Pyne's Ground Plum

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).

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).

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).

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).

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).

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).

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).

Perennial, Herbs, Stems woody below, or from woody crown or caudex, Taproot present, Nodules present, Stems or branches arching, spreading or decumbent, Stems less than 1 m tall, Stems solid, Stems or young twigs glabrous or sparsely glabrate, Stems or young twigs sparsely to densely hairy, Leaves alternate, Leaves petiolate, Stipules cons picuous, Stipules green, triangulate to lanceolate or foliaceous, Stipules membranous or chartaceous, Stipules persistent, Stipules free, Stipules connate to each other, forming a tuber or sheath, Leaves compound, Leaves odd pinnate, Leaf or leaflet margins entire, Leaflets opposite, Leaflets 10-many, Leaves hairy on one or both surfaces, Inflorescences racemes, Inflorescence axillary, Bracts very small, absent or caducous, Flowers zygomorphic, Calyx 5-lobed, Calyx hairy, Petals separate, Corolla papilionaceous, Petals clawed, Petals blue, lavander to purple, or violet, Banner petal narrow or oblanceolate, Wing petals narrow, oblanceolate to oblong, Wing tips obtuse or rounded, Keel petals auriculate, spurred, or gibbous, Keel tips obtuse or rounded, not beaked, Stamens 9-10, Stamens diadelphous, 9 united, 1 free, Filaments glabrous, Style terete, Style persistent in fruit, Fruit a legume, Fruit humistrate, lying on the ground, Fruit indehiscent, Fruit elongate, straight, Fr uit oblong or ellipsoidal, Fruit orbicular to subglobose, Fruit or valves persistent on stem, Fruit exserted from calyx, Fruit inflated or turgid, Fruit beaked, Fruit glabrous or glabrate, Fruit 11-many seeded, Seeds cordiform, mit-shaped, notched at one end, Seed surface smooth, Seeds olive, brown, or black.

Pyne's ground plum (fruits) Close-up of the flowers

Astragalus bibullatus, the limestone glade milkvetch or Pyne's ground plum, is an endangered species of flowering plant that is endemic to the cedar glades of the central basin of Tennessee in the United States. It is found in only eight populations located within a few kilometers of each other in Rutherford County, Tennessee.