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Florida ziziphus (Ziziphus celata Judd and Hall) is one of about 20 Lake Wales Ridge plants monitored and studied by the Archbold Biological Station’s Plant Ecology Lab. Florida ziziphus is a federally-listed Lake Wales Ridge endemic, named in 1984, and rediscovered in the wild in 1987. Its story is told below in a recent article from The Palmetto, the quarterly journal of the Florida Native Plant Society.
     We are interested in communicating with other researchers working on other species of Ziziphus, especially those species occurring in the southwestern US or northern Mexico; with researchers with similar research interests (e.g., limited fecundity due to low genetic diversity); and with anyone with knowledge of additional sites for Florida ziziphus.

Ziziphus celata, Archbold Plant Lab species account

     Please contact us in any of the following ways:
Carl W. Weekley, Archbold Biological Station, Plant Ecology Lab, phone: 863-465-2571 ex 234. E-mail: weekley@archbold-station.org.
Tammera Race, Trout Lake Nature Center, P.O. Box 641, Eustis, FL 32727.

Saving Florida Ziziphus:
Recovery of a Rare Lake Wales Ridge Endemic

Carl Weekley (Archbold Biological Station),
Tammera Race (Bok Tower Gardens; now at Trout Lake Nature Center), and
Dennis Hardin (Florida Division of Forestry)

This article is reprinted, with permission, from the Florida Native Plant Society's quarterly journal, The Palmetto, Vol. 19, No. 2, Summer 1999.

Species description | Habitat and distribution | Genetics | Breeding system experiments | Ziziphus and fire | Translocation projects | Perspectives for future work

Florida ziziphus (Ziziphus celata Judd & Hall) is one of the rarest and most imperiled plants in Florida. It is known from only five sites--and perhaps as few as eleven individuals--on the Lake Wales Ridge in Polk and Highlands counties. This year is the 10th anniversary of its listing as a federally endangered species. Over the past several years, we have been working to design and implement a recovery plan to save Florida ziziphus.

Recovery of endangered plants involves many disparate (but inter-dependent) activities, including site acquisition, establishment of off-site collections in botanical gardens, research on the biology, genetics and ecology of the species, monitoring populations and the collection of demographic data, adaptive management of natural populations, and the translocation of plants to augment existing populations or to create new ones. The effort to save Florida ziziphus has required all of these activities.

Species description.  [back]   Florida ziziphus was named and described by Walter Judd and David Hall in 1984 [Rhodora 86:381-387] from a specimen, collected near Sebring in 1948, which had languished in an herbarium drawer for 36 years. When Judd and Hall published their description, they believed the plant to be extinct, but in 1987 Kris DeLaney discovered a small population just outside a state forest. Within the next few years, four additional populations were discovered, all on private land. DeLaney's original site was acquired by the state in 1995.

A member of the buckthorn family (the Rhamnaceae), Florida ziziphus is a single or multi-stemmed woody shrub, 3 to 6 ft. in height . It has spiny, zigzag branches with small (less than 1 in. long) alternate leaves, shiny on their upper surface. The leaves are deciduous, falling in November-December before flowering begins in early January. Flowers are tiny--four fit neatly on the face of a dime--and are perfect, containing five stamens and a pistil surrounded by a nectar ring.

Mature plants bloom profusely, with flowers numbering in the tens of thousands. The fragrant flowers attract legions of insects, including flower flies, bees, wasps and butterflies. Some floral visitors are quite noisy and on sunny mornings plants can be heard as well as smelled from several yards away. The fruit is a drupe about ½ in. in length which turns yellow as it ripens in late May. [see Atlas of vascular plants for photos -- click on DICOTS-P-R and scroll to Rhamnacaea, Ziziphus.]

Habitat and distribution.   [back]   Florida ziziphus is known exclusively from yellow sand sites which historically supported sandhill or oak-hickory scrub. The five known sites fall along a narrow 30-mile long axis on the eastern edge of the Lake Wales Ridge.

The only protected population is found on the state forest site, where it occurs in both turkey oak sandhill and open oak-hickory scrub in association with other federally-listed species. The only other natural site is a one-tenth acre remnant wiregrass sandhill surrounded by exotic vegetation. Three of the five populations are now in pastures, where they have been subjected to mowing, periodic (unsuccessful) attempts at eradication, and trampling by cattle.

In addition to the state forest site, we have had access to three of the privately-owned sites for monitoring, research, and various management activities including exotics removal, fencing and prescribed burning. Until recently, the fourth privately-owned site, a large pasture population consisting of hundreds of stems, had been inaccessible to us since its discovery. We refer to it below by its code name, H01.

Root cuttings from these five sites were used to propagate an off-site population in the Center for Plant Conservation National Collection at Bok Tower Gardens (BTG). This "captive" population has been important because it has provided our only access to sexually-reproducing plants.

