Astragalus molybdenus
Author: Barneby

Leadville milkvetch

Fabaceae (Pea Family)

Close up of Astragalus molybdenus by Bernadette Kuhn.
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Ranks and Status

Global rank: G3
State rank: S2
Federal protection status: None
State protection status: None

[+] Description and Phenology

Astragalus molybdenus by Janet Wingate.
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General description: Astragalus molybdenus is a perennial herb. It is a low-growing, loosely tufted, rhizomatous plant (Ladyman 2003). It is typically 2.5 to 7.6 cm (1 to 3 inches) tall. Leaves are pinnately compound with 9 to 25 (usually 13-19) silvery-gray, oval-oblong leaflets (Ladyman 2003, Ray 2001). Flowers are pale purplish or pinkish, and may have whitish stripes (Ladyman 2003, Ray 2001). There are conspicuous black hairs on the calyx tube. Plants have one or two clusters of two or three flowers each (Ray 2001). The legumes are 7 to 10 mm (0.25 to 0.4 inch) long, and are slightly in-curved (Ladyman 2003).

Look Alikes: Astragalus robbinsii and A. aboriginum var. glabriusculus are larger plants with stipitate pods (Spackman et al. 1997, Ladyman 2003, NatureServe 2011). Astragalus alpinus had bluer flowers, and reflexed stipitate pods (Ladyman 2003). Oxytropis deflexa has spreading or reflexed hairs on the stem (Ladyman 2003).

Phenology: In Colorado, flowering of Astragalus molybdenus may begin in late June and continue through early August. Fruits are maturing through August and September (Ray 2001, Ladyman 2003).

[+] Herbarium Photos

Images of Astragalus molybdenus housed at the Colorado State University Herbarium.

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[+] Habitat

Habitat of Astragalus molybdenus by Bernadette Kuhn.
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Astragalus molybdenus is one of a few alpine Astragalus species (Ladyman 2003). In Colorado, populations are found on sparsely vegetated, rocky slopes, and on turf-covered hillsides (Spackman, et al. 1997, Ladyman 2003). They occur on all aspects, with fewest facing northeast (Ladyman 2003). It is found on slopes of up to 70 percent, although most are less than 35 percent (Ladyman 2003). Populations are found on limestone or in calcareous soils (Spackman, et al., 1997, Ray 2001, Ladyman 2003). Stable habitats are preferred. Species associated with Astragalus molybdenus include Achillea millefolium, Zigadenus elegans, Astragalus alpinus, Besseya alpina, Carex rupestris, Claytonia megarhiza, Erigeron ursinus, Geum rossii, Silene acaulis, Smelowskia calycina, and Trisetum spicatum (Ray 2001, Ladyman 2003).

Elevation Range: 9,409 - 14,137 feet (2,868 - 4,309 meters)

[+] Distribution

Distribution of Astragalus molybenus in Colorado according to mapped land ownership/management boundaries (CNHP 2017, COMaP).
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Distribution of Astragalus molybenus in Colorado.
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Colorado endemic: No
Global range: Astragalus molybdenus in the broad sense occurs in Montana, Wyoming, and Colorado (USDA NRCS 2017). According to Lavin and Marriott (1997): A. molybdenus in the strict sense is endemic to a relatively small region in central Colorado in Gunnison, Park, Pitkin, and Summit Counties; A. shultziorum (included in A. molybdenus here) is endemic to Wyoming, from the Salt River and Wyoming Ranges in Lincoln County, the Gros Ventre Mountains in Sublette County, and the Teton Range in Teton County; and A. lackschewitzii (included in A. molybdenus here) is endemic to the Rocky Mountain front range in west-central Montana, Teton County.
State range: In Colorado, this species has been found in Chaffee, Gunnison, Hinsdale, Lake, Park, Pitkin, and Summit counties. Weber and Wittmann (2012) report that this species is also found in Wyoming, and in Colorado is known from the Mosquito, Elk, and Saguache mountain ranges. One report from Hinsdale County is in the San Juan Mountains.

[+] Threats and Management Issues

Mining activity is noted on four occurrences. Roads are reported as disturbances at three sites. Colorado climate scenarios for 2050 suggest temperature will increase by 3-7 F and precipitation may decrease or increase. The impact to any given rare plant habitat is likely to vary. Long-term monitoring that includes weather and soil moisture data is critical to understanding climate impacts.

[+] References

    • Ackerfield, J. 2015. Flora of Colorado. Brit Press, Botanical Research Institute of Texas, Fort Worth, TX. 818 pp.
    • Barneby, R. C. 1964. Atlas of North American Astragalus. Memoirs of New York Botanical Garden, vol. 13. New York Botanical Garden, Bronx, NY.
    • Colorado Natural Heritage Program and the Geospatial Centroid. 2017. The Colorado Ownership and Protection Map (COMaP). Colorado State University, Ft. Collins, CO.
    • Harrington, H. D. 1954. Manual of the Plants of Colorado. Sage Books, Denver, CO. 666 pp.
    • 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.
    • Lavin, M. and H. Marriott. 1997. Astragalus molybdenus s.l. (Leguminosae): Higher taxonomic relationships and identity of constituent species. Systematic Botany 22(2):199-217.
    • Lavin, M., S. Mathews, C. Hughes, H. Marriott and S. Shelly. 1990. Intraspecific chloroplast DNA diversity is high in some wild species of Leguminosae. Amer. J. Bot. 77 (supplement):144 (abstract).
    • Ryke, N., D. Winters, L. McMartin and S. Vest. 1994. Threatened, Endangered and Sensitive Species of the Pike and San Isabel National Forests and Comanche and Cimarron National Grasslands. May 25, 1994.
    • Schassberger, L. A. and J. S. Shelly. 1990. Status review and taxonomic studies of Astragalus molybdenus, Lewis and Clark National Forest. Unpublished report. Montana Natural Heritage Program, Helena, MT. 45 pp.
    • Shelly, J. S. 1989. Field surveys in Teton County, 7-10, 21-23, and 28-30 August (ASTRAGALUS LACKSCHEWITZII).
    • 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.
    • USDA, Natural Resources Conservation Service, PLANTS Database [USDA PLANTS]. Accessed 2017.
    • Weber, W. A. and R. C. Wittmann. 2012. Colorado Flora, Eastern Slope, A Field Guide to the Vascular Plants, Fourth Edition. Boulder, Colorado. 555 pp.
    • Weber, W. A. and R. C. Wittmann. 2012. Colorado Flora, Western Slope, A Field Guide to the Vascular Plants, Fourth Edition. Boulder, Colorado. 532 pp.

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