Upland Pine, Blackwater River State Forest. Photo by Gary Knight

Monday, January 22, 2018

Update from the Field: FNAI Scientists Document Additional Populations of a Rare Mint

Longspurred mint plant. Photo by Brenda Herring
Longpsurred mint flower. Photo by Katy NeSmith

This fall FNAI field scientists conducted surveys for the federally endangered and Florida-endemic longspurred mint (Dicerandra cornutissima) in hopes of assessing its status, threats, range, and population size for the U.S. Fish and Wildlife Service.  Prior to this survey, longspurred mint was ranked G1 (critically imperiled globally) by FNAI.  It closely resembles the other mint species (Dicerandra spp.) in Florida, however, major differences can be found in their flowering phenology, morphology and geographical location. Longspurred mint usually flowers in September to October, which is the shortest flowering season of the mints. The longspurred mint, only known from Marion and Sumter counties, has no geographical overlap with the other rare mints. It favors open areas within scrub and sandhill, two imperiled natural communities in Florida.

Longspurred mint flower. Photo by Katy NeSmith.

Longspurred mint in a sandhill habitat. Photo by Brenda Herring.
Known extant and historical populations were checked and updated and field scientists searched in promising new areas for the mint.  The Marjorie Harris Carr Cross Florida Greenway, in Marion County, remains the stronghold of the mint population, where many new populations were documented. A nearby stretch of Interstate 75 continues to have a good number of plants on the upper shoulders of the lanes. Adjacent neighborhoods to the north and south of the Greenway also harbor an abundance of plants along roadsides and edges of undeveloped lots. Sumter County surveys did not locate any new populations, but did reconfirm one old record, making it the only known location in the county. Garberia (Garberia heterophylla), a state listed endemic plant was often found with the longspurred mint. Other, not-so-desirable, associates include invasive exotic plants that were occasionally found with the mint, especially cogon grass (Imperata cylindrica) and natal grass (Melinis repens).

Cogon grass. Photo by Brenda Herring.
These findings led to a change in the FNAI rank of the longspurred mint from G1 to G2 (imperiled globally), a proposed monitoring protocol, and several proposed research and management needs. The effect of prescribed fire and other management activities (e.g., logging, creating fire lines) on the mint is not well understood and warrants study.  Exploring additional methods to control exotic plant competitors is also of interest. We hope that our information can be used to help monitor, manage, and protect one of Florida’s most beautiful endemic species.  This study is an excellent example of how FNAI field surveys help refine our understanding of conservation needs for Florida’s rare species.