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Saw-palmetto: an Ecologically and Economically Important Native Palm 1
George W. Tanner, J. Jeffrey Mullahey and David Maehr2Overview
Saw-palmetto (Serenoa repens) , also known as palmetto, is endemic to the southeastern United States, occurring as a major understory plant on poorly drained pine flatwoods, on well-drained scrubby flatwoods, and in sand pine (Pinus clausa) scrub. It currently occurs in every county in Florida. Its distribution becomes spotty in the northern part of its range which extends from Charleston County, SC, to southern Mississippi (Hilmon 1968). This low-growing palm is recognized by the multiple, persistent leaves, or fronds, protruding from the terminal end of long, horizontal stems that occur at, or just below, ground level. Sharp, spine-like projections often exist along the edges of the compressed leaf petiole and give rise to the plant's common name. This petiole terminates at the edge of the leaf blade, but does not protrude into the leaf blade structure.Plant Description
Saw-palmetto stems may be partially or completely underground and can reach 10 to 15ft in total length. Typically, the stems lie prostrate at the soil surface, but occasionally they grow upright and reach heights of 15 to 20ft. Some stems begin to deteriorate at one end as new material is produced at the apical meristem (bud) at the other end. Stem growth has been estimated to range from 0.04in/yr in southern Georgia to about 0.1 in/yr in central Florida. Using these estimates, some saw-palmetto plants may be 500 to 700 years old. Roots are located on the ventral side of the stem and are concentrated near the growing end. Most roots are located within the upper 12 inches of the soil column, however, roots may extend several feet into well-drained sandy soils.Approximately 3 to 7 leaves are produced every year and remain alive on the plant for about 2 years. Mature leaves are palmate shaped and range in size from 1.5 to 3ft wide. The sinuses between veins are split towards the outer edge of the leaf. Leaf color is green throughout most of its range except along Florida's east coast where leaves can be a light, bluish green. Dead leaves remain on the plant for a year or more, are extremely flammable, and make fuel that increase this plant's ability to carry a fire. After burning, new leaf tissue emerges within a week.
During spring, saw-palmetto plants produce one to three prominent clusters (spadix) of many white flowers, and fruit matures during summer. However, individual plants may flower throughout the year, but their fruit seldom matures outside of the normal summer fruiting period. These flowers are insect-pollinated and are used extensively by honey bees. The fruit is a single-seeded drupe that is surrounded by a fleshy pulp. As ripening occurs, fruits turn in color from green (May-June) to yellow (mid-August), to orange (September), and then to bluish-black (September-October) when ripe. Fruit production can be variable over the years. Annual number of seeds/plant has been measured to vary between 100 and 500 in mid- to late-June, but decrease rapidly until mid-October when no fruits remained on the plants (Hilmon 1968).
Seed germination in the lab averages about 55% (Hilmon 1968). Germination began 45 days after planting, but optimal rates of germination began 4.5 to 6 months after planting. Germination of seeds planted near Arcadia, FL, averaged just 19.5% after 15 months. Shoots emerged from the soil 30 to 60 days after seed germination. Seed germination may be enhanced after passing through animal digestive systems. Longevity of seed viability is not known.
Associated Plants
On the dry prairie grasslands and cut-over pine flatwoods of south Florida, saw-palmetto often is the dominant woody plant. This species also may occur as a co-dominant with several oak species on scrubby flatwoods sites. It is theorized that infrequent burning and/or burning outside the growing season has allowed this species to become more dense throughout much of its range than was described by early European explorers. Also, extensive drainage projects throughout south Florida may have promoted saw-palmetto expansion. Other woody plants that commonly occur with saw-palmetto are gallberry (Ilex glabra) , wax myrtle (Myrica cerifera) , staggerbush (Lyonia ferruginea) , and runner oaks (Quercus spp.) . Commonly associated herbaceous plants include wiregrass (Aristida beyrichiana) , several bluestem species (Andropogon spp.) , lop-sided indiangrass (Sorghastrum secundum) , and numerous forbs.From south Florida to the northern extent of saw-palmettos range, this plant can become the major woody species in the understory beneath canopies of slash pine (Pinus elliottii) and longleaf pine (P. palustris) . Regardless of the region, plant associates of saw-palmetto are adapted to frequent growing-season fires, and can withstand periodic drought and flooded conditions.
