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Dicerandra radfordiana R.B. Huck
Radford's Dicerandra

Dicerandra radfordiana by James Holland. Image may be subject to copyright.
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Federal Protection: No US federal protection

State Protection: Endangered

Global Rank: G1Q

State Rank: S1

Element Locations Tracked in Biotics: Yes

SWAP High Priority Species (SGCN): Yes

Element Occurrences (EOs) in Georgia: 2

Habitat Summary for element in Georgia: Sandridges


Description

Annual herb up to 26 inches (65 cm) tall, with erect, hairy stems; the base of the stem is often swollen by an insect gall. Leaves are 0.8 - 2 inches (1.9 - 55 cm) long (averaging 4 cm long) and about 0.2 inch (4 - 6 mm) wide, opposite, narrowly oblong, lacking leaf stalks, with a cluster of small leaves at the base of each larger leaf; the leaf margins are smooth or more often have small teeth; leaf surfaces have tiny, rough hairs and pitted glands that give off a cinnamon-like odor when brushed or crushed. The flower is more than 0.7 inch (2 cm) long with a narrow, straight (or slightly curved) tube that opens out into 2 lips; the upper lip is hood-like, the lower lip is divided into 3 blunt lobes and is bright pink with dark dots. Four stamens extend only slightly beyond the lips, each stamen with 2 small, curved “horns” on the anthers.

Similar Species

Rose Balm (Dicerandra odoratissima) also smells like cinnamon but is smaller than Radford’s Mint. Its leaves are narrower and more needle-like and average 1 inch (2.5 cm) long; the leaf margins are always entire. The pale pink flower tube is shorter, about 0.7 inch (1.8 cm) long.

The leaves of Coastal Plain Balm (D. linearifolia) smell like fresh mint; its flowers have a funnel-shaped, sharply bent tube less than 0.6 inch long with widely spreading lips; its stamens are showy and extend well beyond the tube and lips.

Related Rare Species

None in Georgia. Several species of Dicerandra are rare and endemic to the central peninsula of Florida.

Habitat

Lower Altamaha River bluffs with deep, well drained sands.

Life History

Radford’s Mint is an annual herb that reproduces by seed. Its flowers are probably pollinated by hawkmoths or, possibly, butterflies such as cloudless sulphur and Gulf fritillary. Flowers appear to successfully produce fruit, which are dispersed short distances when the plant is jostled by strong winds or other movement. Long-distance seed dispersal may occur following rainstorms that move the buoyant, mucilage-coated fruits into the nearby Altamaha River. The strong odor given off by the glands that cover the leaf surfaces deters insects and other animals from eating the leaves.

Survey Recommendations

Surveys are best conducted during flowering (late September–late October).

Range

Found only in McIntosh County, Georgia.

Threats

Conversion of habitat to development, pasture, or pine plantations; sand mining.

Georgia Conservation Status

Dicerandra radfordiana is ranked S1 by the Georgia Department of Natural Resources, indicating that the species is critically imperiled in Georgia. It is listed as Endangered by the State of Georgia. Only 2 populations are known; one occurs on a state wildlife management area; another, on private land, is protected by a conservation easement. Size of populations varies widely from year to year, depending on summer rainfall.

Conservation Management Recommendations

Although plants are adapted to occasional disturbance, avoid clearcutting (unless part of an ecological restoration plan), sand mining, and other severe disturbances. Use prescribed fire to create sunny openings and control woody species.

References

Allison, J.R. 1993. Status survey of Dicerandra radfordiana Huck, Radford dicerandra. Georgia Department of Natural Resources, Wildlife Resources Division, Social Circle.

Chafin, L.G. 2007. Field guide to the rare plants of Georgia. State Botanical Garden of Georgia and University of Georgia Press, Athens.

GADNR. 2020. Element occurrence records for Dicerandra radfordiana. Georgia Department of Natural Resources, Wildlife Resources Division, Social Circle, Georgia.

Huck, R.B. 1981. Dicerandra radfordiana, a new labiate from Georgia. Phytologia 48(6): 433-436.

Huck, R.B. 1987. Systematics and evolution of Dicerandra (Labiatae).  Phanerogamarum Monographiae Volume 19: 1 - 344. https://www.schweizerbart.de/publications/detail/isbn/9783443780012/%23

NatureServe. 2019. Dicerandra radfordiana comprehensive report. NatureServe Explorer. Arlington, Virginia. http://explorer.natureserve.org/servlet/NatureServe?searchName=Dicerandra%20radfordiana

Oliveira, L.O, R.B. Huck, M.A. Gitzendanner, W.S. Judd, D.E. Soltis, and P.S. Soltis. 2007. Molecular phylogeny, biogeography, and systematics of Dicerandra (Lamiaceae), a genus endemic to the southeastern United States. American Journal of Botany 94: 1017-1027. https://bsapubs.onlinelibrary.wiley.com/doi/abs/10.3732/ajb.94.6.1017

Payton, A. C., A. A. Naranjo, W. Judd, M. Gitzendanner, P. S. Soltis, and D. E. Soltis. 2019. Population genetics, speciation, and hybridization in Dicerandra (Lamiaceae), a North American Coastal Plain endemic, and implications for conservation. Conservation Genetics 20(3): 531-543. https://link.springer.com/article/10.1007/s10592-019-01154-8

Weakley, A.S. 2007. Flora of the Carolinas, Virginia, Georgia, and surrounding areas. University of North Carolina Herbarium, Chapel Hill. http://www.herbarium.unc.edu/flora.htm

Authors of Account

Linda G. Chafin

Date Compiled or Updated

L. Chafin, Feb. 2007: original account.

K. Owers, Jan. 2010: updated status and ranks, added pictures.

L. Chafin, Feb 2020: updated original account.

Dicerandra radfordiana illustration by Jean C. Putnam Hancock. Image may be subject to copyright.
Dicerandra radfordiana by Hugh and Carol Nourse. Image may be subject to copyright.
Dicerandra radfordiana by Hugh and Carol Nourse. Image may be subject to copyright.
Dicerandra radfordiana, early summer aspect, by James Holland. Image may be subject to copyright.
Dicerandra radfordiana, late fall aspect, by Alan Cressler. Image may be subject to copyright.