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Astragalus michauxii (Kuntze) F.J. Herm.
Sandhill Milkvetch
Federal Protection: No US federal protection
State Protection: Threatened
Global Rank: G3
State Rank: S2
Element Locations Tracked in Biotics: Yes
SWAP 2015 Species of Greatest Conservation Need (SGCN): Yes
SWAP 2025 Species of Greatest Conservation Need (SGCN): Yes
2025 SGCN Priority Tier: High Conservation Concern
Element Occurrences (EOs) in Georgia: 29
Habitat Summary for element in Georgia: Longleaf pine-wiregrass savannas; turkey oak scrub
Perennial herb with erect stems 1 - 3.3 feet (30 - 100 cm) tall. Leaves are up to 6 inches (15 cm) long, alternate, with 21 - 31 oval or oblong leaflets, each 0.24 - 1 inch (6 - 25 mm) long, thick or leathery, sometimes thinly hairy; leaflets may be both opposite and alternate. Flower clusters arise in the angles between the stem and the upper 2 - 6 leaves, with 10 - 40 flowers per cluster. Flowers are 0.5 - 0.7 inch (1.2 - 1.8 cm) long, pale pink or purple, typical of pea flowers with an erect banner petal and 2 wing petals enclosing the keel petal. Fruit is a smooth, leathery, upcurved pod, about 1 inch (2 - 3 cm) long and 0.2 inch (4 - 6 mm) wide.
Hairy Milk-vetch (Astragalus villosus) is a sprawling, mat-forming plant with densely hairy stems and yellowish flowers.
Goat’s-rue (Tephrosia virginiana) holds its flower cluster at the top of the main stem, and the flowers are bicolored, pink and cream.
Canada Milk-vetch (Astragalus canadensis) occurs along one roadside in Dade County, in northwest Georgia, over limestone bedrock. It is an erect plant with creamy-yellow flowers; its pods are about 0.5 inch (1 - 1.5 cm) long, and are upcurved, with a rough, leathery surface.
Longleaf Pine-Wiregrass sandhills, pine woodlands, and turkey oak-rosemary scrub.
Sandhill Milk-vetch is a perennial herb that reproduces sexually by seed; it does not spread vegetatively. Flowers of other species of milk-vetch are pollinated by bumble bees, solitary bees, and flies; it is likely that these insects also pollinate Sandhill Milk-vetch. Seeds of Sandhill Milk-vetch have tough outer and inner coats that slow down or prevent germination unless the seed coats are broken by scarification of some sort, such as passage through an animal's gut.
Fire has long been a factor in shaping Astragalus michauxii habitat. However, recent research indicates that too frequent fire has a negative impact on survival, flowering, and fruit production by this species. The researchers recommend a fire return interval no sooner than every 3 years. Fire is still recommended to reduce litter accumulation and encroachment by woody species in sandhills, both of which would have a negative effect on this species.
Many members of the genus Astragalus produce toxins and are known as "locoweeds" for their effect on cattle. Sandhill Milk-vetch produces miserotoxin, which may produce severe respiratory distress, weakness, coma, and death in cattle that eat it.
Surveys are best conducted during flowering (May–June) and fruiting (June–October).
Georgia, Florida, Alabama, South Carolina, and North Carolina.
Fire suppression in sandhills, pine straw raking, conversion of sandhill habitat to pine plantations and developments.
| Threat 1 | Threat 2 | Threat 3 | |
|---|---|---|---|
| General Threat | Invasive & other problematic species, genes & diseases | Energy production & mining | Invasive & other problematic species, genes & diseases |
| Specific Threat | None | None | None |
Astragalus michauxii is ranked S2 by the Georgia Department of Natural Resources, indicating that it is imperiled in the state. It is listed as Threatened by the state of Georgia. A total of 27 populations have been documented in 12 Coastal Plain and Fall Line counties over the last century, but most of these have not been observed in more than 25 years; of the currently known populations, only 6 are protected on conservation lands or by conservation easement.