Ecological Importance
Many species of wildlife use saw-palmetto for nesting, protective cover, and as a food source. The endangered Florida grasshopper sparrow (Ammodramus savannarum) places its nests in association with palmetto, and the Florida panther prefers this plant for both day rest sites and natal dens. The labyrinth of stems often is used for structural support for ground-nesting rodents such as the Florida woodrat (Neotoma floridana) . Wild turkey (Meleagris gallopavo) is known to use palmetto as nesting cover, and white-tailed deer (Odocoileus virginiana) will use it as escape cover when pursued, or as bedding cover on the leeward side of clumps during windy, cold winter days.Various parts of the plant are eaten by a wide variety of animals. The apical meristem material (or heart) is physically extracted and consumed by black bears (Ursus americanus) and feral pigs (Sus scrofa) . They accomplish this by grasping the newest leaves in their mouth, pulling the leaves out, and consuming the bases. Feral pigs readily forage in this manner on fresh regrowth following a fire. Such herbivory will often cause adventitious sprouting and branching of individual plants. Cattle will forage on the fronds during the winter, especially when fed supplements containing urea-based nitrogen compounds, such as molasses. Although palatability of the fronds is low (<30% digestible), phosphorous content is relatively high for a native flatwoods species. Many species of insects forage on the fleshy pulp of the fruit while it's on the plant or after it falls onto the ground.
Several species of wildlife seek out the fruit as excellent sources of oils and carbohydrates. Black bears have been documented to forsake established home ranges in favor of areas containing large stands of saw-palmetto during late summer when their fruit is ripe. At times, bears also have been known to engorge themselves on the fruit. A road-killed adult female bear in the Ocala National Forest was found to have over 30 lbs. of palmetto fruit in her stomach. White-tailed deer and other mid-sized mammals, including the raccoon (Procyon lotor) , opossum (Dasypus novemcinctus) , and gray fox (Urocyon argenteus) readily consume the fruit. All of these species serve as seed dispersal agents as the seeds pass through their digestive systems and are distributed in feces throughout the landscape.
Management and Use
As Europeans occupied Florida and the southeastern region of the U.S., saw-palmetto presented itself as an obstacle to establishing crop fields, pastures, and homesites. The plant is adapted to fire, so simply burning areas did not remove it: The plant had to be physically eradicated from the areas being converted to other uses. Various pieces of mechanical equipment were developed to assist in this process. The web plow and heavy duty discs were used to kill the plant (Tanner et al. 1985), but the remains of the stems had to be raked into piles and burned. Ranchers wanting to reduce the competition with native forage grasses, or foresters preparing a site to re-plant pine trees, used roller-drum choppers, pulled behind rubber-tired tractors or caterpillars, to crush the palmetto to temporarily (4 to 6 years) reduce the foliar cover of the plant.Further, use of native plant species for landscaping recently has increased in popularity with saw-palmetto as one of the plants people want to use. However, landscapers have found it difficult to transplant this species from the wild and have it survive. Consequently, nurseries specializing in native species have began to raise plants from seed to supply market demand. Saw-palmetto is naturally drought- and insect-resistant, requires no fertilizer, and is a perfect plant for enviroscaping.
