Seedlings grown from seeds placed into an introduction Photo Credit: Archbold Biological Station’s Plant Ecology Program

Author: Rohan Patel

We are situated on a unique landscape, the Lake Wales Ridge. Formed millions of years ago when most of Florida was underwater, it is one of the most diverse spots in Florida, home to dozens of rare and endangered species found nowhere else on Earth. One of the rarest is Florida Ziziphus..

Florida Ziziphus, or Ziziphus celata, is a shrub in the buckthorn family with thin, spiny stems and small, round leaves. Although the leaves are shed during the winter and early spring, fragrant flowers adorn the plant in January and fruits ripen in spring. Florida Ziziphus spreads by underground runners, forming large clones in some places.

Despite its ordinary appearance, it has an immensely rich history. Interestingly, the closest living relative to the species, Ziziphus parryi, is found in southern California and adjacent Mexico. This extremely large gap between the Florida Ziziphus and its relative could be explained by the following theory: millions of years ago, when sea levels were much lower, a land mass existed that connected Florida and California. The ancestor of Florida Ziziphus was able to spread over the land mass and occupied a region from Florida to Southern California. As sea levels rose, the land mass disappeared, and two related species now exist on opposite sides of the continent. This shows the ancient heritage of Florida Ziziphus, which dates back millions of years.

Florida Ziziphus is an extremely endangered plant of Florida. Hanna Rosner-Katz, a biologist at the Florida Forest Service explains, “The story of Florida Ziziphus demonstrates the importance of persistence by local biologists when it comes to plant conservation.” It was first discovered in Sebring, 1948, by Ray Garrett. However, it was presumed extinct even before being named Ziziphus celata. It remained out of sight from botanists for almost 30 years until in 1987, it was rediscovered by Avon Park botanist Kris DeLaney. Carl Weekley, retired plant ecologist who worked at Archbold for many years, was one of the first biologists to intensively study the species. He says, “When Archbold began working with Florida Ziziphus in 1995, only one of the four known populations was on publicly protected land, and collectively they comprised only six unique genotypes (genetic individuals).” Since then, 16 known populations of Florida Ziziphus have been found in Florida, all on the Lake Wales Ridge in Highlands and southern Polk Counties. However, 10 of those populations are uniclonal, meaning the population is simply clones of a single genetic individual. This makes these populations very vulnerable to any changes in the environment. The good news is that a few of the other populations are more diverse and hold multiple genetic individuals.”

According to Michael Jenkins, a Plant Conservation Program biologist at the Florida Forest Service, “Many different challenges face those trying to propagate the plant: physiological, genetic, environmental, and a very slow growth rate”. Because of the significant concern for the future of the species, the Plant Ecology Program headed by Dr. Eric Menges at Archbold Biological Station is closely involved in research on this species’ problems and potential solutions. “This is one of our most varied and intense research and conservation projects”, explains Menges. In collaboration with the Missouri Botanical Garden, Archbold scientists found that there are only ~40 different Florida Ziziphus genetic individuals in the world. Because most wild populations have no genetic variation, they do not produce fruits. Due to this lack of reproduction and its limited range, the Florida Ziziphus is considered extremely endangered.

High school research assistants Lukas High and Amy Platt prepare to outplant Florida Ziziphus Photo Credit: Stacy Smith

Menges’ Program has been conducting long-term research for the past two decades to evaluate the best way to reintroduce Florida Ziziphus plants back into viable habitats along the Lake Wales Ridge. They have found that transplanting is the most successful way to introduce plants into new habitats. Transplants were more resilient and survived better in response to fire compared to plants grown from seeds. The introductions can include many genetic individuals, which may allow these new populations to produce fruits. Recently, and for the first time, an introduced population not only produced fruit, but germinated a new, second generation seedling! Archbold research assistant Stephanie Koontz explains “The new seedling generation is an important milestone in the recovery of Florida Ziziphus”. Currently they are focusing on developing improved methods to successfully introduce plants into multiple new sites, in order to restore this species back to its diverse, healthy self. “An interesting research finding at Bok Tower Gardens is that seed germination of Florida Ziziphus appears to be enhanced by digestion of the fruit by Gopher Tortoises. This could bode well for the new populations that have been introduced in the wild.  From our greenhouse studies, Florida Ziziphus has a notoriously low seed germination rate, but the presence of Gopher Tortoises in the wild populations might help promote germination success” says Cheryl Peterson, Conservation Manager at Bok Tower Gardens in Lake Wales, Florida.

Fruits of Florida Ziziphus Photo Credit: Stephanie Koontz

Peterson notes, “Florida Ziziphus is a unique plant species that could easily have gone extinct without a great amount of effort to understand and preserve it. The successful conservation of the Florida Ziziphus is a good example of how different conservation research institutions and agencies can work together across a wide range of research topics and help a species that was on the brink of extinction to recover.” As Weekley puts it, “We’ve made significant progress in understanding the biology and ecological needs of this difficult species. However, much work remains to be done to ensure the long-term viability of this thorny poster child for the challenges of restoring endangered species.”