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Species Name:    Uniola paniculata
Common Name:     

               (Sea oats)

 

I.  TAXONOMY

Kingdom Phylum/Division: Class: Order: Family: Genus:
Plantae Tracheophyta Liliopsida Cyperales Poaceae Uniola

Sea oats, Uniola paniculata growing on the upper beach.  Photo Courtesy of J. Bauer, Smithsonian Marine Station volunteer.


Close-up of seed heads of Uniola paniculata.  Photo Courtesy of J. Bauer, Smithsonian Marine Station volunteer.


Species Name:

Uniola paniculata (L.)

Common Name:
Sea oats, seaoats

Synonymy:
None

Other Taxonomic Groupings:
Subkingdom : Tracheobionta
Division : Magnoliophyta
Subclass : Commelinidae

Potentially Misidentified Species:
None

Description:
Uniola paniculata is a semitropical perennial that dominates beach and dune communities (Sylvia 1986; Hester and Mendelssohn 1989, 1991; Bachman and Whitwell 1995). It is a tall, erect grass whose leaves grow 20-40 cm (8-16 inches) in length, and approximately 0.6 cm (1/4 inch) in width. Leaves are thin and taper into pointed tips. 


Seed heads are large, and become a yellow-brown, straw color in late summer (amos and Amos 1997). Its growth functions to trap wind-blown sands that eventually mound to begin dune formation (Johnson and Barbour 1990). This species is both an excellent pioneering species due to its ability to rapidly colonize and establish itself, and an excellent climax species due to its high tolerance to sea water and salt spray. U. paniculata forms dense surface roots and penetrating deep roots (Hester and Mendelssohn 1987). Rhizomes are elongate and extensively creeping in habit.  They readily root upon burial in sand (Hitchcock 1951; Clewell 1985; Duncan and Duncan 1987). Rhizomes produce extensive lateral growth which stabilizes continuous dune ridges (Duncan and Duncan 1987).

Plants grow 1-2 meters tall (6 feet) with individual leaf blades reaching approximately 60 cm (24 inches). Flowering spikelets are flat and measure 20-50 cm (10-20 inches) (Radford et al. 1968). 


II.  HABITAT AND DISTRIBUTION

Regional Occurrence:
U. paniculata occurs from Northhampton County, Virginia through Florida, the Gulf Coast, and Texas, south to Tabasco, Mexico. Sea oats is also widely distributed throughout the Bahamas and some areas of northwestern Cuba.

IRL Distribution:
Uniola paniculata occurs throughout the extensive barrier island system bordering the Indian River Lagoon. It is the dominant plant species on foredunes and dune crests.


III.  LIFE HISTORY AND POPULATION BIOLOGY

Age, Size, Lifespan:
Growth in this species can be rapid under optimal conditions and is stimulated by burial in sand. Plants grow as tall as 1-2 meters (approximately 6 feet), with leaves measuring up to 60 cm (24 inches), and spikelets of 20-50 cm (10-20 inches) (Radford et al. 1968).

Abundance:
Sea oats is perhaps the most abundant plant of beach dune communities (Sylvia 1986; Hester and Mendelssohn 1989, 1991; Bachman and Whitwell 1995).

Locomotion:
Sessile.

Reproduction:
Uniola paniculata primarily reproduces vegetatively by forming buds around stem bases, but also reproduces sexually via seeds. U. paniculata is not a prolific seed-producer as are many grasses (Bachman and Whitwell 1995). Production of large numbers of seeds probably requires cross pollination (Hester and Mendelssohn 1987). Generally, many spikelets bearing 10-12 florets are produced. However, florets are usually infertile at both the terminal and distal ends (Bachman and Whitwell 1995), leaving only 6 8 florets to produce seeds. Seed production tends to be lower in low latitudes. In one study, plants in North Carolina, produced an average of 2.24 seeds per spikelet, while those in Florida produced only 0.6 seeds per spikelet (Hester and Mendelssohn 1987). High incidence of fungal invasion of aborted ovules has been observed (Bachman and Whitwell 1995).

Pollination is accomplished by winds. Florets open and close during the early morning, and open only once. Seeds in spikelets are rapidly dispersed by winds and quickly bury in accreting sands. Seeds may be carried long distances by winds, storms and ocean currents (Oosting 1954).

