Florida Ziziphus

Ziziphus celata

Description

Ziziphus celata (Florida ziziphus) is a spiny shrub that averages between 1.6-5 ft (0.5-1.5 m) in height, but can grow to over 6.5 ft (2 m). Plants occur in groups of stems, arising from what are assumed to be connected root systems. The primary branches are jointed and bent, and give rise to short, straight, spiny branchlets. The oblong-elliptic to obovate leaves are alternate and deciduous. The leaves are characterized by rounded tips, cuneate bases, and entire margins. The upper leaf surface is dark glossy green, while the underside is a dull light green. Leaves vary from 0.2-0.8 in (4.5-21 mm) in length, and from 0.1-0.5 in (3-13 mm) in width. Fragrant Florida ziziphus flowers are small, axillary, and solitary, but are tightly bundled on short shoots. Flowers have five greenish-yellow sepals, and five white petals clasping five stamens, however, three and four-merous flowers have been observed. The bright yellow drupes range from 0.4-0.8 in (10-20 mm) long, and 0.1-0.4 in (3-10 mm) wide.

Florida ziziphus is deciduous, losing its leaves in late fall. It begins blooming in late December or early January and blooming continues through late February, while the branches are still bare. Fruits begin to develop in March, with new leaves forming at the same time or soon after. The fruits ripen in May or early June. No seedlings have been found in the wild, so it is not known whether the seeds germinate in the summer or later in the year. Common pollinators have been observed visiting the flowers, although it is not known if these are pollinators of Ziziphus. No viable seeds have been observed in the wild. Natural fruit set has been observed twice in the wild, but few fruit were produced, and all of those aborted before maturity. Lack of sexual reproduction may be due to the absence of compatible genotypes at a given site and/or the age of the aboveground stems.

Florida ziziphus spreads asexually by sending shoots up from its roots. These additional stems give Florida ziziphus a clump-like appearance, where individual plants in the clump are not distinguishable. Like other members of its genus, Florida ziziphus is capable of parthenocarpic production of fruit, but it differed from others in its genus in not being dichogamous, having pistils and stamens that mature at different times to prevent self-fertilization.

Habitat

Florida ziziphus appears to prefer high pine habitat or the transition zone between scrubby flat-woods and high pine. The healthiest plants grow on the lower slopes of turkey oak knolls with sparse cover. Based on Soil Conservation Service mapping, all of the sites where Florida ziziphus occurs are characterized by excessively drained, nutrient poor soil types, including Tavares Fine Sand, Astatula, and Candler Sand.

Three of the five sites where Florida ziziphus occurs are improved pasture. The Lake Wales Ridge State Forest (SF) site is a degraded narrow ecotone between a high pine ridge and scrubby flatwoods. Other species in this ecotone include Quercus sp., Bumelia tenax, Sabal etonia, Erigonium tomentosum, E. longifolium, and Serenoa repens. The fifth site referred to as the sandhill site, lies along the sloping edge of former sandhill. The site is surrounded by cherry laurel, oaks, and invading blackberry. Within the site, Florida ziziphus is associated with longleaf pine, wire grass, scrub buckwheat, and Serenoa repens. Habitat characterization for this species is difficult since many of the known sites are in pasture, with one site identified as a remnant sandhill and another an open oak-hickory, yellow sand scrub. This species seems to prefer un-shaded and uncrowded microsites within these communities.

Distribution

The original Florida ziziphus herbarium specimen was collected from a scrub site near Sebring, Highlands County, Florida. Despite extensive searches, no specimens have been located in this area since 1955. Florida ziziphus occurs at five known sites; four sites in Polk County and one in Highlands County, all on the Lake Wales Ridge of central Florida. Based on historic and existing locations, the north to south range of this species was approximately 35 mi (56 km), and included much of the Lake Wales Ridge, from Highlands County north to at least central Polk County, and possibly further north.

Threats

The main threats to Florida ziziphus are habitat loss, potential reproductive and genetic limitations, exotic species invasion, and the potential for over-collection and vandalism. Most Florida ziziphus habitat was converted to pasture and citrus production before the species was rediscovered in 1987. Lack of protection on private land and reproductive failures in the wild make this species more vulnerable to extinction.

Land conversion for agriculture and residential housing on the Lake Wales Ridge has greatly reduced the amount of Florida ziziphus habitat and has caused much of the remaining habitat to become even more isolated. If cross-pollination is necessary between sites, increased isolation will decrease the chance of successful seed production. The further loss of any genetic material will weaken the possibilities of recovery for this species.

