Home/Species/ Precocious Milkvetch

Astragalus proimanthus

Barneby

Precocious Milkvetch

G2Imperiled Found in 1 roadless area NatureServe Explorer →

G2ImperiledGlobal Rank

High - mediumThreat Impact

Identity

Unique IDELEMENT_GLOBAL.2.143090

Element CodePDFAB0F730

Record TypeSPECIES

ClassificationSpecies

Classification StatusStandard

Name CategoryVascular Plant

Endemicendemic to a single state or province

KingdomPlantae

PhylumAnthophyta

ClassDicotyledoneae

OrderFabales

FamilyFabaceae

GenusAstragalus

Synonyms

Orophaca proimantha(Barneby) Isely

Other Common Names

precocious 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.

Taxonomic Comments

Thought to be a distinct species. Very close morphologically to A. hyalinus, but blooms earlier and does not overlap in range. Material of A. proimanthus collected in 1989 for cDNA studies to be done in 1990 (MtSU).

Conservation Status

Rank Method Rank calculation - Biotics v2

Review Date2024-06-14

Change Date2024-06-14

Edition Date2024-06-14

Edition AuthorsMARRIOTT, H. (rev. W. Fertig/K. Maybury 6/96), rev. Soteropoulos (2024)

Threat ImpactHigh - medium

Range Extent<100 square km (less than about 40 square miles)

Number of Occurrences1 - 5

Rank Reasons

Astragalus proimanthus is a perennial forb in cushion plant or bunchgrass communities on sparsely vegetated rims and bluffs endemic to the Henry's Fork River in the southern Green River Basin in southwestern Sweetwater County, Wyoming in the western United States. Population size is estimated to be over 10,000 individuals in fewer than five occurrences. All known occurrences are located on lands managed by the Bureau of Land Management, though the multiple use management area presents several threats from mineral development, grazing, and recreation. Trend data are difficult to estimate due to differences in survey methodology. Short-term trends between the 1980s and a 1999 survey could be as great as a 47.5% decline, though recent communication suggests relatively stable trends. Monitoring of populations should be conducted to improve our understanding of reproduction, plant abundance, threats, and trends, as well as continuing conservation measures to protect the species.

Range Extent Comments

Astragalus proimanthus is a narrow endemic restricted to the bluffs of the Henry's Fork River and vicinity of McKinnon in the southern Green River Basin in southwestern Sweetwater County, Wyoming in the western United States (Fertig and Welp 2001, FNA 2023). The entire global distribution of the species is limited to 76 sq. km. (Fertig and Welp 2001, Jouseau 2016).

Occurrences Comments

This species is known from four occurrences, three of which could be considered a population complex (Heidel, pers. comm., 2024).

Threat Impact Comments

This species is threatened by the multiple use management area present through most of its range, with an emphasis on mineral development, grazing, and recreation (Fertig and Welp 2001). Threats include road construction, off-road vehicle recreation, oil and gas development, disturbance associated with a garbage dump, and habitat modifications stemming from range improvement projects (Fertig and Welp 2001, Jouseau 2016). Direct threats from grazing are probably less significant compared to secondary impacts, including trampling, trailing, soil compaction, erosion, and the spread of noxious weeds (Fertig and Welp 2001). In wet conditions during 2015, a landslide was presumably caused by horses, though the habitat may be prone to natural slumping during prolonged rainy periods (Jouseau 2016).

Ecology & Habitat

Habitat

"Astragalus proimanthus occurs primarily on sparsely vegetated rims and gullied upper slopes of benches, bluffs, and mesa-like ridges at elevations of 6400-7200 feet (1950-2195 m). Populations are typically found in cushion plant/bunchgrass communities dominated by Phlox hoodii, Haplopappus nuttallii, Cryptantha sericea, and Elymus spicatus in openings within Artemisia tridentata or Juniperus osteosperma grasslands. Occasionally, colonies may also occur on open toe slopes of ridges within a matrix of Artemisia nova, Sarcobatus vermiculatus, Juniperus osteosperma, and Grayia spinosa. Vegetation cover is typically less than 5-10%. Soils are whitish, fine-textured, dry, shallow, calcareous shale clays covered with a dense layer of coarse cobbles, whitish shaley flakes, and dark volcanic rock" (Fertig and Welp 2001).

Terrestrial Habitats

Grassland/herbaceousBare rock/talus/scree

Other Nations (1)

United StatesN2

Province	Rank	Native
Wyoming	S2	Yes

Threat Assessments

Threat	Scope	Severity	Timing
2 - Agriculture & aquaculture	Large (31-70%)	Moderate - slight	High (continuing)
2.3 - Livestock farming & ranching	Large (31-70%)	Moderate - slight	High (continuing)
3 - Energy production & mining	Large (31-70%)	Moderate - slight	Moderate - low
3.1 - Oil & gas drilling	Large (31-70%)	Moderate - slight	Moderate - low
4 - Transportation & service corridors	Unknown	Unknown	Insignificant/negligible or past
4.1 - Roads & railroads	Unknown	Unknown	Insignificant/negligible or past
6 - Human intrusions & disturbance	Large (31-70%)	Moderate - slight	High (continuing)
6.1 - Recreational activities	Large (31-70%)	Moderate - slight	High (continuing)
9 - Pollution	Small (1-10%)	Serious - moderate	High (continuing)
9.4 - Garbage & solid waste	Small (1-10%)	Serious - moderate	High (continuing)

Plant Characteristics

DurationPERENNIAL

Economic Value (Genus)Yes

Roadless Areas (1)

Utah (1)

Area	Forest	Acres
0419020	Ashley National Forest	355,684

References (10)

Barneby, R.C. 1964. Atlas of North American Astragalus. 2 Vols. New York Botanical Garden, Bronx, New York. 1188 pp.
Clark, T. W., and R. D. Dorn (eds.). 1981. Rare and endangered vascular plants and vertebrates of Wyoming. Tim W. Clark and Robert D. Dorn, Jackson, WY. 66 pp.
Fertig, W. and L. Welp. 2001. Status of precocious milkvetch (Astragalus proimanthus) in southwest Wyoming. Unpublished report prepared for the Bureau of Land Management Wyoming State Office by the Wyoming Natural Diversity Database, Laramie, WY.
Fertig, W., C. Refsdal, and J. Whipple. 1994. Wyoming rare plant field guide. Wyoming Rare Plant Technical Committee, Cheyenne. No pagination.
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.
Heidel, Bonnie. Personal communication. Lead Botanist, University of Wyoming, Wyoming Natural Diversity Database, Laramie, WY.
Jouseau, M.R.G. 2016. Survey for precocious milkvetch (Astragalus proimanthus Barneby) in southwestern Wyoming. Unpublished report prepared for Bureau of Land Management – Rock Springs Field Office and State Office and Wyoming Natural Diversity Database, Laramie, WY.
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.
Marriott, H.J. 1989e. Inventory and monitoring of Astragalus proimanthus (precocious milkvetch). Unpublished report prepared for the Bureau of Land Management, Rock Springs District. 17 pp + appendices.
Roberts, M.L. 1977. Systematics of the Orophaca Astragali M.S. thesis. Univ. of Wyoming, Laramie, WY. 101pp.

Astragalus proimanthus

Habitat

—