Genetics.   [back]  Plant geneticists use several techniques to assay the degree of relatedness among plants within and among populations. Mary Jo Godt of the University of Georgia analyzed Florida ziziphus populations using allozyme electrophoresis, a technique which identifies the genetic similarity among individuals using enzymes extracted from leaves. Her analysis revealed that the H01 site, based on BTG "captive" plants, is the most genetically diverse population with seven genotypes, while the other four populations each comprises a single genotype. A supplementary analysis by Tom Kubisiak of the USDA Forest Service, using a different technique (applied to only a subset of the material analyzed by Godt), has confirmed her results. Thus, Florida ziziphus may consist of as few as eleven genetically unique individuals (genets).

Populations consisting of a single genet are referred to as clones. Uniclonal populations of Florida ziziphus may have arisen through the fragmentation of a single vegetatively reproducing genet or through agamospermy, a process by which a plant produces viable seed without fertilization with the resulting offspring being genetically identical to the parent plant.

If four of the five extant populations of Florida ziziphus are sterile clones (or even closely-related incompatible genotypes), recovery of the species requires the introduction of compatible off-site genotypes to existing sites and the establishment of new populations comprising several compatible genotypes.

Breeding system experiments.    [back]  To gain an understanding of its reproductive biology and to assess the implications of the allozyme analysis, in 1995 we began a study of the breeding system of Florida ziziphus. Using flowering plants from all available genotypes, we performed hundreds of hand pollinations. Our results demonstrated that Florida ziziphus is an obligate outcrosser (plants of a given genotype are self-incompatible) and that populations consisting of a single genotype are thus incapable of sexual reproduction.

We found that most genotypes are also cross-incompatible. With the ten genotypes available, there were 45 possible crosses. Of the 31 test crosses performed so far, only 9 (29%) have yield fruit. Some crosses have not yet been done because of non-synchronous flowering or other logistical problems.

We found no evidence of agamospermy, and thus it seems that if four of the five extent populations consist of a single genet this condition arose through vegetative growth and fragmentation over a long period of time.

Ziziphus and fire.   [back]  For plants endemic to fire-maintained communities, adaptive management means the application of prescribed fire. The yellow sands preferred by Florida ziziphus and its occurrence on two sites with wiregrass and other sandhill species suggested that it is adapted to frequent (2-5 years), low intensity fire. Plants unburned for a decade or more seem to die back, although they sometimes resprout.

We first burned Florida ziziphus plants in January 1996 at the protected state forest site where two-thirds of the population had died since its discovery, leaving only about a dozen separate clumps of stems. We burned a few moribund plants which were completely covered with epiphytes. All burned plants resprouted within four months. Encouraged by these results, we burned most of the remaining plants in August 1996. Again all burned plants resprouted. But plants have shown little growth over the last two years and no plant has flowered.

Nonetheless, in the summer of 1998 we burned several moribund individuals at two other sites. At these sites, burned plants not only resprouted but have grown rapidly over the last eight months.

Translocation projects.   [back]  In a further effort to reverse the decline of the state forest population, in the summer of 1998 we carried out an experimental re-introduction of plants propagated at Bok Tower Gardens from root cuttings originally collected from the site. Our objectives were to assess the microhabitat requirements of Florida ziziphus, to augment the population by introducing healthier plants to the site, and to gain experience in translocating plants. While it is too soon to assess this translocation experiment, we are confident that it will teach us more about the ecology of the species.

Perspectives for future work.  [back]  Recovery of Florida ziziphus requires the establishment of several viable (sexually-reproducing) populations on protected sites.

At present, no site meets the viable population/protected site criterion. Our objective is the creation of such populations through research, translocation of genotypes, and aggressive management.

Although hundreds of hand pollinations yielded only an handful of fruit in our breeding system experiments, a substantial crop has been produced every year since 1994 from open-pollinated crosses involving the captive H01 genotypes at BTG (up to 2500 fruit). It is likely that these captive genotypes represent only a subset of the genetic variation present on the H01 site. We have only recently gained access to this site and have just begun to include it in our monitoring and research.

Moreover, we expect that BTG captive plants from the state forest site, which died back following flowering in 1995, will flower again in 2000. This will allow us to test the compatibility of this genotype with the other ten known genotypes for the first time. The last time the captive state forest plants flowered they did set fruit, with H01 captive genotypes as the putative pollen donors.

Meanwhile, we are planning an experimental introduction at a protected site based on cross-compatible genotypes. This translocation project represents the intersection of several recovery activities, including site acquisition, off-site propagation, and basic research. A recently acquired site will be used for the translocation of plants propagated at BTG, genetically defined by allozyme electrophoresis, and determined to be compatible by the breeding system studies.

Florida ziziphus is in the direst of conservation situations: small remnant populations, limited genetic diversity, restricted sexual reproduction, and few occurrences that are surrounded by intact ecosystems. The prospects are grim from a conservation perspective. But, we have to keep in mind that the history of this species is full of surprises, including its rediscovery, the existence of more genetic diversity that was thought to exist ten years ago, the documentation of five sites over the past twelve years, and its ability to produce viable seeds. With the contributions of researchers and with sympathetic landowners helping to preserve this species in the short term, we may learn enough over the next ten years to preserve Florida ziziphus for the long term.

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