Other Taxonomic Groupings: Subkingdom : Tracheobionta
Division : Magnoliophyta
Subclass : Arecidae
Species Description: Serenoa repens is the most common palm in the U.S. (Bennett and Hicklin 1998). It grows as a shrub that attains a height of 0.6 - 2.1 m (2 - 7 feet), or as a small tree that grows to 6 - 7.5 m (20 - 25 feet). Shrubs grow in a creeping horizontal form with many branches on their stems. As a tree, the crown projects above the many tangled branches. Stems run parallel to the soil, and can gradually bury to form rhizomes. Stems sprouted from rhizomes can measure 3 - 4.6 meters (10 to 15 feet) in length (Tanner et al. 1996). Two vegetative forms are recognized. The common type is yellow-green in color, while the less common type is a blue-green color sometimes referred to as the silver form (Essig et al. 2000). This type occurs in a continuous stretch in a narrow belt along Florida's east coast from St. John's to Dade Counties, and occasionally inland in Polk and Highlands Counties (Essig et al. 2000).
S. repens is easily recognized by its multiple leaves, or fronds, that protrude from horizontal stems the occur at or slightly below ground level. Fronds are evergreen and palmate (fan-shaped), measuring approximately 1 m (3 feet) in width. Petioles bear sharp spines from which this species earned its common name. Flowers are white and borne on stalked panicles growing from leaf axils. Fruit is a yellowish green in the unripe state, gradually turning blue-black as it ripens. Fruits are fleshy and ellipsoid in shape.
Regional Occurrence: Serenoa repens, saw palmetto, is endemic to coastal plains from South Carolina to southeastern Louisiana including the Florida peninsula.
IRL Distribution: Saw palmetto occurs in every county of Florida. It is common throughout the Indian River Lagoon area in both scrub and upland communities.
Age, Size, Lifespan: Maximum growth of established trees occurs during the summer rainy season, when up to 80% of annual production is accomplished from April through October (Olson and Barnes 1974). Estimates of stem growth range from 0.04 inches per year in Georgia to approximately 0.1 inch per year in Florida (Tanner et al. 1996). By using these estimates, Tanner et al. (1996) reported that some plants could be as old as 500 - 700 years.
Three to seven leaves are produced each year, and these may remain on the tree for as long as 2 years. Palmate leaves may measure 1 m (3 feet) in width (Tanner et al. 1996).
Serenoa repens attains a height of 0.6 - 2.1 m (2 - 7 feet) as a shrub, 6 - 7.5 m (20 - 25 feet) as a small tree. Its height is dependent upon the habitat it is grown in, with shrubs more common in scrublands, and trees more common in maritime hammocks and uplands.
Abundance: Saw palmetto is one of the more common shrubs in the scrub areas bordering the Indian River Lagoon. It is also highly abundant as an upland tree.
Reproduction: Saw palmetto grows vegetatively from horizontal stems and rhizomes. Sexual reproduction occurs via seeds. Flowers of Serenoa repens are pollinated by insects, and bloom from April through July (Hilmon 1969; Olson and Barnes 1974). Fruits ripen from September through October and are dispersed by animals (Olson and Barnes 1974).
Seedlings grow slowly, with plants becoming fully established after 3-6 years. Saturated soils that occur throughout the summer rainy season retard early growth. Flooding is a major preventative of establishment (Hilmon 1969).
Embryology: Germination may take as long as 6 months, as the fruit endocarp and seed coat must first deteriorate due to its impermeability to oxygen (Hilmon 1969). In laboratory studies, Hilmon (1969) found germination rates of approximately 55%; but field planting of seeds produced much lower rates of only 19.5%. It has been suggested that seed germination is enhanced by being passed through animal digestive tracts (Tanner et al 1996).
Temperature: Average annual temperature within the range of S. repens is from 4 to 36 °C (25 - 97 °F) (Wade and Langdon 1990).
Salinity: While this species is common on scrublands and in maritime forests, it may be somewhat sensitive to salt spray (Bennett and Hicklin 1998).
Physical Tolerances: S. repens is especially resistant to fire even though its foliage is highly flammable. It is a frequent invader to sites defoliated by previous fires (Abrahamson 1984b), and is classified as a survivor species due to its ability to resprout from rootcrowns and rhizomes following a fire. Leaf production following fire is initiated by using carbohydrates stored in rhizomes to increase stem density and production. Its fire response is so strong, that even if burned during the winter dormant season, S. repens will produce leaves and fruit out of season. S. repens recovers from fire very quickly, with cover returning to pre-burn levels within a year (Hilmon 1969; Abrahamson 1984a).