Fruits of southwestern Ziziphus species are eaten by birds. Herbivory on stems and leaves has been observed in the wild. Rabbits have been observed eating the pulp from fruits which had fallen to the ground, and other animals such as rodents and gopher tortoises may also find the fruits palatable. The dense thorny branches provide protection for small animals; rabbits, lizards, and nesting mockingbirds have been observed using these plants as cover at Bok Tower Gardens.

Conservation and Recovery

Florida ziziphus plants at Lake Wales Ridge SF were heavily shaded, covered in lichens, and appeared stressed, yet regenerated quickly after prescribed fire. Plants at the more open high pine site and open pasture sites appear to grow vigorously in full sun or light canopy. This combination of a need for open canopy and quick regeneration suggests that this species is adapted to the frequent fire regime which historically maintained the high pine ecosystem.

The Lake Wales Ridge SF is the only site on public lands where Florida ziziphus is protected. Current management activities at this site include semi-annual monitoring and prescribed burning. An augmentation project is proposed for this site.

The Highlands County population occurs in improved pasture on private property. Access to this site has been restricted and these plants have not been included in the regular monitoring program. This population was sampled in 1989 and propagated for the National Rare and Endangered Plant Collection at Bok Tower Gardens. Management needs for this population include: developing contact with the landowners, including this group in the regular monitoring program, and propagating additional samples to ensure that a backup of all genetic variability is preserved.

The two populations of Florida ziziphus that occur in improved pasture on private lands in Polk County have similar management needs. Both sites are open and the plants are fairly vigorous, flowering annually. However, plants at one site are impacted by livestock and many of the older stems are dying due to old age and trampling. The landowner has fenced this site for protection. Plants at both sites are included in the regular monitoring program. Since the site has been fenced, fire management is now being implemented. Fire management burns some of the older stems and encourages new growth.

The population on the remnant sandhill site on private property in Polk County is currently protected. The owners have posted the property as a nature preserve. However, the main threat to this population is invasive exotics. Bok Tower Gardens and the Department of Agriculture and Consumer Services Division of Forestry have implemented some control of these species, but this control will need to be continued. Prescribed fire is recommended for portions of the site, in order to limit the spread of exotics, encourage the growth of natural ground-cover, and stimulate vigorous new growth of Florida ziziphus. In addition, this population should be sampled and propagated for inclusion in the Bok Tower Gardens collection of endangered plants.

Management for Florida ziziphus on private land depends on competing land uses and on the landowners' willingness to embrace land management techniques that will benefit this species. Unfortunately, none of the sites on private land is secure at this time. On the three pasture sites Florida ziziphus has been exposed to mowing. Though currently not a problem, Florida ziziphus only produces flowers on woody vegetation, so if mowing were done more frequently than every two to three years, the plant would be unable to reproduce. Other threats such as trampling and competition with invasive and exotic vegetation can only be eliminated if the private landowners support management recommendations.

To offset possible losses from private lands, plants have been propagated from three different sites and are maintained in the Center for Plant Conservation National Collection at Bok Tower Gardens. Plants representing two sites produced seed in 1994; plants from one site produced seed in 1995. Because the species is easily propagated, it appears feasible to establish new populations at the Lake Wales Ridge SF and other suitable sites.

Contacts

U.S. Fish and Wildlife Service
Ecological Services Field Office
6620 Southpoint Drive South, Suite 310
Jacksonville, Florida 32216-0958
Telephone: (904) 232-2580
Fax: (904) 232-2404

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

Burkhart, S., T. Race, and C. Weekley. 1997. "Breeding System of the Rare Florida Endemic, Ziziphus celata." Report to U. S. Fish and Wildlife Service; Vero Beach, Florida.

Judd, W. S., and D. W. Hall. 1984. "A New Species of Ziziphus (Rhamnaceae) from Florida." Rhodora 86:381-387.

Peroni, P. A., and W. G. Abrahamson. 1985. "A Rapid Method for Determining Losses of Native Vegetation." Natural Areas Journal 5:20-24.

U.S. Fish and Wildlife Service. 1990. "Scrub Blazing Star (Liatris ohlingerae ) and Florida Ziziphus (Ziziphus celata )." http://endangered.fws.gov/i/q/saq5n-.html.

U.S. Fish and Wildlife Service. 1995. "(Draft) Recovery Plan for Nineteen Florida Scrub and High Pineland Plants." U.S. Fish and Wildlife Service, Atlanta.

Wallace, S. R. 1990. " Ziziphus celata : Uphill Climb for a Rare Florida Endemic." Botanic Gardens Conservation News. 1 (7): 45-47.

Wunderlin, R. P., et al. "Status Report on Ziziphus celata." Report. Department of Biology, University of South Florida, Tampa.