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
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
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.
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).
Sea oats is perhaps the most abundant plant of
beach dune communities (Sylvia 1986; Hester and Mendelssohn 1989, 1991; Bachman
and Whitwell 1995).
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
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).
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).
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
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
May compete with other salt-tolerant coastal
species; however, U. paniculata is the dominant species on foredunes and
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.
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
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
VI. SPECIAL STATUS
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).
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.
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of the Gulf and Atlantic Coasts from Louisiana to
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mycorrhizal fungi associated with Uniola
paniculata in Florida foredunes.
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Report by: K. Hill, Smithsonian Marine Station
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Page last updated: Oct. 19, 2001