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Species Description:
Polygala smallii is a short-lived,
herbaceous member of the milkwort family. This erect plant
typically grows no taller than 8 cm (3.1 inches) in height (Kennedy
1998) and forms rosettes of 1 - 4 unbranched stems. The taproot
is well developed and scented. Leaves are oblanceolate to
lanceolate in shape and measure approximately 1.5 - 5 cm (0.6 -
2.0 inches) in length, and 0.2 - 1.4 cm (0.08 - 0.6 inches) in width.
Asymmetrical yellow flowers appear on cylindrical racemes that measure
0.4 - 7 cm (0.2 - 2.8 inches) in length. Each flower has 5
sepals, with the lateral pair large and petaloid. Corollas
are greenish-yellow and bear 3 petals. Fruit is a 2-celled
capsule that opens along the center to reveal a seed 1.2 - 1.4 mm
(0.05 - 0.06 inches) in length, covered in short, stiff hairs (Gann
and Bradley 1995; USFWS 1999).
II. HABITAT AND DISTRIBUTION
Regional Occurrence:
Polygala
smallii is endemic
to east-central Florida from southern St. Lucie County through Miami-Dade
County. Only 11 documented populations are documented to occur,
all of which are found within 10 km (6.2 miles) of the Atlantic
coast. Seven of the existing populations currently occur on
managed public lands (USFWS 1999).
Historically, the northernmost extent
of the range was believed to be Broward County, but more recent
survey efforts have extended the range into southern St. Lucie county.
Polygala smallii may have occurred as far north as Brevard
County, but this is uncertain, as the only evidence is a single
specimen collected in 1874 labeled "Indian River" (USFWS
1999).
IRL Distribution:
Within IRL Counties, Polygala smallii occurs within 10
km (6.2 miles) of the coast in Palm Beach, Martin and southern St.
Lucie Counties (USFWS 1999).
III. LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan:
Tiny polygala reaches a height of
approximately 8 cm, with leaves measuring
approximately
1.5 - 5 cm (0.6
- 2.0 inches) in length, and
0.2 - 1.4 cm (0.08
- 0.6 inches) in width (USFWS
1999).
Abundance:
Polygala smallii is a rare, endemic plant with only 11
known populations. It has been federally
listed as an endangered species since July 1985 (USFWS 1999),
and is listed by the State of Florida as Endangered.
Reproduction:
In
South Florida, populations of tiny polygala flower and produce seeds
throughout the year. There are 2 germination periods: a brief
one in June, and a prolonged one that occurs September - January.
Thus, generations may overlap within years, and plants mature at
varying times throughout the year (USFWS 1999).
Plants in their second year of growth begin
to show signs of poor condition, apparently to allocate energy to
flowering rather than growth or maintenance. By 18 months
of age, plants typically senesce and die (Miami Dade County 1994).
Pollination mode is unknown in Polygala
smallii (Miami-Dade County 1994; Kennedy 1998), but evidence
suggests it may be self-pollinating. Zomlefer (1991) reported
that tuft hairs on the apical lobes of flowers catch pollen from
dehiscing anthers and may transfer it to the stigma.
Embryology:
Seeds of Polygala smallii
exhibit both innate and conditional dormancy. Fresh seeds
of tiny polygala take approximately 2 - 3 weeks to overcome the
innate dormancy period, regardless of soil temperature. Seeds
at the soil surface never become conditionally dormant, with most
germinating from September through January. However, when
seeds are buried, some become conditionally dormant in the winter
months, meaning they remain viable but do not germinate, thus preventing
germination during unfavorable periods.
Ants are a likely vector for seed
dispersal in tiny polygala. Seeds have paired, fleshy outgrowths
called arils that are attractive to ants. Kennedy (1998) reported
observing ants transporting seeds by their arils from tiny polygala
flowers to their nests nearby. It had been suggested the arils
were actually lipid-rich elaisomes on which ants feed. However,
closer inspection of seeds by Kennedy (1998) determined the arils
were hollow sacs. It remains unclear why ants are attracted
to them (USFWS 1999).
Kennedy (1998) also suggested rivers
and streams as major transport vectors for tiny Polygala seeds,
reporting that hairs on the seeds trap ai, allowing seeds to float
on water for as long as 3 weeks.
Some evidence suggests that seed
banks may be vital to the population of Polygala smallii.
Following Hurricane Andrew in 1992, new emergence of tiny
polygala in areas where trees had uprooted or soils had overturned
was observed, indicating the presence of seed banks. In one
instance, the storm surge of Hurricane Andrew washed over a population
of tiny polygala near Biscayne Bay. The population subsequently
grew from 3 plants to 12 the following year (Miami-Dade County 1994).
Kennedy (1998) reported that buried
seeds in natural populations remained viable for an average of 2
years and had approximately the same germination success as freshly
produced seeds, indicating that seeds may actually remain viable
for decades as long as they are buried.
IV. PHYSICAL TOLERANCES
V. COMMUNITY ECOLOGY
Associated Species:
In populations that occur in Palm Beach and Martin Counties, Polygala
smallii sometimes occurs with a congener, P. nana,
which is not known to occur farther south than Broward County (USFWS
1999).
