Pyne’s ground plum  (Astragalus bibullatus)

Classified as Endangered on the IUCN Red List of Threatened Plants 1997 (1) and listed as Endangered on the U.S. Endangered Species Act 1967 (3).

Pyne’s ground plum is a rare endemic of Tennessee’s Central Basin (2), and gets its common name from Milo Pyne, who discovered the species in the 1980's, and its smooth, plum-shaped fruits that ripen on the ground (4) (5). While the stems of this plant are upright at the time of flowering, they begin to droop as the fruit develops, so that the fleshy pods are resting on the ground as they mature (4) (5) (6). Showy purple flowers are produced in early spring, followed by fruits in early summer, which, when mature, are reddish above and yellow below (2) (5). Each stem also supports five to ten green leaves that are composed of around 24 small leaflets (2).

Known only from three natural locations, and a recently introduced fourth location, within Rutherford County in Tennessee's Central Basin, U.S. (2) (5) (6).

Endemic to the cedar glades of Middle Tennessee. These glades occur on rocky limestone outcrops with exposed bedrock or very shallow soil, where trees are largely unable to grow. Pyne’s ground plum grows along the deeper soiled glade margins or in partially-shaded areas (2).

Relatively little is known about this plant’s biology and life cycle (7), other than that the flowers blossom in April and May, and the fruits mature during May and June (2).

All three naturally occurring populations are close to the rapidly growing city of Murfreesboro. Thus, associated residential, commercial and industrial development threatens to destroy or degrade the remaining habitat within the species’ already small range. Off-road vehicle traffic and refuse dumping also pose significant threats (2). Additionally, Pyne’s ground plum is vulnerable to livestock grazing and rabbit herbivory, and also threatened by encroachment of more competitive vegetation, such as cedar (2) (4).

Of the three naturally occurring populations, one is permanently protected by the State and The Nature Conservancy; the other two occur on privately owned land, one of which is being protected by the landowner. In 2001, a significant step was made towards the recovery of Pyne’s ground plum, with the creation of a new population at Stones River National Battlefield in Murfreesboro, Tennessee, as the result of the collaborative efforts of the Tennessee Department of Environment and Conservation, Missouri Botanical Garden, U.S. Fish and Wildlife Service, and National Park Service (5). This project was only made possible once, after working with the species for a number of years, workers at the Missouri Botanical Garden established reliable protocols for propagating Pyne’s ground plum from seed (4). By 2002, many of these reintroduced plants had flowered and set seed (7). Reproduction in the wild is a major milestone in the long road to recovery for this imperilled species (7), and there are high hopes that the new population will be self-sustaining (4).

For more information on pyne’s ground plum, see:

• U.S. Fish and Wildlife Service: Division of Endangered Species:
  http://arkive-admin/www.fws.gov/cookeville/docs/endspec/pynessa.html
• Center for Plant Conservation:
  http://www.centerforplantconservation.org/Collection/CPC_ViewProfile.asp?CPCNum=8648