White Irisette

Sisyrinchium dichotomum

Description

This perennial herb grows in a dichotomously-branching pattern, reaching heights of approximately 4.4-8 in (11-20 cm). The basal leaves, usually pale to bluish green, are from one-third to one-half the height of the plant. The tiny white flowers appear from late May through July in clusters of four to six at the ends of winged stems. The fruit is a round, pale to medium brown capsule containing three to six round or elliptical black seeds. The dichotomous branching pattern and white flowers combine to distinguish this herb from other species within the genus.

Habitat

This species occurs on rich, basic soils probably weathered from amphibolite. It grows in clearings and the edges of upland woods where the canopy is thin and often where down-slope runoff has removed much of the deep litter layer ordinarily present on these sites. The irisette is dependent on some form of disturbance to maintain the open quality of its habitat. Currently, artificial disturbances, such as power line and road right-of-way maintenance, where they are accomplished without herbicides and during a season that does not interfere with the reproductive cycle of this species, are maintaining some of the openings that may have been provided historically by native grazing animals and naturally occurring periodic fires.

Distribution

White irisette is endemic to the upper piedmont of North and South Carolina. It is currently known from four populations in North Carolina and one in South Carolina. The single extant site in South Carolina is in Greenville County. North Carolina's extant populations are in the following counties: Polk (six populations; Henderson (one population), and Rutherford (one population). The Greenville County, South Carolina, site is contiguous with one of the Polk County, North Carolina, sites. This species has apparently always been a narrow endemic, limited to an area in the Carolinas bounded by White Oak Mountain, Sugerloaf Mountain, Chimney Rock, and Melrose Mountain. Two of the remaining populations are within highway rights-of-way and a third is inside a commercial recreation area.

Threats

Most of the remaining populations are located in close proximity to roads or utility line rights-ofway, where they are vulnerable to extirpation from maintenance and improvement activities. Some of these populations are threatened by residential development. The species is also apparently dependent upon some form of natural disturbance. Fire suppression and the elimination of large native grazing animals from this area have altered and eliminated habitat where this species grows and may comtinue to threaten its existence. Agressive exotic weeds, such as Kudzu, Japanese honeysuckle, and Microstegium vimineum are also invading several populations.

Conservation and Recovery

The owner of one site has registered it for preservation with the North Carolina Natural Heritage Program. The Fish and Wildlife Service is working with the North Carolina Department of Transportation to protect these plants within the rights-of-way of state roads. Private landowners have been contacted regarding the presence of the plant on their property and the need to maintain the open quality of its habitat. Collection and storage of seeds and plant material has begun in cooperation with the Center for Plant Conservation and the North Carolina Arboretum.

Contact

U.S. Fish and Wildlife Service
Division of Endangered Species
1875 Century Boulevard, Suite 200
Atlanta, Georgia 30345-3319
Telephone: (404) 679-4159
Fax: (404) 679-1111

References

Bicknell, E. "Studies in Sisyrinchium (Iridaceae) in the Southeastern United States." Bulletin of the Torrey Botanical Club 26:605-616.

Hornberger, K. 1987. Systematics of the genus Sisyrinchium (Iridaceae) in the Southeastern United States. Unpublished Ph.D. dissertation, University of Arkansas. 328 pp.

U.S. Fish and Wildlife Service. 26 September 1991. "Determination of Endangered Status for White Irisette, Sisyrinchium dichotomum." Federal Register.