The growing season of U. paniculata varies by geographic location. In North Carolina, growth occurs from May to September, with seeds germinating from late May through mid-June (Tyndall et al. 1987). In Florida, Uniola paniculata flowers and sets fruit from spring through fall (Wunderlin 1982), while in Texas, flowering and fruiting occurs from April through November (Gould 1978).


IV.  PHYSICAL TOLERANCES

Temperature:
Like other grasses, northern populations of U. paniculata have a cold requirement in order to break dormancy. However, Florida populations have no such requirement.

U. paniculata suffers little to no adverse effects under high temperature conditions, where, during summer, temperatures in the top inch of sand may reach as high as 52 - 53 C (125-127 F) when air temperature is approximately 35-38 C (95 100 F) (Oosting 1954).

Salinity:
U. paniculata is highly tolerant of innundation by sea water for short periods, and thrives under salt spray conditions. It is thought that salt spray may provide a source of micronutrients for sea oats, which normally grows in the heavily leeched soils of beach sands (Hester and Mendelssohn 1990; Stalter and Odum 1993).

Physical Tolerances:
Uniola paniculata is tolerant of a wide variety of harsh environmental conditions including drought, inundation by sea water, salt spray, strong winds, storm effects, and periodic fires.

Stoma close when soil moisture reaches 8.5%. This differs from many plants whose stoma do not close until soil moisture reaches 1.2% (Hester and Mendelssohn 1987). While highly tolerant of drought conditions, sea oats does not tolerate waterlogging of roots; which can kill sea oats after only a few days (Hester and Mendelssohn 1987; 1989).

Soil pH in Jupiter, Florida was measured at 7.5. In other areas of its range, soil pH for Uniola species ranges from 6.9 7.9 (Oosting 1954).

U. paniculata is adversely affected by encroachment by urban development. Sewage, both treated and untreated, urban runoff and pollution from marinas all impact growth in this species. Further, off-road vehicles damage sea oats growth by compacting beach soils and damaging roots (Stalter and Odum 1993).


V.  COMMUNITY ECOLOGY

Trophic Mode:
Autotrophic.

Competitors:
May compete with other salt-tolerant coastal species; however, U. paniculata is the dominant species on foredunes and dune crests.

Habitats:
There is a close association between the occurrence of U. paniculata, and the salt spray zone along coastal beaches. It is primarily found on foredunes and dune crests along the eastern Atlantic coast from Virginia though Florida, but is not common in the swales between dune crests where salt spray effects are lessened (Johnson and Barbour 1990; Stalter and Odum 1993). This species is seldom found inland of the shore zone.

Associated Species:
U. paniculata seeds provide food for many coastal strand species such as the red-winged blackbird, which is the primary consumer of sea oats seeds. Other species include songbirds, especially sparrows; marsh rabbits, and mice (Johnson et al. 1974; Johnson and Barbour 1990).

Other plants associated with sea oats in the beach dune community include beach purslane, also called sea pickle (Sesuvium portulacastrum), railroad vine (Ipomoea pes-capre), beach morning glory (Ipomoea stolonifera), beach sunflower (Helianthus debilis), beach dropseed (Sporobolus virginicus), beach berry (Scaevola plumieri), seashore elder (Iva imbricata), and bay cedar (Suriana maritima).

Roots of sea oats also become colonized with beneficial microorganisms such as vesicular-arbuscular mycorrhizal (VAM) fungi. These organisms increase the surface area for nutrient absorbtion to plant roots, thus improving nutrition in sea oats communities. The hyphae of these fungi may also help in binding sand grains into aggregates, and aid in stabilizing substrata (Sylvia 1986).


VI.  SPECIAL STATUS

Special Status:
Habitat structure

Benefit in IRL:
Beyond its aesthetic value along coastlines, U. paniculata is a stabilizer of dune systems due to its extensive system of rhizomes which produce lateral growth. It is extensively used from Virginia through Florida to build artificial dunes and to stabilize existing dunes that have been damaged by storms (Bachman and Whitwell 1995).

