CPC Plant Profile: Pyne's Ground-plum
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Plant Profile

Pyne's Ground-plum (Astragalus bibullatus)

Purple-pink flowers appear in April and May. Photo Credit: Rebecca Sucher
  • Global Rank: G1 - Critically Imperiled
  • Legal Status: Federally Endangered
  • Family: Fabaceae
  • State: TN
  • Nature Serve ID: 143330
  • Date Inducted in National Collection: 03/05/1993

Pyne's ground-plum is a beautiful legume that is endemic to the Central Basin of Tennessee. First described in 1987, the plant is found only in a cedar glade habitat (Barneby and Bridges 1987). The ground-plum gets its name from the fruits produced in late May to early June. While the lavender flowers are borne on upright stalks, as the fruits develop the stalks bend back towards the ground. The fruits turn a reddish orange color and appear larger than one would expect, given the overall size of the plant.

Participating Institutions
Center for Plant Conservation
  • 10/27/2021
  • Reintroduction

In 2008 a report was made on an introduction within a historic range. This project was an introduction to a new site within the known range of Astragalus bibullatus. The factors transplant season and population propagule source were tested experimentally to determine their effects on transplant success at the new site over a six-year period. Seed was collected from three source populations and then propagated in the greenhouse. One-year old seedlings were outplanted at five nearby sites, simulating a metapopulation structure. The effects of population source were not significant at the new site. Plants introduced in the fall exhibited greater survival and transitional probabilities into reproductive adults than plants introduced in the spring. Despite the seemingly apparent suitability in habitat, the effects of glade site were the most important factor explaining transplant survival. In the first three years following outplanting, transition probabilities into reproductive adults were similar to wild populations. However, the last four years of the introduction, no individuals sexually reproduced and only one seedling recruit was observed in the population.

Center for Plant Conservation
  • 08/17/2021
  • Orthodox Seed Banking

In 2021, CPC contracted the Missouri Botanical Garden to recollect seed from a population currently held in long term orthodox seed storage as part of an IMLS-funded seed longevity experiment. The National Laboratory for Genetic Resources Preservation will evaluate how germination tested viability and RNA Integrity of seed lots decline over time in storage.

  • 08/26/2020
  • Propagation Research

Workers at Missouri Botanical Garden have been working with this species for a number of years, and have established reliable protocols for propagating A. bibullatus from seed. (McCue et al. 2001)

  • 08/20/2020
  • Seed Collection

Maintain seed collections. Plants grown from wild collected seed were transplanted into secure habitat in Rutherford County during different times of the year.

Nature Serve Biotics
  • 05/02/2017

Endemic to Tennessee's Central Basin where it is known from three extant populations. One population on private land is threatened with destruction and two historic populations are believed extirpated. The plant requires active management to limit encroachment of more competitive plants. Limestone glades in the Central Basin are located in the Metropolitan Nashville area and are rapidly being developed.

Kimberlie McCue, Ph.D.
  • 01/01/2010

Primary threats include residential or commercial development, possible loss of pollinators, livestock grazing, and encroachment of more competitive vegetation (USFWS 1991). Rabbit herbivory and all-terrain vehicles (ATV's) also pose significant threat

Kimberlie McCue, Ph.D.
  • 01/01/2010

There are three known wild populations (USFWS 1991).

Kimberlie McCue, Ph.D.
  • 01/01/2010
  • Genetic Research

Population genetic studies have determined that populations of the ground plum are very similar (Baskauf and Snapp 1998). Workers at Missouri Botanical Garden have been working with this species for a number of years, and have established reliable protocols for propagating A. bibullatus from seed. (McCue et al. 2001) Genetic studies using allozymes demonstrated that higher genetic diversity is found in the resident seed bank for this population than in vegetative populations, and determined that seeds in the uppermost layer of the seed bank showed increased inbreeding and decreased relative levels of gene flow. (Morris et al. 2002)

Kimberlie McCue, Ph.D.
  • 01/01/2010
  • Reintroduction

Attempts to establish a new population of A. bibullatus began in 2001. Plants grown from wild collected seed were transplanted into secure habitat in Rutherford County during different times of the year. In 2002, plants that had been transplanted in the fall flowered, and the hopes are high that this new population will be self-sustaining. (Plant Conservation 2002) The Tennessee Department of Environment and Conservation is monitoring all known sites.

Kimberlie McCue, Ph.D.
  • 01/01/2010

Management and research needs include locating new populations, understanding reproductive biology and ecology, seedling recruitment, life history traits and habitat requirements.

Kimberlie McCue, Ph.D.
  • 01/01/2010
  • Orthodox Seed Banking

Maintain seed collections


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Taxon Astragalus bibullatus
Authority Barneby & Bridges
Family Fabaceae
CPC Number 8648
ITIS 192810
Common Names Guthrie's ground-plum | limestone glade milkvetch | Pyne's Ground Plum | Pyne's ground-plum
Associated Scientific Names Astragalus bibullatus
Distribution All known populations of A. bibullatus occur in Rutherford County, Tennessee (USFWS 1991).
State Rank
State State Rank
Tennessee S1

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 (USFWS 1991).Common associates include Juniperus virginiana, Pediomelum subacaule, Hypericum sphaerocarpum, Manfreda virginica, Glandularia canadensis, and Onosmodium molle (USFWS 1991).

Ecological Relationships

This species has a long-lived seed bank. (Morris et al. 2002)

Common Name Name in Text Association Type Source InteractionID

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