Pyne's Ground-plum

Astragalus bibullatus

Description

Pyne's, or Guthrie's, ground-plum is a perennial member of the pea family that is known only from Rutherford County in Tennessee's Central Basin. The plant has short stems 2 in (5 cm) to 6 in (15.2 cm) long that arise from a tap root. Each stem supports five to 10 leaves. The leaves are 2 in (5 cm) to 4 in (10 cm) long and are composed of about 24 small leaflets. The inflorescence is a raceme supporting 10-16 purple flowers. The plants flower in April and May. During flowering, the peduncle supporting the inflorescence arches upward. After flowering and as the fruits mature, this peduncle gradually arches down. The fruits are fleshy pods that usually mature in May and June. At maturity the pods are colored red above and yellow below. Pyne's ground plum superficially resembles the widespread Astragalus tennesseensis (Tennessee ground-plum). However, the Tennessee ground-plum can be readily distinguished by its yellow rather than purple flowers, its yellow-brown rather than reddish topped fruits, and the copious number of hairs found on the plant.

Habitat

Pyne's ground-plum is endemic to the cedar glades of middle Tennessee. All sites are associated with thin-bedded, fossiliferous Lebanon limestone outcroppings that support the unique cedar glade communities found in Tennessee's central basin. The species only grows along the deeper soiled glade margins or in areas within the glades that are partially shaded. Soil depths vary between 2 in (5 cm) and 8 in (20 cm) at the known sites. Cedar glades are typically wet in winter and spring, and dry and very hot in summer and fall.

Distribution

There are three known populations of Pyne's ground-plum. The first colony consists of two colonies. In 1988, the first colony contained 171 plants on a 1.5-acre (0.6-hectare) glade. The site is in private ownership and is not formally protected. The second colony occurs along one edge of a privately owned residential lot located about 0.25 mi (0.4 km) from the first colony. In 1990, the site supported about 50 plants. Twenty-five of these occurred within a 100-sq ft (9.3-sq m) area, while the remaining plants were scattered along a road that crosses the site.

In addition to these two colonies, there is a group of about 100 plants on a glade located approximately 1 mi (0.6 km) northwest of the first colony. The owner of this site is a wildflower enthusiast and is believed to have established this colony with seeds collected from the nearby natural population.

The second population is located about 12 mi (19.3 km) from the first population. The site is privately owned and appears to support a declining population of Pyne's ground-plum. In 1984, several dozen plants were observed by biologists from the Department. In 1988, only five plants were observed during a visit to the site by Pyne. The years between 1985 and 1988 were very dry in central Tennessee, and this may account for the observed decline in the second population.

The third population is located about 1 mi (0.6 km) south of the first population. It was discovered in the spring of 1990 by the Tennessee Department of Conservation. Subsequent visits to the site by the Department's botanists revealed the presence of two colonies in this population. The first colony contains about 40 plants while the second colony contains about 200 plants. The 240 plants in the third population make it the largest known for Pyne's ground-plum. Additionally, Somers (in litt., 1990) describes the glades at this site as pristine.

There are believed to be two extirpated populations of Pyne's ground-plum. The first was in Rutherford County and is represented by material collected near the La Vergne railroad station in 1901 by Augustin Gattinger. The landscape in this area has been radically changed since 1901, and it is unlikely that the species still survives at this location.

Another population is believed to have been extirpated from Davidson County, Tennessee. Vegetative material that was collected in 1948 from a site just north of the Rutherford/Davidson County line by botanists from the University of Tennessee at Knoxville has been identified by Barneby as Pyne's ground-plum. The site from which the plant was collected is now under the waters of Percy Priest Reservoir. An examination of the glades adjacent to this part of the reservoir revealed that they were badly abused by vehicle travel. Pyne's ground-plum was not found in this area, and it is unlikely that the species still exists in Davidson County.

Threats

The three known naturally occurring populations of Pyne's ground plum are within a short distance of the rapidly growing middle Tennessee city of Murfreesboro. Residential, commercial, and industrial development associated with this growth threaten to destroy or adversely modify the remaining habitat for the species. All of the known ground plum locations are threatened by the encroachment of more competitive herbaceous vegetation and/or woody plants, such as cedar, that produce shade and compete for limited water and nutrients. Active management to reduce or eliminate this encroachment is required to ensure that the species continues to survive at all sites. The species is vulnerable to livestock grazing, and this factor is a threat to all populations. Direct destruction of habitat for commercial, residential, or industrial development; intensive right-of-way maintenance activities; off-road vehicle traffic; and trash dumping are the most significant threats to the species at this time (Somers and Gunn 1990, Horn, in litt., 1990).

The only other additional factor that threatens Pyne's ground-plum is the extended drought condition that the species faced through the fall of 1988. This extremely dry weather may be responsible for the decline observed in the second population and may have adversely affected the other populations. These conditions probably caused higher than normal mortality of mature plants and seedlings and could, if they had continued to the present time, have had an adverse effect on the survival of Pyne's ground-plum.

Conservation and Recovery

In order to prevent the extinction of this species the following recovery actions must be taken: 1) determine the relative importance of all known populations; 2) provide protection needed to ensure survival of populations determined to be essential to recovery of the species; 3) provide the management needed to ensure survival of species; 4) enforce laws prohibiting inappropriate trade and taking; and, 5) protect genetic material through cultivation and seed banks.

Implementation of needed recovery actions will require research that: 1) determines the habitat requirements of the species; 2) determines the biology and life history of the species; 3) determines the appropriate means of maintaining the species habitat in a manner conducive to its survival; 4) develops the techniques needed to reestablish the species at sites from which it has been extirpated.

Contacts

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
http://southeast.fws.gov/

U. S. Fish and Wildlife Service
330 Ridgefield Court
Asheville, North Carolina 28806
Telephone: (704) 665-1195, ext. 224

References

Barneby, R.C., and E.L. Bridges. 1987. "A New Species of Astragalus (Fabaceae) from Tennessee's Central Basin." Brittonia 39(3): 358-363.

Quarterman, Elsie. 1986. "Biota, Ecology, and Ecological History of Cedar Glades: Introduction." ASB Bulletin 33(4): 124-127.

Somers, Paul, and Scott C. Gunn. 1990. "Status Report Astragalus bibullatus Barneby and Bridges." Unpublished report to the Southeast Region, U. S. Fish and Wildlife Service. 33 pp.

U. S. Fish and Wildlife Service. 26 September 1991. "Determination of Pyne's (=Guthrie's) Ground Plum, Astragalus bibullatus, as Endangered." Federal Register 56.