Economic Importance:
U. paniculata has indirect economic importance to coastlines due to its ability to build and stabilize dunes along shorelines, thus protecting property from storm damage due to high winds, storm surges, and tides.


VII.  REFERENCES

Amos, W.H. and S.H. Amos. 1997. National Audubon Society Field Guides:
      Atlantic and Gulf Coasts. Alfred A. Knopf, Inc. New York, NY. p. 550.

Bachman, G.R. and T. Whitwell. 1995. Nursery production of Uniola paniculata
    
(southern sea oats). HortTechnology 5(4):296-298.

Clewell, A. F. 1985. Guide to the vascular plants of the Florida Panhandle. Florida
      State University Press. Tallahassee, FL. 605 pp.

Duncan, W.H. and M.B. Duncan. 1987. The Smithsonian Guide to seaside plants
      of the Gulf and Atlantic Coasts from Louisiana to Massachusetts, exclusive of
      lower peninsular Florida. Smithsonian Institution Press. Washington, D.C. 
      409 pp.

Gould, F.W. 1978. Common Texas grasses. Texas A & M University Press.
      College Station, Tx. 267 pp.

Hester, M. W. and I. A. Mendelssohn. 1987. Seed production and germination
      response of four Louisiana populations of Uniola paniculata (Graminae).
      American Journal of Botany. 74(7):1093-1101.

Hester, M. W. and I. A. Mendelssohn. 1989. Water relations and growth
      responses of Uniola paniculata (sea oats) to soil moisture and water-table
      depth. Oecologia. 78(3):289-296.

Hester, M. W. and I. A. Mendelssohn. 1990. Effects of macronutrient and
      micronutrient additions on photosynthesis, growth parameters, and leaf nutrient
      concentrations of Uniola paniculata and Panicum amarum. Botanical
      Gazette. 151(1):21-29.

Hester, M. W. and I. A. Mendelssohn. 1991. Expansion patterns and soil
      physiochemical characterization of three Louisiana populations of Uniola
      paniculata
(sea oats). Journal of Coastal Research 7(2):387-401.

Hitchcock, A.S. 1951. Manual of the grasses of the United States. Misc. Publ.
      No. 200, U.S. Department of Agriculture, Agricultural Research
      Administration. Washington, D.C. 1051 pp.

Johnson, A. F. and M. G. Barbour. 1990. Dunes and maritime forests. In: Myers,
      R.L. and J.J. Ewel, eds. Ecosystems of Florida. University of Central Florida
      Press. Orlando, FL. pp. 430-480

Johnson, A.S., O. Hilburn, S.F. Shanholtzer, and G.F. Shanholtzer. 1974. An
      ecological survey of the coastal region of Georgia. Scientific Monograph Series
      No. 3, NPS 116. U.S. Department of the Interior, National Park Service.
      Washington D.C. 233 pp.

Oosting, H.A. 1954. Ecological processes and vegetation of the maritime strand in
      the southeastern United States. Botanical Review. 20: 226-262.

Radford, A.E., H.E. Ahles, C.R. Bell. 1968. Manual of the vascular flora of the
      Carolinas. The University of North Carolina Press. Chapel Hill, NC. 1183 pp.

Stalter, R., and W. Odum. 1993. Maritime communities. In: Martin, W.H., S.G.
      Boyce, and A.C. Echternacht, eds. Biodiversity of the southeastern United
      States: Lowland terrestrial communities. John Wiley and Sons, Inc. New
      York, NY. pp. 117-163.

Sylvia, D.M. 1986. Spatial and temporal distribution of vesicular-arbuscular
      mycorrhizal fungi associated with Uniola paniculata in Florida foredunes.
      Mycologia 78(5):728-734.

Tyndall, R.W., A.H. Termura, C.L. Mulchi, and L.W. Douglas. 1987. Effects of
      salt spray upon seedling survival, biomass, and distribution on Currituck Bank,
      North Carolina. Castanea. 52(2): 77-86.

Wunderlin, R.P. 1982. Guide to the vascular plants of central Florida. University
      Presses of Florida, University of South Florida. Tampa, FL. 472 pp.


Report by:  K. Hill, Smithsonian Marine Station
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Page last updated: Oct. 19,  2001