Apply prescribed fire early in the growing season every 3 - 5 years, before plants flower. Prevent pine straw raking and other ground disturbances. Protect sandhills and scrub from development and conversion to pine plantation and agriculture.
Recent research (Wall 2012) indicates that too frequent fire has a negative impact on survival, flowering, and fruit production by this species. The researchers recommend a fire return interval no sooner than every 3 years. Fire is still recommended to reduce litter accumulation and encroachment by woody species in sandhills, both of which would have a negative effect on this species.
Chafin, L.G. 2007. Field guide to the rare plants of Georgia. State Botanical Garden of Georgia and University of Georgia Press, Athens.
GADNR. 2019. Element occurrence records for Astragalus michauxii. Georgia Department of Natural Resources, Wildlife Resources Division, Social Circle, Georgia.
Isely, D. 1990. Vascular flora of the southeastern United States, Vol. 3, Part 2, Leguminosae (Fabaceae). University of North Carolina Press, Chapel Hill.
Kunz, M., J.L Randall, J.B Gray, W.A. Wall, and M.G. Hohmann. 2016. Germination and propagation of Astragalus michauxii, a rare southeastern US endemic legume. Native Plant Journal 17:(1) 47-52. http://npj.uwpress.org/content/17/1/47.short
NatureServe. 2019. Astragalus michauxii comprehensive report. NatureServe Explorer. Arlington, Virginia. Accessed 6 January 2020. http://explorer.natureserve.org/servlet/NatureServe?searchName=Astragalus%20michauxii
Radford, A.E., H.E. Ahles, and C.R. Bell. 1968. Manual of the vascular flora of the Carolinas. University of North Carolina Press, Chapel Hill.
Russo, M.J. 1993. Astragalus michauxii element stewardship abstract. The Nature Conservancy, Arlington, Virginia.
Scimeca, M. Toxicology of the Astragalus genus. http://www.ansci.cornell.edu/plants/locoweed/astrag1.html. Website accessed October 2007.
Sorrie, B.A. 1994. Report on herbarium records from New York Botanical Garden and Rancho Santa Ana Botanical Garden for Astragalus michauxii. Georgia Department of Natural Resources, Wildlife Conservation Division, Social Circle, Georgia.
Wall, W.A., W.A. Hoffmann, T.R. Wentworth, J.B. Gray, and M.G. Hohmann. 2012. Demographic effects of fire on two endemic plant species in the longleaf pine-wiregrass ecosystem. Plant Ecology 213: 1093-1104. https://link.springer.com/article/10.1007/s11258-012-0068-7
Wall W.A., N.A. Douglas, W.A. Hoffmann, T.R. Wentworth, J.B. Gray, Q.Y.J. Xiang, B.K. Knaus, and M.G. Hohmann. 2014. Evidence of population bottleneck in Astragalus michauxii (Fabaceae), a narrow endemic of the southeastern United States. Conservation Genetics 15:153-164. https://link.springer.com/article/10.1007/s10592-013-0527-2
Weakley, A.S. 2015. Flora of the southern and mid-Atlantic states. University of North Carolina Herbarium, Chapel Hill. http://www.herbarium.unc.edu/flora.htm
Weeks, S.C. 2004. Factors limiting growth in Astragalus michauxii (Sandhill Milk-vetch). Dissertation, North Carolina State University, Raleigh. https://repository.lib.ncsu.edu/handle/1840.16/4851
Williams, M.C., G.S. Yost, and F.R. Stermitz. 1977. Miserotoxin, a toxic compound in Astragalus michauxii. Phytochemistry 16: 1438.
Linda G. Chafin
L. Chafin, Aug. 2007: original account.
K. Owers, Jan. 2010: updated status and ranks, added pictures.
L. Chafin, Jan. 2020: updated original account.
