Tephrosia virginiana (L.) Pers.
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Basis for Listing
Tephrosia virginiana is found throughout the eastern United States except for Maine and Vermont, and also occurs in Ontario, Canada. It reaches the northwest limit of its range in southeast Minnesota where it occurs in just four counties, all within the Blufflands Ecological Subsection. Tephrosia virginiana is typically found on deep sand and gravel deposits along several major rivers in the southeast including the Root, Whitewater, Mississippi, and Zumbro rivers. All historic occurrences of the species are also from these areas.
Tephrosia virginiana is a perennial legume with one to several stems branching from the base of the plant. It is 20-70 cm (7.9-27.6 in.) tall and has a soft, gray-green appearance due to the presence of many silky hairs on its leaves and stems. It has two-toned pink and cream flowers that are 1.5-2.0 cm (0.59-0.75 in.) across. Flowers are arranged in dense clusters at the tips of the stems. The fruit is a long, narrow, hairy pod (Black and Judziewicz 2008) up to 5 cm (2.0 in.) long (Ladd 1995). Each leaf is pinnately divided into 15-31 narrowly oval-shaped leaflets.
In Minnesota, T. virginiana most often grows in dry, sandy habitats with lots of sunlight and scattered trees. It is found in denser woodland settings as well, but mostly in the sunny openings between groups of trees. Vegetation in these habitats is typically sparse, with bare ground between plants. Tephrosia virginiana often grows on south- and west-facing slopes, although it can be found in level habitats on sand as well. All of the habitats are fire-dependent and found on very well-drained deep sands or sand and gravel. The most common canopy tree associated with T. virginiana is Quercus velutina (black oak) although it is sometimes found with Q. ellipsoidalis (northern pin oak) or Q. macrocarpa (bur oak), and occasionally under Pinus banksiana (jack pine) or P. strobus (white pine). Other commonly associated species are Schizachyrium scoparium var. scoparium (little bluestem), Monarda punctata var. villicaulis (horsemint), Lupinus perennis (wild lupine), and Tradescantia spp. (spiderworts).
Biology / Life History
Tephrosia virginiana is an insect pollinated species. The seeds are dispersed short distances when the pods break open and twist, throwing the seeds. Tephrosia virginiana has deep woody roots, which contain rotenone, a fish poison (Great Plains Flora Association 1986).
Conservation / Management
The prairie and savanna habitats of T. virginiana were originally maintained by frequent wildfires, but active fire suppression has interrupted this cycle. When woody species close in and increase the amount of shade in the habitat, T. virginiana decreases in number or disappears. Therefore, it is important to use prescribed fire to manage the habitat of this species. Other threats include invasion of non-native species, livestock grazing, and off-road vehicles. Invasive species such as Centaurea maculosa (spotted knapweed) and Euphorbia esula (leafy spurge) are chronic problems in sandy prairies in southeast Minnesota where they are able to outcompete native vegetation for light, space, nutrients, and/or water. Tephrosia virginiana is also known to disappear with grazing (Great Plains Flora Association 1986). Lastly, off-road vehicle use easily disturbs unstable sandy soils and associated vegetation, and makes the site vulnerable to erosion. This can contribute to loss of habitat for T. virginiana, or may directly impact individual plants.
Conservation Efforts in Minnesota
Most existing populations of T. virginiana are located on public lands, including three Scientific and Natural Areas (Rushford Sand Barrens SNA, Mound Prairie SNA, and Kellogg-Weaver Dunes SNA). A large complex of populations is also located in the Whitewater Wildlife Management Area along the Whitewater River, and several populations are within the R.J. Dorer Memorial State Forest. Some of these areas are likely managed with fire, but it is unknown whether specific management efforts have been targeted at this rare species.
Black, M. R., and E. J. Judziewicz. 2008. Wildflowers of Wisconsin and the Upper Midwest. Cornerstone Press, University of Wisconsin, Stevens Point, Wisconsin. 271 pp.
Dudley, J. L., and K. Lajtha. 1993. The effects of prescribed burning on nutrient availability and primary production in sandplain grasslands. American Midland Naturalist 130(2):286-298.
Gleason, H. A., and A. Cronquist. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. Second Edition. New York Botanical Garden, Bronx, New York. 910 pp.
Great Plains Flora Association. 1986. Flora of the Great Plains. University Press of Kansas, Lawrence, Kansas. 1,402 pp.
Ladd, D. M. 1995. Tallgrass prairie wildflowers: a field guide. Falcon Press Publishing Co., Inc., Helena and Billings, Montana. 262 pp.