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Species Description:
Warea carteri is an erect annual herb
that grows to a height of approximately 0.2 - 1.5 m (7.9 inches
to 5 feet). Leaves measure 1 - 3 cm (0.4 - 1.2 inches) in
length, are simple, alternate, and lack stipules. Leaf shape
is spatulate or oblanceolate, but those nearer to the stem tip become
shorter, narrower and elliptical. Lower
leaves on the plant are typically lost before flowering begins.
Flowers are bourne on an inflorescence
in dense, rounded racemes of approximately 60 flowers.
Flowers are white in color and have 4 petals that are curved toward
the center of the flower. Petals measure approximately 4 -
6 mm (0.1 - 0.2 inches). Six stamens are subequal in length,
arising from a nectar-producing floral disc. Cylindrical ovaries
measure approximately 2 - 2.5 mm (0.08 - 0.1 inches) in length,
and are raised on a thin stalk (gynophore). Fruits are thin
seed pods called siliques that appear on short stalks and measure
4 - 6 cm (1.6 - 2.4 inches) in length (USFWS
1996; Kral
1983).
II.
HABITAT AND DISTRIBUTION
Regional Occurrence:
Currently, the only known populations of Warea carteri
occur in scrub habitats of the Lake Wales Ridge in Lake, Polk and
Highland Counties. It has historically been collected from
Dade and Brevard Counties as well; however, it has been extirpated
from Dade County and is possibly extirpated from Brevard County
(USFWS 1999).
IRL Distribution:
Coastal scrub areas of Brevard County are included in the historical
range of Warea carteri though there have been no recent
occurrences. The USFWS (1999) considers it likely extirpated
from the County, however, isolated populations may still exist.
III. LIFE HISTORY AND
POPULATION BIOLOGY
Age, Size, Lifespan:
Warea
carteri grows to a height of 0.2 - 1.5 m (7.9 inches to 5 feet).
Leaves measure 1 - 3 cm (0.4 - 1.2 inches) in length.
Petals measure approximately 4 - 6 mm (0.1 - 0.2 inches).
Ovaries measure approximately 2 - 2.5 mm (0.08 - 0.1 inches) in
length. Fruits measure 4 - 6 cm (1.6 - 2.4 inches) in
length (USFWS
1996; Kral
1983).
Abundance:
Carter's mustard is endemic to scrub habitats in Florida and has
been classified as Endangered since the late 1980s. It is
now found only on Lake Wales Ride in central Florida, but has a
historical range that included Brevard County and Miami-Dade county.
Present distributional records may be somewhat incomplete, however,
as the plant is relatively inconspicuous except when flowering (USFWS
1999).
Growth is
stimulated by infrequent fires, with large population increases
often observed in the year following a fire disturbance. Evans
et al. (2000) reported Warea carteri thrives in post disturbance
niches, and reported population size may increase as much as 3 orders
of magnitude following a fire, but decrease in the second year following
a fire. This pattern is indicative that a potentially large
seed bank may be present in soils.
Seeds stored under dark, dry conditions remained viable for at least
2 years under lab conditions (Evans et al 2000).
Human disturbed
areas sometimes have larger populations of Warea carteri
than undisturbed locations with disturbed populations tending to
be somewhat more stable over time (USFWS 1999; Evans et al. 2000).
Reproduction:
Carter's
mustard is self compatible and autogamous (self-fertilizing).
Natural fruit and seed set levels are relatively high, with fruit
sets of approximately 62% and seed sets of 50%. However, self-pollinated
flowers have reduced levels of fruit (41%) and seed set (28%), indictating
that insect pollinators are important to individual fecundity.
Important pollinators include a wide variety of insects including
bees, bee-flies, wasps, flies and beetles. Pollination most
often occurs within rather than among plants (USFWS 1999).
Anthers begin
to dehisce within several hours of flower opening, while stigmas
remain receptive 2-4 days after stamens have dropped from the flower.
Fruit is a silique, a thin, flattened seedpod, somewhat curved along
its length and measuring 8.5 mm (0.3 inches) in length. As
siliques dry, they split to disperse mature seeds. Seeds drop
passively to the ground, or are dispersed slightly farther away
from the parent plant if silques are brushed.
Genetic variation is lower in Warea
carteri than in other species with similar ecological and life
history traits (Evens et al 2000) with 6.6% of loci polymorphic
within populations. Most genetic diversity was observed among
rather than within populations.
Embryology:
Seed germination requires
both moisture and light, and occurs from approximately January through
March. Flowering begins in September and lasts through October,
with fruiting following from October through November. Seed
dispersal occurs in December (Kral 1983).