The fruit of saw-palmetto has been eaten by humans for centuries. Hale (1898) speculated that palmetto fruit was a staple food item for the aborigines in Florida, although the taste is reported to be repugnant. The medicinal value of the fruit has been described in scientific literature since the 1800s. Hale (1898) described tinctures of the fruits and crushed seeds being used for relief of prostate gland swelling and various aphrodisiac qualities. Permixon, a pharmaceutical extract of saw-palmetto fruit, possesses antiangrogenic activity that significantly improves symptoms of human benign prostatic hypertrophy (Sultan et al. 1984, Di Silverio et al. 1992). Commercialization of the fruit has been active for several decades at least. Hilmon (1968) described an advertiser in southern Georgia wanting to purchase 40,000 to 50,000lb of dried fruit in 1961 for $0.12/lb. The fruits were being processed and resold to wholesale drug manufactures.
In 1995, the economic value of saw-palmetto fruit made the news when the price for raw fruit exceeded $3/lb. Thus, a plant that had been viewed as a pest promises to add economic value to the landscape. The current demand for the fruit by pharmaceutical companies is projected to remain strong. Saw-palmetto-based products are also sold in health food stores. Today, just as it was a century ago, the fruit is processed for treatment of prostate gland swelling.
Managing Fruit Production
To date, a single study has been conducted that quantitatively described fruit production in relation to fire, the primary disturbance agent in saw-palmetto country. Hilmon (1968) tagged 20 plants that had not been burned in four years and followed flowering and fruit production for the next six years. The number of fruit per plant was approximately 400 in 1961, 1963, and 1964. In 1960 and 1965, only 100 fruit per plant were produced, and no fruit were produced in 1962 even though 45% of the marked plants flowered. Fruit production was scattered during the first four years following fire. This response has been hypothesized to be related to reduced carbohydrate levels in plants following fire--as it was found to take approximately four years following a winter fire (time of maximum stored carbohydrate level) for carbohydrates to reach pre-burn levels in the stems. Plants burned on alternate years seldom produced fruit, although flowering occurred in the spring following the burns. Mr. Ralph Hughes, range scientist for the Southeastern Forest Experiment Station, Tifton, GA, indicated to J.B. Hilmon that palmettos in south Georgia did not consistently set seed unless protected from fire for 5 to 10 years.Past scientific work and casual observations of plant ecologists indicate that fruit production in saw-palmetto is tied to time since the last burn. At least four years without fire may be required before the plant is physiologically able to expend the energy to produce fruit. Landowners who regularly burn their flatwoods and palmetto prairie pastures to stimulate grass production for livestock forage may need to lengthen the burning interval if they plan saw-palmetto fruit production.
Cautionary Note: Landowners wanting to manage for game and/or nongame wildlife populations on their property may not want to harvest all the saw-palmetto fruit produced each year. Most omnivorous species of wildlife seek out the fruit whenever it is available. It is presently unknown what effect total removal of these fruit year after year may have on the resident wildlife populations that inhabit the property.
Literature Cited
Di Silverio, F., G. d'Eramo, C. Lubrano, G.P. Flammia, A. Sciarra, F. Plama, M. Caponera, and F. Sciarra. 1992. Evidence that Serenoa repens extract displays an antiestrogenic activity in prostatic tissue of benign prostatic hypertrophy patients. Eur. Urol. 21:309-314.Hilmon, J.B. 1968. Autecology of saw palmetto ( Serenoa repens [Bartr.] Small). Ph.D. Diss., Duke Univ., Durham, NC. 191 pp.
Sultan, C., A. Terraza, C. Devillier, E. Carilla, M. Briley, C. Loire, and B. Descomps. 1984. Inhibition of androgen metabolism and binding by a liposterolic extract of "serenoa repens B" in human foreskin fibroblasts. J. Steroid Biochem. 20:515-519.
Footnotes
1. This document is WEC109, one of a series of the Wildlife Ecology and Conservation Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date July, 1996 as Circular WEC-109. Reviewed September, 2002. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.2. George W. Tanner, professor, Wildlife Ecology and Conservation department, J. Jeffrey Mullahey, associate professor, Southwest Florida REC, Immokalee, and David Maehr, graduate research assistant, Wildlife Ecology and Conservation department, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611.
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U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.
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