Trophic Mode: Autotrophic
Competitors: Serenoa repens seedlings are susceptible to competition from other scrub and upland plants (Hilmon 1969).
Habitats: S. repens is a characteristic component of pine flatwoods, prairies, scrub, and live oak-sea oats communities. It is a prominent indicator of in poorly drained soils in pine flatwoods (Tanner et al. 1996).
It generally grows best in dry, well-drained soils rather than in swampy areas (Monk 1965; Abrahamson 1984b). Typical soils are high in quartz and fine-grained, but this species is also known to grow on poorly drained sites high in peat (Breininger and Schmalzer 1990).
Saw palmetto grows best in warm-temperate, or humid-subtropical climates. Average rainfall within its range is approximately 100 - 163 cm (39 - 64 inches) per year, and average temperatures range from -4 to 36° C (25 - 97 °F) (Wade and Langdon 1990). This species grows well in either shade or in sun (Duncan and Duncan 1988), and is a common member of fire-climax communities (Wade et al. 1980; Taylor, and Herndon 1981).
It is a common understory shrub in coastal strands and in oak-pine communities. In scrub communities, saw palmetto provides habitat for sand skinks, the Florida mouse, and the threatened Florida scrub jay (Austin 1976). Its fruit provides food for black bear and white-tailed deer. In upland communities such as palmetto prairies, saw palmetto is primary habitat for burrowing owls, caracaras and sandhill cranes (Callahan et al. 1990).
Associated Species: Plants associated with saw palmetto commonly include overstory varieties such as slash pine (Pinus elliottii), pond pine (P. serotina), longleaf pine (P. palustris), sand pine (P. clausa) and cabbage palm (Sabal palmetto). Understory associates include live oak (Quercus virginiana), myrtle oak (Q. myrtlifolia), pawpaw (Asiminia reticulata), scrub mint (Conradina grandiflora) and gallberry (Ilex glabra) (Monk 1965; Austin 1976; Wade and Langdon 1990).
Florida wood rats, wild turkey and white-tailed deer are all known to use palmetto as cover or for nesting (Tanner et al. 1996). In addition to black bear and white-tailed deer, feral pigs, raccoons, foxes, deer, and gopher tortoises all utilize saw palmetto fruit for food. Black bear and feral pigs also eat apical meristems (hearts) of the plant (Bennett and Hicklin 1998).
Benefit in IRL: S. repens is an ecologically important species that provides nesting, protective cover and an important food source to other species of birds and mammals (Tanner et al. 1996).
At archaeological sites throughout central Florida, saw palmetto, sea grape (Cocoloba uvifera), and cocoplum (Chrysobalanus icaco) are all ubiquitous (Bennett and Hicklin 1998). Saw palmetto appears to have been one of the most important food sources for Florida's pre-Columbian population, for the later Miccosukee and Seminole tribes, and for subsequent settlers such as the Spanish during the sixteenth century. Even as late as the early 1900s, pioneers used saw palmetto berries to make soft drinks (Bennett and Hicklin 1998).
The medical value of S. repens has been reported since the 1800s (Hale 1898 in Tanner et al. 1996). Bennett and Hicklin (1998) reported over 50 medicinal uses of saw palmetto extracts for illnesses ranging from whooping cough to alcoholism.
Economic Importance: S. repens has previously been used to produce pulp for paper products, but it is considered to be of poorer quality compared with other tropical species (Olson and Barnes 1974).
Of significant importance is a drug called Serenoa, marketed as Permixon, which is extracted from partially ripened, dried fruits of saw palmetto. This drug has been successfully used to treat prostrate swelling, bladder infections and urinary tract infections. In prostate disorders, extracted Serenoa repens compounds inhibit the enzymes responsible for conversion of the male hormone testosterone to DHT, dihydrotestosterone, a hormone that binds to receptor sites on prostate cells, and adversely affects gene transcription and the regulation of biological responses in these cells (Plosker and Brogden 1996). In urinary tract disorders, treatment of men with S. repens compounds helped reduce urinary frequency, increase urinary flow, and improve symptoms of dysuria (painful urination).
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