Seedling mortality is greatest during the
drier months of April and May. Plants that survive spring
drought often begin doubling in height monthly once rains begin
in June (ABS 2006).
IV. PHYSICAL TOLERANCES
V. COMMUNITY ECOLOGY
Habitats:
Warea carteri occurs in xeric
scrub, oak hammock, scrubby-flatwoods, oak sandhills, or in ecotones
between habitat types. It is often found in or in close proximity
to yellow sands. In disturbed scrub areas, it is found found
along ditches and roadsides. The 2 largest populations currently
in existence occur in yellow-sand scrub, scrubby flatwoods, and
in turkey oak-hickory sandhills at Archbold Biological Station and
The Nature Conservancy's Tiger Creek Preserve, both on the Lake
Wales Ridge (USFWS
1999).
Warea carteri has
also been collected from coastal scrub in Brevard County, but not
recently. Before its extirpation from Dade County, it occurred
in scrub and slash pine communities (USFWS 1999).
This species is fire-associated, with increased
emergence of new plants occurring in the year following a fire disturbance
(USFWS 1999).
VI. SPECIAL STATUS
Special Status:
Warea carteri has been listed federally
as an Endangered species since January 21, 1987 as the result of
habitat loss. The State of Florida lists it as Endangered.
The
primary threats to the continued existence of Carter's mustard are
habitat destruction by human development and fire suppression.
At least 2/3 of south-central Florida's sand pine scrub community
has been cleared for housing, roads, and citrus groves (Peroni
and Abrahamson 1985; Christman 1988). Additionally, fire suppression
over long periods likely destroys seed banks, resulting in subsequent
population declines.
The U.S. Fish and Wildlife
Service recovery plan for Warea carteri states that the
immediate recovery goal is to stabilize populations from further
decline. The overall population will be considered stable
when existing populations within the historic range are adequately
protected from further habitat loss and fire suppression; and when
existing sites are managed to maintain scrubby flatwoods, and turkey
oak dominated high pine areas.
Once populations have stabilized,
and enough demographic data are available to determine the optimum
population size that will assure a 95% probability of species survival
for 100 years, Warea carteri will be considered for reclassification.
Management activities being
undertaken at present include determining the current distribution
of Warea carteri by thoroughly surveying areas of the historic
range, including Brevard County; regional and local planning to
protect existing plants and habitat; purchasing privately held lands
where Warea carteri occurs; granting conservation easements
or entering into other landowner agreements to protect existing
plants; prescribed burning; elimination of exotic and invasive vegetation;
controlling access to areas when plants grow; conservation
of germ plasm in long-term storage; increased enforcement of existing
protection measures (over-collecting, off road vehicles use, etc);
life history and ecological research; and public outreach to raise
public awareness of the importance of the scrub community and its
unique biota (USFWS 1999).
VII.
REFERENCES
Archbold Biological Station
(ABS). 2006. Plant species account for Warea carteri.
Accessed online: www.archbold-station.org/abs/plantspp/waecarsppacc.htm.
Christman, S. 1988. Endemism
and Florida's interior sand pine scrub. Final
project report, Project No. GFC-84-101.
Submitted to Florida Game and
Fresh Water Fish Commission, Tallahassee,
237 pp.
Evans, M., R. Dolan, E.
Menges, and D. Gordon. 2000. Genetic diversity and
reproductive biology in Warea carteri
(Brassicaceae), a narrowly endemic
Florida scrub annual. American Journal
of Botany 87(3):372-381.
Kral, R. 1983. A report
on some rare, threatened or endangered forest-
related vascular plants of the South. USDA
Forest Service, Technical Publication
R8-TP2. 1305 pp.
Menges, E.S., and D.R.Gordon.
1996. Three levels of monitoring intensity
for rare plant species. Natural Areas
Journal 16:227-237.
Nauman, C.E. 1980. Status
report on Warea carteri. Unpublished report prepared
for U.S. Fish and Wildlife Service. 24
pp.
Peroni, P.A. and W.G. Abrahamson.
1985. A rapid method for
determining losses of native vegetation.
Natural Areas Journal
5: 20-24.
U.S. Fish and Wildlife Service(USFWS).
1999. South Florida multi-species
recovery plan. Atlanta, GA.
2,172 pp.
U.S. Fish and Wildlife Service(USFWS).
1996. Recovery plan for nineteen
Florida scrub and high pineland species
(Revised). U.S. Fish and Wildlife
Service; Atlanta, GA.
Wunderlin, R.P. 1982. Guide
to the Vascular Flora of Central Florida. University
Presses of Florida, Gainesville. 472 pp.
Report by:
K. Hill, Smithsonian Marine Station
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Page last updated: July 11, 2006 |
