Garber's Spurge

Chamaesyce garberi

Description

Garber's spurge is a short-lived, perennial herb belonging to the Euphorbiaceae or spurge family. This species is known from pine rocklands, coastal flats, coastal grasslands, and beach ridges in Dade and Monroe Counties, Florida. It requires open sunny areas and needs periodic fires to maintain habitat suitability. It is found throughout its historic range and is abundant in some areas, but the populations are relatively disjunct. Habitat loss and exotic pest plant invasion threaten its recovery.

Garber's spurge, Chamaesyce garberi, is a prostrate to erect herb with pubescent stems. The leaves are ovate in shape and 0.2-0.4 in (5-10 mm) long, with entire, or obscurely serrate leaf margins. The cyathia is about 0.1 in (2.5 mm) long and borne singly at leaf axils. The appendages are minute or completely absent. The fruit is a pubescent capsule 0.1 in (2.5 mm) wide. The seeds either are smooth or have transverse ridges, but are not wrinkled; this is not, however, a distinctive character for this species. A. Herndon included Chamaesyce porteriana var. keyensis under Garber's spurge.

Reproductive ecology in Chamaesyce has been poorly studied, but is known to be highly variable. Some species are completely reliant on insects for pollination and seed production while others are self-pollinating. Pollinators may include bees, flies, ants, and wasps. The seed capsules of many Euphorbiaceae are explosively dehiscent, ejecting seeds a short distance from the parent plant. Some seeds are dispersed by ants.

Habitat

Garber's spurge occurs at low elevations either on thin sandy soils composed largely of Pamlico sands or directly on limestone. It is found in a variety of open to moderately shaded habitat types. In pine rocklands, it grows out of crevices in oolitic limestone. On Cape Sable, Everglades National Park, it has been reported from hammock edges, open grassy prairie, and backdune swales. In the Florida Keys, it grows on semi-exposed limestone shores, open calcareous salt flats, pine rocklands, calcareous sands of beach ridges, and along disturbed roadsides.

Distribution

Garber's spurge is endemic to South Florida. It is abundant on Cape Sable and is probably found throughout the Keys in small numbers. Historically, it occurred from Perrine, Dade County, west to Cape Sable, Monroe County, and to the sand keys west of Key West, Monroe County. A complete status survey has not been performed for the Garber's spurge since 1980. At that time, five sites were identified; three on Cape Sable (Everglades National Park), one on Long Pine Key (Everglades National Park), and one on Big Pine Key. Only the Long Pine Key site has been resurveyed, and it was found to contain approximately 150 plants. Cape Sable, in Everglades NP, has an invasive exotics problem, which the Park was not able to address for some time. The extent of the exotic plant cover was partially assessed in 1996; an exotics' control program was anticipated for 1997. The status of the three Garber's spurge populations on the cape is not known. A new population was found in 1988 at the Charles Deering Estate, Dade County, after a burn. It had 250-500 plants in 1991, but the population size appears to be getting smaller. Since Herndon's inclusion of C. porteriana, two other sites have been added, Bahia Honda State Park and Long Key State Recreation Area. The population sizes and trends at these sites are unknown.

Threats

Habitat for the Garber's spurge has been lost to development, fire suppression, and invasive exotics. In addition, the remaining habitat is relatively fragmented and most populations are small. These small, disjunct populations are more susceptible to extirpation from a single disturbance, natural or man-made, without the chance of recruitment from a nearby population. Fire suppression and the invasion of exotic plants can result in overshading of the understory, reducing the quality of the habitat. Over time this could lead to the extirpation of Garber's spurge.

Conservation and Recovery

Garber's spurge occurs in a few protected areas where it is being managed. The National Key Deer Refuge uses prescribed fire to manage pineland habitats on the refuge. The main focus of their management is for the Key deer, but it may benefit Garber's spurge. In Everglades NP, fire is used as a management tool in pine rocklands. However, management at Cape Sable has been limited by lack of available manpower and funding.

Garber's spurge occurs in a variety of habitats in the Florida Keys and Dade County and will require management practices specific to each habitat. Although there are differences between the habitats, they are all early successional and require some type of disturbance, such as fire or wash over. The habitats in the Florida Keys have a slower growth rate than similar habitats in Dade County and require less frequent disturbance.

Presently, many of the publicly owned lands in the Florida Keys, and Everglades NP use prescribed fire as a management tool. Fire management in Everglades National Park has shifted to an early wet season burn schedule. In Dade County pinelands, a fire frequency of three to seven years is generally recommended. However, in the Florida Keys there is very little information available to determine how frequently disturbances are needed. Any prescribed fire management, especially in the Florida Keys, should include a monitoring program to determine the effectiveness of management.

Invasive exotic plant species, especially Brazilian pepper and Burma reed, threaten many of the pine rockland species and other rare pine rockland plants. The control of exotic species is a very important part of maintaining the habitat although it can be very costly once exotics are established in an area. The Florida Keys Invasive Exotics Task Force had organized a mapping project where about 25 people mapped exotic species from Key West to Key Largo. The group used aerial photographs to map the distribution and degree of infestation of Australian pine, Brazilian pepper, and Asiatic colubrina and noted Burma reed and melaleuca on the roaded islands from Key West to North Key Largo. This information will give a better understanding of the degree of infestation and help identify areas of high priority for exotics' control.

Contact

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

References

Burch, D. 1966. "Two New Species of Chamaesyce: New Combinations and a Key to the Caribbean Members of the Genus." Annals of the Missouri Botanical Garden 53: 90-99.

Shaw, C. 1975. "The Pine and Hammock Forest-lands of Dade County." Report to Dade County, Florida, County Manager.

Ward, D. B. 1979. Rare and Endangered Biota of Florida. Vol. 5, Plants. University Presses of Florida, Gainesville.