Hexastylis - Aristolochiaceae
Contributed by L. L. “Chick” Gaddy
Some biologists think that the birthwort family (Aristolochiaceae) represents a separate and divergent branch of the evolutionary tree of flowering plants. This family is unusual among dicots in that floral parts are arranged in multiples of sixes. Hexastylis-“six styles” in Greek-is a genus of Aristolochiaceae found in the southeastern United States. The ten species and three varieties of the “heartleaves” or “wild gingers” (no relation to true ginger) are closely related to the genus Heterotropa of Japan and China. The distribution of the genus is centered in the Piedmont of western North Carolina along the Broad River near the South Carolina-North Carolina state line. Two species in the genus-Hexastylis naniflora and Hexastylis rhombiformis-are endemic to North and South Carolina; Hexastylis lewisii is found only in North Carolina and Virginia; and Hexastylis speciosa is found only in Alabama.
Hexastylis naniflora (dwarf-flowered heartleaf) is listed as threatened by the Fish and Wildlife Service. It has spring flowers less than one inch long that are usually buried in leaf litter and difficult to find. It was originally described from Cherokee County, South Carolina along a boggy, acidic stream bank in the Piedmont. At one time, the species was thought to occur in Virginia, but research over the last 20 years has located the plant in only a few counties in the upper Piedmont of North Carolina and South Carolina. Here, the heartleaf grows on Pacolet sandy loams and related soils, soils that are sandy and well-drained and lacking the red clay usually seen in the Piedmont. It is a plant of forested ravines, streamhead bogs, and mountain laurel (Kalmia latifolia) bluffs. In counties such as Spartanburg in South Carolina and Cleveland in North Carolina, it is locally common, forming large populations. Interestingly, however, if one goes north or south just a few miles, the plant does not occur. It is replaced by another Hexastylis on the Blue Ridge escarpment and inexplicably disappears in southern Spartanburg County.
It appears that Hexastylis naniflora and Hexastylis lewisii, both narrow Piedmont endemics, are sibling species of the more widespread Hexastylis heterophylla. Most Hexastylis species appear to be made up of outcrossing and selfing races (selfing plants are self pollinating or pollinate only within a small population). It is possible that selfing populations of H. heterophylla became isolated on “islands” on atypical Piedmont soils and gradually became unable to reproduce with H. heterophylla and, therefore, became H. naniflora.
When it became evident that dwarf-flowered heartleaf was a narrow endemic and was being impacted by rapid development of the upper Piedmont, the Fish and Wildlife Service listed the species as threatened. Further information on the taxonomy and distribution of the genus Hexastylis will be mailed to any interested parties if a self addressed stamped envelope is sent to: L. L. Gaddy, 125 South Edisto Avenue, Columbia, South Carolina 29205.
Editor’s Note: Dr L. L. (Chick) Gaddy is a consulting biologist who lives in Columbia and Walhalla SC. He has published numerous articles in the fields of botany, invertebrate zoology, and plant ecology, including detailed studies on the various species of heartleaf (wild ginger). He recently authored the book A Naturalist's Guide To The Southern Blue Ridge Front (USC Press, 2000).