Astragalus anisus
Author: M.E. Jones


Gunnison milkvetch


Fabaceae (Pea Family)

Close up of Astragalus anisus in flower by Lori Brummer
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Close up of Astragalus anisus by Lori Brummer
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Close up of Astragalus anisus pods by Barry Johnston
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Ranks and Status

Global rank: G2G3
State rank: S2S3
Federal protection status: BLM Sensitive
State protection status: None

[+] Description and Phenology

Astragalus anisus by Gemma Delfinado
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Astragalus anisus by M.E. Jones
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General description: Astragalus anisus is a short, tufted perennial with basal leaves that arise from a very short stem above a woody taproot. The caudex, or stem base, often shows the thatched remains of old leaves. The leaves are pinnately compound, up to 7 cm long, with 11 to 15 leaflets. The entire plant appears silvery-gray due to the presence of numerous hairs of a characteristic dolabriform (ax or pick-shaped) shape. Flowers are borne on short racemes and are typically pink-purple in color. The pods (fruits) are short (1.3 to 1.8 cm in length) and almost round, though somewhat compressed from front to back, and of a fleshy texture with flat-lying hairs. Fruits are originally green in color, becoming brown with maturity. Each fruit contains 28 to 40 ovules. Seeds are smooth, black, and small (2.0 to 2.4 mm in length). The fruit is bilocular (has two chambers), often appears red or orange when inflated, and splits into two sections when dry (Decker and Anderson 2004).

Look Alikes: Astragalus anisus could be confused with A. missouriensis which also grows in the Gunnison Basin, but has a mottled pod. The two species can only be distinguished by their fruit.

Phenology: Flowers May-June (Spackman et al. 1997, Ackerfield 2012).

[+] Habitat

Habitat of Astragalus anisus by Bernadette Kuhn
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Found within Sagebrush Shrubland (dominated by Artemisia tridentata ssp. tridentata, Artemisia tridentata ssp. vaseyana, Artemisia tridentata ssp. wyomingensis, or Artemisia cana) and Sagebrush Shrub Steppe (dominated by Artemisia nova or Artemisia arbuscula) ecological system types; primarily within the Dry Sagebrush Shrubland type. Usually found in fairly open sites where sagebrush shrubs do not form a closed canopy, but sometimes shelters under low sagebrush plants. Sites are characterized by the absence of trees, moderate shrub cover, moderate understory cover, and extensive bare ground. Found on flats on the floor of the Gunnison Basin and on hillsides. Usually on sandy clay to gravelly soils overlying granitic bedrock; parent materials include rhyolite, tuff, gneiss, and schist. Slopes range 0 - 34% (average 17.3%) and aspects are usually west-facing. Other associated species include Phlox hoodii, Bouteloua gracilis, Poa fendleriana, and Stipa pinetorum.  (Decker and Anderson 2004).

Elevation Range: 7,523 - 9,741 feet (2,293 - 2,969 meters)

[+] Distribution

Distribution of Astragalus anisus in Colorado.
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Colorado endemic: Yes
Global range: The species entire global range is contained within the upper Gunnison Basin, in Gunnison and Saguache counties, Colorado. Estimated range is 1,962 square kilometers (757 square miles), calculated in GIS in 2008 by the Colorado Natural Heritage Program by drawing a minimum convex polygon around the known occurrences.

[+] Threats and Management Issues

Summary results of an analysis of the status of Astragalus anisus based on several ranking factors. This species was concluded to be “effectively conserved”. From Rondeau et al. 2011.
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The greatest threat to this species and its conservation is lack of awareness that it exists and it's narrow-endemic status. However, to increase awareness and protection Best Management Practices have been developed (Panjabi and Smith 2014).  Another primary threat at this time is considered to be road building (Decker and Anderson 2004, Rondeau et al. 2011). Other threats are from off-road vehicle use, non-motorized recreation, non-native species invasion, grazing, residential development, fire suppression, resource extraction, and global climate change. Climate change has shifted the blooming time for this species to more than a month earlier than it bloomed in the 1800s (Munson and Sher 2015).   A lack of systematic tracking of population trends and conditions and a lack of knowledge about the species' basic life cycle also contribute to the possibility that one or more of these factors will threaten its long-term persistence (Decker and Anderson 2004).

