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Species Account: Dicerandra christmanii (Lamiaceae) Huck and Judd (Revised December 2014)

Common Name: Garrett’s mint, Lake Wales Balm

Distribution: Federally and state listed as endangered; endemic to the Lake Wales Ridge in south-central Florida. Only five populations are known, all on the western part of the central Lake Wales Ridge south and southeast of Sebring.

Habitats: Lake Wales balm is found exclusively on well-drained yellow sands (Astatula and Tavares), in Florida scrub. Populations occur in scrub dominated by oaks, especially myrtle oak, and scrub hickory. This species is not found in sandhill vegetation. It also grows well in disturbed areas on appropriate soils, including roadsides, firelane edges, and power-line right-of-ways. Studies of its microhabitat preferences confirm that it is a specialist for gaps in Florida scrub dominated by evergreen, xeromorphic oaks. Microsite occupancy decreases with litter depth, litter cover, and shade. It appears to be a narrower microsite specialist than its congener D. frutescens.

Life History: Lake Wales balm is a short-lived perennial subshrub, to about 0.5 m tall. The plants are branched at the base from a single taproot. Its vegetative appearance is similar to other Dicerandra species. There have been no direct studies on how D. christmanii responds to fire. However, based on data from D. frutescens, we believe that plants are generally killed by fire, although patchy fires may allow survival of individual plants. Population recovery from complete fires is probably via dormant seeds in a persistent soil seed bank. Seed dispersal is probably limited. Shading and application of gibberilic acid promoted seed germination in a shadehouse experiment.

Phenology: Seedlings typically germinate in the winter. Plants flower in the fall (peak in October) and fruits are also formed in the fall. Seeds and fruits disperse (probably very locally judging by D. frutescens) in the fall and winter. The basal parts of the plants are perennial and maintain leaves year-round. During the summer and fall, annual shoots with leaves are produced. Flowers and fruits appear on these shoots. The annual shoots die back each winter.

Breeding System and Pollination: The flowers of Lake Wales Balm differ from D. frutescens in the colors of the anthers (brilliant yellow vs. purple) and corolla (yellowish in bud, then cream with purple-red markings for a full day, fading overnight to white vs. fading from cream to white by afternoon in D. frutescens). Self-pollinations do produce viable, germinating seeds. Pollination has not been studied. Genetics:

Genetics: Genetic variation (studied using isozymes) is surprisingly high in the single population of D. christmanii studied. A study by the Soltis Lab at the University of Florida on all 13 taxa of Dicerandra showed that the perennial species, including D. christmanii, fell into a different clade than the annual species.

Population Dynamics: Lake Wales balm has somewhat variable population sizes. Seedling recruitment varies from year to year and survival of seedlings is often low during dry periods in late spring. Seedling microsites may require a combination of mineral soil substrates and partial shade in many years. Mortality rates are moderate and lower than D. frutescens. Spatial dynamics of Lake Wales Ridge balm are probably very subtle due to limited seed dispersal. There are likely gap-level dynamics. Limited dispersal and gap closure between fires may combine to make habitat patches smaller and more isolated between fires, and larger and more connected shortly after fire. Fire probably kills all plants directly affected by high temperatures, but patchy fires may allow survival of individual plants. Population recovery from complete fires is probably exclusively via dormant seeds in a soil seed bank.

Introductions and Augmentations: We have augmented a Dicerandra christmanii population at Flamingo Villas (2010) and introduced a new population to Carter Creek South (2012), with funding from the US Fish and Wildlife Service and in collaboration with Bok Tower Gardens. The augmentation used 4000 seeds, 160 seedlings, and 40 stem-cutting transplants placed into gaps that were recently burned or long-unburned. Seedlings had higher survival than stem-cutting transplants, but high flowering for transplants quickly translated into substantial new seedling recruitment over the next several years. The 2012 introduction used seedlings and stem-cutting transplants and manipulated watering regimes. Watering increased transplant survival. Both projects showed that augmentations and introductions can be a useful tool to increase the number and size of D. christmanii populations and aid in the species’ recovery.

Interesting Facts: The various Dicerandra species are aromatic. The chemical compounds in their tissues serve to deter herbivores. Chemical analyses of these scrub mints has resulted in the discovery of one compound previously unknown in nature. The odor of Lake Wales Ridge balm is eucalyptus-like (with essential oils different than other species of Dicerandra), in contrast to the minty odor of D. frutescens. D. christmanii was first collected in Sebring in 1948 but was not placed in D. christmanii until 1989. The five species of narrowly distributed, allopatric, perennial Dicerandra species in peninsular Florida are of biogeographic interest. They may be recently evolved (neoendemics).

Data Collected by Archbold Biological Station’s Plant Ecology Lab: Since 1994, we have collected data on individually marked plants at the USFWS’ Flamingo Villas site.

Data Availability: Not Yet.

Contact Person: Eric S. Menges.

References:

  • Deyrup, M.A. and E.S. Menges. 1997. Pollination ecology of the rare scrub mint Dicerandra frutescens (Lamiaceae). Florida Scientist 60:143-157.
  • Haller, S.J. and E.S. Menges. 2012. Habitat enhancement, assisted dispersal, and introduction of Dicerandra christmanii on Lake Wales Ridge conservation lands. Final Report to US Fish and Wildlife Service. 26 pp.
  • Huck, R.B., W.S. Judd, W.M. Whitten, J.D. Skean, Jr., R.P. Wunderlin, and K.R. Delaney. 1989. A new Dicerandra species from the Lake Wales Ridge of Florida, with a cladistic analysis and discussion of endemism. Systematic Botany 14:197-213.
  • McCormick, K.D., M.A. Deyrup, E.S. Menges, S.R. Wallace, and J. Meinwald. 1993. Relevance of chemistry to conservation of isolated populations - B the case of volatile leaf components of Dicerandra mints. Proceedings of the National Academy of Sciences 90:7701-7705.
  • Menges, E.S., P.J. McIntyre, M.S. Finer, E. Goss, and R. Yahr. 1999. Microhabitat of the narrow Florida scrub endemic Dicerandra christmanii, with comparisons to its congener D. frutescens. Journal of the Torrey Botanical Society 126:24-31.
  • Menges, E.S., R.W. Dolan, R. Yahr, and D.R. Gordon. 2001. Comparative genetics of seven plants endemic to Florida’s Lake Wales Ridge. Castanea66:98-114.
  • 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