamiltonii) occurs in the western United States, it is endemic to northeastern Utah, concentrated in the central Uinta Basin. Threats include spring and summer livestock grazing, recreational off road vehicle activities, nonnative invasive plant species such as cheatgrass (Bromus tectorum), oil and gas exploration and development, and potential future tar sands extraction. Hamilton's Milkvetch is less exposed to these threats due to its habitat being on less accessible slopes. The total population size has not been documented, but was estimated in 1995 to be 10,000-15,000 individuals, and in 2010 to be greater than 5,800 individuals.
Range Extent Comments
Hamilton's Milkvetch (Astragalus hamiltonii) occurs in the western United States, it is endemic to northeastern Utah, the central Uinta Basin (west of Vernal in Uintah County), with some locations in the eastern Uinta Basin near the Green River, in Uintah County. The range extent is estimated to be 957 square kilometers (NatureServe 2023, SEINet 2023, USFWS 2011, Utah Natural Heritage Program 2021, Welsh et al. 2015). It has been erroneously reported from the Coyote Basin and Deadman's Bench areas (further south) near Bonanza in eastern Uintah County, and from Moffat and Rio Blanco counties, northwestern Colorado. These reports are based on misidentified specimens of A. lonchocarpus (a common, widespread, and variable species). It has also been erroneously reported from Duchesne County, Utah, based on a mislabeled specimen (Stone/UTHP 1997). Records from near the Green River in Daggett County, Utah need further verification.
Occurrences Comments
There are about 17 element occurrences in Utah, based on 2 kilometer separation distances (NatureServe 2023, Utah Natural Heritage Program 2021). It has been suggested that the known occurrences may be linked by contiguous habitat, and may be one large population or metapopulation (USFWS 2011).
Threat Impact Comments
There are several threats to Hamiliton's Milkvetch, these include spring and summer livestock grazing, recreational off road vehicle activities, nonnative invasive plant species such as cheatgrass (Bromus tectorum), oil and gas exploration and development, and potential future tar sands extraction (Alexander 2016, USFWS 2011). Hamiliton's Milkvetch is less exposed to these threats due to its habitat being on slopes, rather than on more accessible flat areas. None of these threats, individually are considered high impact (USFWS 2011). Off road vehicle use is a major threat at some of the sites (Heil and Melton 1995).
Ecology & Habitat

Diagnostic Characteristics

"The broad leaflets of Astragalus hamiltonii and tendency to coarse pods and rather compact racemes at anthesis set this distinctive plant apart (from A. lonchocarpus). The calyx is often brown and the petals yellow when dry, forming a distinctive contrast seldom evident in A. lonchocarpus" (Welsh et al. 2015).

Habitat

Hamilton's Milkvetch (Astragalus hamiltonii) occurs primarily in the Uinta Basin on reddish, erosive sandy clay loam soils on semi-barren, benches and rapidly eroding slopes of the Duchesne River Formation, and Wasatch Formation, and less commonly Mowry Shale, Dakota, and other formations, in warm desert scrub communities, sometimes with scattered juniper and pinyon, and along old road cuts and road beds at 1500-1940 meters (4920 to 6365 feet) elevation (Barneby 1989, Heil and Melton 1995, USFWS 2011, Welsh et al. 2015).

Reproduction

Hamilton's Milkvetch (Astragalus hamiltonii) is assumed to reproduce mainly by outcrossing, that is, cross-fertilization (Heil and Melton 1995).
Terrestrial Habitats
Shrubland/chaparralSavannaDesert
Other Nations (1)
United StatesN2
ProvinceRankNative
UtahS2Yes
Threat Assessments
ThreatScopeSeverityTiming
1 - Residential & commercial developmentRestricted (11-30%)Slight or 1-10% pop. declineHigh (continuing)
2 - Agriculture & aquacultureLarge (31-70%)Moderate or 11-30% pop. declineHigh (continuing)
2.3 - Livestock farming & ranchingLarge (31-70%)Moderate or 11-30% pop. declineHigh (continuing)
3 - Energy production & miningSmall (1-10%)Negligible or <1% pop. declineHigh (continuing)
3.1 - Oil & gas drillingSmall (1-10%)Negligible or <1% pop. declineHigh (continuing)
6 - Human intrusions & disturbanceSmall (1-10%)Moderate or 11-30% pop. declineHigh (continuing)
6.1 - Recreational activitiesSmall (1-10%)Moderate or 11-30% pop. declineHigh (continuing)
8 - Invasive & other problematic species, genes & diseasesLarge (31-70%)Slight or 1-10% pop. declineHigh (continuing)
8.1 - Invasive non-native/alien species/diseasesLarge (31-70%)Slight or 1-10% pop. declineHigh (continuing)
11 - Climate change & severe weatherPervasive (71-100%)Moderate - slightHigh (continuing)

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Plant Characteristics
DurationPERENNIAL
Economic Value (Genus)Yes
Roadless Areas (1)
Utah (1)
AreaForestAcres
0419020Ashley National Forest355,684
References (14)
  1. Albee, B.J., L.M. Shultz, and S. Goodrich. 1988. Atlas of the vascular plants of Utah. Utah Museum Natural History Occasional Publication 7, Salt Lake City, Utah. 670 pp.
  2. Alexander, J. 2016. The Utah Native Plant Society Rare Plant List: Version 2. Calochortiana. 3: 1-248.
  3. Barneby, R.C. 1989. Fabales. In A. Cronquist, A.H. Holmgren, N.H. Holmgren, J.L. Reveal, and P.K. Holmgren (eds.). Intermountain flora: Vascular plants of the Intermountain West, U.S.A. Vol. 3, Part B. New York Botanical Garden, Bronx. 279 pp.
  4. Colorado Natural Heritage Program. 2005. The Second Annual Colorado Rare Plant Symposium: G1 Plants of Colorado. Symposium Minutes. Available on-line http://www.cnhp.colostate.edu/teams/botany.asp#symposia.
  5. Colorado Natural Heritage Program. 2006. Biological Conservation Datasystem. Colorado State University, Ft. Collins, CO.
  6. Heil, K.D., and B. Melton. 1995. Status report for Astragalus hamiltonii C.L. Porter. Prepared for the Bureau of Land Management, Vernal District Office, Vernal, Utah. 20 pp. + appendices.
  7. Jennings, W. 1994. Personal communication with CNHP staff.
  8. 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.
  9. NatureServe. 2023. NatureServe Network Biodiversity Location Data. NatureServe, Arlington, Virginia.
  10. Southwest Environmental Information Network (SEINet). 2023. Collections Databases. Online. Available: https://swbiodiversity.org/seinet/collections/index.php (accessed 2023).
  11. U.S. Fish and Wildlife Service (USFWS). 2011. 12-Month Finding on a Petition To List Astragalus hamiltonii, Penstemon flowersii, Eriogonum soredium, Lepidium ostleri, and Trifolium friscanum as Endangered or Threatened. Federal Register 76(36):10166-10203.
  12. Utah Natural Heritage Program. 2006. Biological Conservation Datasystem. Salt Lake City, UT
  13. Utah Natural Heritage Program. 2021. Utah Rare Plant Database (accessed 2021).
  14. Welsh, S.L., N.D. Atwood, S. Goodrich, and L.C. Higgins. (Eds). 2015. A Utah flora, fifth edition, revised 2015. Monte L. Bean Life Science Museum, Provo, Utah. 987 pp.