Geocarpon minimum

No Common Name

Description

Geocarpon minimum, is an inconspicuous, succulent annual, ranging from 0.4-1.6 in (1-4 cm) in height. Stems are simple or branching near the base, rising from a slender taproot. The opposite leaves are narrowly oblong, and only about 0.2 in (4 mm) long. Tiny flowers attached at the leaf have a greenish-red calyx. The fruit capsule breaks into three parts at maturity, releasing numerous seeds. Plants are dull gray when young and turn reddish-purple at maturity. The species is ephemeral, usually completing its life cycle within about four weeks in the spring. Seeds do not germinate every year, particularly when there is low rainfall.

Habitat

G. minimum is restricted to eroded spots in grasslands called slicks or slickspots by soil scientists. Slicks are typically high in salinity and may be the remains of ancient Pleistocene lake beds. It is uncertain whether slicks are renewed in nature or whether they eventually disappear from the landscape. If slicks are renewed by fire or flooding, then G. minimum could be considered a pioneer species— one of the first plants to take root in a newly cleared habitat. It is then forced out by succeeding growth.

Distribution

G. minimum is a monotypic genus (the genus has but one species) that was first collected in 1913 in Jasper County, Missouri. The species has since disappeared from this site. The dispersal of remaining sites suggests that this plant was once found in disjunct localities throughout much of Arkansas and southern Missouri.

When listed in 1987, G. minimum was documented at 17 sites in Missouri and Arkansas, four on public lands. In Missouri, the plant was found in Dade, Polk, St. Clair, Cedar, Lawrence, and Greene counties. Only four of 13 sites there supported substantial numbers of plants. In Arkansas, four populations were known from Bradley, Cleve-land, Drew, and Franklin counties. The largest population is found in the Warren Prairie Natural Area.

By the time the U.S. Fish and Wildlife Service (FWS) produced the species' recovery plan in 1993, the FWS was reporting the existence of 27 documented sites in Arkansas, Louisiana and Missouri. Only nine of the sites (two in Arkansas, one in Louisiana, and six in Missouri) were known to support relatively large, vigorous populations.

The plant is locally abundant, numbering in the thousands, but its highly restricted distribution makes it vulnerable to extinction.

Threats

Research is ongoing, but the major threat to the species seems to be gradual loss of habitat due to vegetational succession. Where grasses or shrubs encroach upon a slick, G. minimum fails. Several former sites were cleared of native plants for use as pasture, allowing more aggressive prairie grasses to invade. In the absence of invading species, cattle grazing may actually benefit the species by maintaining bare patches of earth where seedlings can grow.

Conservation and Recovery

G. minimum is classified as an endangered plant in Arkansas and Missouri. The Missouri Department of Conservation (MDC) manages a population at the Taberville Prairie Natural Area in St. Clair County and oversees a second population at the Bona Glade Natural Area in Dade County.

In 1991, the Arkansas Natural Heritage Commission (ANHC) completed a five-year research project, funded by the FWS, the results of which have helped determine the direction of recovery efforts. The ANHC also acquired additional acreage for the Warren Prairie Natural Area in order to increase the species' protected habitat.

The 1993 recovery plan notes that the species will be considered for delisting when a total of 15 viable populations, representing the diversity of habitats and geographic range of the species, are protected as necessary to ensure their continued existence. The plan states that populations should also include the wide spectrum of current genetic variation found in this species, and that population viability should be confirmed through periodic monitoring for at least a 15-year period.

To achieve the recovery goals, the plan outlined a number of actions needed. Among them are the protection of viable populations across the species' geographic range; the evaluation of potential habitat and the search for additional populations; the continued monitoring of known sites to determine population trends; and the support of basic research to investigate the chemical characterization of the plant's substrate and species biology, dispersal ecology, and population genetics. The plan also calls for the determination of the effects of disturbance factors (both natural and human-made) and the incorporation of these findings into management prescriptions. The preservation of genetic stock is another necessary action, as is the establishment of additional populations in the Arkansas Valley Natural Division, if deemed necessary.

Contacts

Regional Office of Endangered Species
U.S. Fish and Wildlife Service
Federal Building
Ft. Snelling
Twin Cities, Minnesota 55111
http://midwest.fws.gov/

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

References

Bogle, A. L., et al. 1971. " Geocarpon: Aizonaceae or Caryophyllaceae?" Taxon 20(4):473-477.

Palmer, E. J., and J. Steyermark. 1950. "Notes on Geocarpon minimum MacKenzie." Bulletin of the Torrey Botanical Club 77:268-273.

Rettig, J. 1983. "A New Arkansas Station for Geocarpon minimum MacKenzie." Bulletin of the Torrey Botanical Club 77:268-273.

Steyermark, J., J. W. Voigt, and R. H. Mohlenbrock.1959. "Present Biological Status of Geocarpon minimum MacKenzie." Bulletin of the Torrey Botanical Club 86:228-235.

U.S. Fish and Wildlife Service. 1993. " Geocarpon minimum Recovery Plan." U.S. Fish and Wildlife Service, Twin Cities, Minnesota.