Garrett's Mint

Dicerandra christmanii

Description

Garrett's mint, Dicerandra christmanii, is a small, fragrant shrub that reaches 19.7 in (50 cm) in height. It was originally classified as scrub mint, Dicerandra frutescens, and bears a strong resemblance to that species. It can be differentiated from the scrub mint by its scent, leaf size, and the color of its flowers. Both its floriferous and vegetative shoots are stiff and ascend from a ramose (many-branched) woody base. Its taproot is branched with extensive, spreading, fibrous roots.

The leaves of Garrett's mint are sessile and have rounded apices, cuneate bases, entire margins and glandular, pitted upper and lower surfaces. Leaves found on the determinate flowering shoots are narrowly ovate to narrowly oblong. Those that subtend the cymes (embrace the flower sprouts) are 0.08-0.3 in (2-8 mm) long and 0.02-0.07 in (0.5-1.8 mm) wide, while those that do not subtend the cymes are approximately 0.2-0.4 in (5-11 mm) long and 0.04-0.1 in (1-2.5 mm) wide. The leaves of overwintering, vegetative shoots are similarly shaped, but larger.

The inflorescence is a verticillaster (circle), with each cyme containing one to three flowers. The calyx is 0.3-0.4 in (6.5-10 mm) long, approximately 0.08 in (2 mm) wide at midpoint, and bordered with an indistinct white band. The corolla is funnel shaped and abruptly bent to about 90°. Its tube is 0.3-0.4 in (7-10 mm) long, and its limb is 0.2-0.4 in (5-10 mm) long. The corolla bud is yellow, but at maturity it is a pale cream, eventually fading to white. It has vivid purple-red markings that are often trellis-patterned on the upper lobe, with irregular spots on the three-parted lower lobe.

The flowers have four paired stamens, which are exerted slightly beyond the lower corolla lip. The filaments are white, the anther (pollen producing) sacs are brilliant yellow, and the connective is widened and may be covered with a few small reddish and yellow glands at the basal end. The pollen is white and sticky. The pistil is white and has a slender, hirtellous style. The fruit is a schizocarp (a dry compound fruit that splits at maturity) of four ovoid, smooth, brown-colored nutlets.

Garrett's mint is very similar in appearance to another Dicerandra species, scrub mint (D. frutescens ). The two species are separated using the following characteristics: 1) scrub mint has a minty aroma, whereas Garrett's mint smells of cineole (camphor); 2) the leaves of scrub mint are longer than those of Garrett's mint; 3) the anthers of scrub mint are deep purple to white in color, while the anthers of Garrett's mint are a brilliant yellow; 4) the corolla of scrub mint fades from a cream color to a white within one to three and a half hours of anthesis (period of opening a flower), while the corolla of Garrett's mint retains its cream color throughout most of the first day of anthesis; and 5) the anther connectives of scrub mint have more, and larger, glands than those of Garrett's mint.

Garrett's mint flowers from July to November, primarily in September and October. Like other Dicerandra species, it has spurred anthers which must be triggered by insects for the pollen to be released and dispersed. This pollination process occurs mainly through bee flies; few other insects visit the plant. The seeds do not have mechanisms for wind dispersal and generally fall close to the plant. Some Dicerandra species have been shown to use water as a dispersal agent, sometimes having their seeds carried by streams. However, the limited distributions of Garrett's mint, scrub mint, and D. immaculata indicate that this mechanism is not effective in South Florida. Given this limited dispersal, colonization of a newly disturbed area by Garrett's mint depends on whether or not it is present in the seedbank. The life span of seeds in the seedbank is unknown.

Garrett's mint is frequently visited by bee flies. Like other Dicerandra species, it contains essential oils which protect it from feeding. Interestingly, the chemical composition of the essential oils in Garrett's mint is much different than that of scrub mint, Lakela's mint, and long-spurred mint. This explains the distinct difference in odor between Garrett's mint and the other Dicerandra species. Though not observed, Garrett's mint may be susceptible to feeding by Pyralid moths. These are the only insects known to feed on scrub mint, so they may be consumers of Garrett's mint as well.

Habitat

Garrett's mint is found within openings in sclerophyllous oak scrub. As a gap species, it prefers open areas and does not grow vigorously when in shaded conditions. The species occurs on well-to excessively-drained yellow sands of Astatula and Tavares soil types and is found where the seasonal high water table is at least 3.3-6.6 ft (1-2 m) deep.

Distribution

Garrett's mint has an extremely small range in central peninsular Florida. It is known from five populations, all in Highlands County. These populations are located between Lake Jackson and Lake Istokpoga, 6.5 mi (10.5 km) north of the range of D. frutescens. Interestingly, a slight break in the ridge occurs between the ranges of the two species at Josephine Creek.

Threats

Although habitat loss is the primary threat to Garrett's mint, there are other factors that endanger its survival. The suppression of fire has limited the number of clearings available for the growth of gap species like Garrett's mint. Also, dumping of trash and off-road vehicular traffic has resulted in erosion of habitat and trampling of individuals. This is of particular concern at Flamingo Villas, where management of the property is urgently needed to combat to rapidly increasing off-road vehicle use and trash dumping.

Conservation and Recovery

The principal site for Garrett's mint is Flamingo Villas, an unbuilt subdivision adjacent to Sebring Airport. At present, it is the only protected site for the species, and the remaining lots in the area are the highest priority for acquisition by the Lake Wales Ridge National Wildlife Refuge.

No research has been conducted on the response of Garrett's mint to management practices. However, research on this subject has been completed for scrub mint, and Garrett's mint is likely to respond in a similar manner. Therefore, this research can serve as a guideline for management of Garrett's mint.

Based on the response of scrub mint, Garrett's mint should require a burning or alternative disturbance regime to maintain the quality of its habitat. In addition, fencing of sites is needed to protect the habitat from trash dumping and off-road vehicle-induced erosion. Garrett's mint is vulnerable to trampling and vehicular traffic and is adversely affected by such impacts.

Archbold Biological Station is investigating the breeding system, pollinators, demographic patterns, and genetic variability of Garrett's mint.

Contacts

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
(404) 679-4000
http://southeast.fws.gov/

Jacksonville Ecological Services Field Office
Peninsular Florida
6620 Southpoint Dr. S., Suite 310
Jacksonville, Florida 32216-0958
Telephone: (904) 232-2580
Fax: (904) 232-2404
http://www.fws.gov/r4jafl/

Reference

Cramer, Berlin, R. B. Huck, W. S. Judd, W. M. Whitten, J. D. Skean Jr., R. P. Wunderlin, and K. R. Delaney. 1989. "A New Dicerandra from the Lake Wales Ridge of Florida, with a cladistic analysis and discussion of endemism." Systematic Botany 14 (2): 197-213.