[+] References

    • Ackerfield, J. 2012. The Flora of Colorado. Colorado State University Herbarium. 433 pp.
    • Barneby, R. C. 1964. Atlas of North American Astragalus. Memoirs of New York Botanical Garden, vol. 13. New York Botanical Garden, Bronx, NY.
    • Barneby, R.C. 1964. Atlas of North American Astragalus. 2 Vols. New York Botanical Garden, Bronx, New York. 1188 pp.
    • Decker, K. and D.G. Anderson. 2004. Astragalus anisus M.E. Jones (Gunnison milkvetch): a technical conservation assessment. USDA Forest Service, Rocky Mountain Region. Online. Available: http://www.fs.fed.us/r2/projects/scp/assessments/astragalusanisus.pdf (Accessed 2006).
    • Isely, D. 1998. Native and naturalized Leguminosae (Fabaceae) of the United States (exclusive of Alaska and Hawaii). Monte L. Bean Life Science Museum, Brigham Young University; MLBM Press, Provo, Utah. 1007 pp.
    • Jones, M.E. 1923. Revision of North-American Species of Astragalus. Salt Lake City, UT.
    • 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.
    • Munson, S. M. and A. A. Sher. 2015. Long-term shifts in the phenology of rare and endemic Rocky Mountain plants. American Journal of Botany 102: 1268-1276.
    • Neely, B., R. Rondeau, J. Sanderson, C. Pague, B. Kuhn, J. Siemers, L. Grunau, J. Robertson, P. McCarthy, J. Barsugli, T. Schulz, and C. Knapp. Editors. Gunnison Basin: Vulnerability Assessment for the Gunnison Climate Working Group by The Nature Conservancy, Colorado Natural Heritage Program, Western Water Assessment, University of Colorado, Boulder, and University of Alaska, Fairbanks. Project of the Southwest Climate Change Initiative.
    • Neely, B., S. Panjabi, E. Lane, P. Lewis, C. Dawson, A. Kratz, B. Kurzel, T. Hogan, J. Handwerk, S. Krishnan, J. Neale, and N. Ripley. 2009. Colorado Rare Plant Conservation Strategy, Developed by the Colorado Rare Plant conservation Initiative. The Nature Conservancy, Boulder, Colorado, 117 pp.
    • Panjabi, S.S. and G. Smith, 2014. Recommended best management practices for Gunnison milkvetch (Astragalus anisus): practices developed to reduce the impacts of road maintenance activities to plants of concern. Colorado Natural Heritage Program, Colorado State University, Fort Collins, Colorado. Accessed online on: Dec 7, 2015 at https://www.codot.gov/programs/environmental/wildlife/guidelines/rare-plant-bmps/astragalus-anisus
    • Rondeau, R., K. Decker, J. Handwerk, J. Siemers, L. Grunau, and C. Pague. 2011. The state of Colorado's biodiversity 2011. Prepared for The Nature Conservancy. Colorado Natural Heritage Program, Colorado State University, Fort Collins, Colorado.
    • Rondeau, R., K. Decker, J. Handwerk, J. Siemers, L. Grunau, and C. Pague. 2011. The state of Colorado's biodiversity 2011. Prepared for The Nature Conservancy. Colorado Natural Heritage Program, Colorado State University, Fort Collins, Colorado.
    • Rydberg, P.A. 1906. Flora of Colorado. Agricultural Experiment Station of the Colorado Agricultural College, Fort Collins.
    • Spackman, S., B. Jennings, J. Coles, C. Dawson, M. Minton, A. Kratz, and C. Spurrier. (Web authors: Johnson, C.S. and M. Barry). 1999. Colorado rare plant field guide. Prepared for Bureau of Land Management, U.S. Forest Service and U.S. Fish and Wildlife Service by Colorado Natural Heritage Program. Online. Available: http://www.cnhp.colostate.edu/rareplants/cover.html (Accessed 2006)
    • Spackman, S., B. Jennings, J. Coles, C. Dawson, M. Minton, A. Kratz, and C. Spurrier. 1997. Colorado rare plant field guide. Prepared for Bureau of Land Management, U.S. Forest Service and U.S. Fish and Wildlife Service by Colorado Natural Heritage Program.
    • The Colorado Native Plant Society. 1997. Rare Plants of Colorado, second edition. Falcon Press Publishing Co.,Inc. Helena, Montana. 105pp.
    • USDA, NRCS. 2013. The PLANTS Database. National Plant Data Team, Greensboro, NC 27401-4901 USA.
    • Wasson, A. 1998. Astragalus anisus in the Gunnison Basin: A Demographic Study.
    • Wasson, A. 1998. Astragalus anisus in the Gunnison Basin: A Demographic Study.
    • Welsh, S.L. 2007. North American Species of Astragalus Linnaeus (Leguminosae) A Taxonomic Revision. Brigham Young University, Provo, Utah. 932 pp.

Last Updated

2013-08-23