The overstory canopy in the Miami-Dade County
population consists of South Florida slash pine (Pinus elliottii
var. densa), various oaks (Quercus spp.), and
tallow wood (Ximenia americana).
In Broward County, the overstory
is composed primarily of sand pines (Pinus clausa), with
an understory of various shrubs including oaks (Quercus
spp.), dwarf cabbage palms (Sabal etonia), rosemary (Conradina
spp.), grasses, and deer moss (Cladina spp.) (Gann and
Bradley 1995).
In Palm Beach County, the canopy consists
of sand live oak (Quercus geminata), tallow wood
(Ximenia americana), and pines. Understory species
include oaks (Quercus spp.), saw palmetto (Serenoa
repens), cocoaplum (Chrysobalanus spp.), silkgrass
(Paspalum graminifolia), and partridge pea (Chamaecrista
fasciculata) (Gann and Bradley 1995).
In Martin County, the canopy is
composed of turkey oak (Quercus laevis) and South Florida
slash pine (Pinus elliottii var. densa), or mixed
sand pines. The understory consists of various oaks (Quercus
spp.), herbs, and grasses (Gann and Bradley 1995).
In St. Lucie County, the canopy
consists of pines and live oak (Quercus virginiana).
Understory plants include saw palmetto (Serenoa
repens), staggerbush
(Lyonia spp.), oaks (Quercus app.), and grasses
(Gann and Bradley 1995).
Habitats:
Polygala smallii typically occurs
in sand pockets of sand pine scrub, pine rocklands, slash pine,
high pine, and well drained coastal scrub with high light levels
and little accumulation of leaf litter. All documented habitats
are xeric and prone to periodic
fire disturbance (Gann and Bradley 1995; USFWS 1999).
While pine rocklands, scrub, and other critical
habitat areas must be periodically burned to reduce accumulation
of organic litter, prevent exotic plant invasions, and prevent overshading
of the herbaceous understory, it is
unclear whether periodic burning specifically enhances growth of
Polygala smallii since it is short-lived with a shallow
root system that is killed when fires occur. Thus, seed banks
must repopulate areas following fires.
The Miami-Dade County Polygala smallii
population occurs primarily in pine rocklands, in sand deposits
at least 2.0 cm (0.8 inches) deep and having somewhat shallower
deposits of leaf litter than the surrounding habitat.
In Broward County, most populations occur
in sand pine scrub in St. Lucie fine sands of approximately 2.8
m (9.2 feet) elevation.
The Palm Beach County population is found
in scrubby flatwoods established on spoil dredged from the IRL before
the 1940s and having an elevation of approximately 1.2 m (3.9 feet)
with relatively little slope.
The Martin County population occurs on turkey
oak sandhills of Pomello sand with an elevation of 1.2 m (3.9 feet).
The St. Lucie County population occurs on
scrubby flatwoods in Hobe Sand soils with an elevation of 2 - 3
m (6.6 - 9.8 feet), sloping to mesic flatwoods and marsh areas.
VI. SPECIAL STATUS
Special Status:
Polygala smallii has been Federally
listed as Endangered since July 18, 1985; and is also designated
by the State of Florida as an Endangered species. Future survival
of the species is threatened by habitat loss and degradation from
development, fire suppression, and infestation by exotic species
of plants (USFWS 1999). It is likely that this species may
never reach population levels that would allow its reclassification
or downlisting (USFWS 1999). However, recovery objectives
for Polygala smallii are to prevent its extinction and
stabilize existing populations. Stability will be achieved
when existing populations within the historic range are adequately
protected from further habitat loss or degradation, exotic plant
invasion, and fire suppression. Management to maintain pine
rocklands, scrub and scrub flatwoods will continue to support recovery
of tiny polygala.
Seven of the 11 known populations of Polygala
smallii occur on public lands that are actively managed.
Two of the remaining four populations occur on privately held lands
that are being managed as preserves. Human-related threats
to actively managed populations include trampling by heavy foot
traffic and bicycles, trash dumping, and unauthorized take (USFWS
1999).
Specific management activities directed at
recovery of this species include: monitoring to further determine
the distribution and population status; protection of existing
populations; ex situ collection of Polygala smalli
and establishment of cultivated populations that could be used to
supplement natural populations; seed banking; identification
of appropriate sites for reintroduction; enforcement of current
protective measures including take prohibitions; continued
public education and outreach efforts regarding the importance of
scrub, sandhills, and coastal spoil habitats; prescribed burning;
elimination of human-caused habitat degradation; and control
of exotic species in critical habitat areas (USFWS 1999).
VII.
REFERENCES
Gann, G. and K. Bradley.
1995. Endangered species status survey: Polygala
smallii Smith and Ward. Tiny
Polygala. U.S. Fish and Wildlife Service,
Jacksonville, Florida.
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.
Miami-Dade County Department
of Environmental Resource Management.
1994. Annual Report. Endangered
pine rockland plant species recovery
project. Unpublished report prepared
for the U.S. Fish and Wildlife
Service, Jacksonville,
Florida.
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.
Zomlefer, W. 1991.
Flower Plants of Florida, a Guide to Common Families.
Biological Illustration, Inc. Gainesville,
Florida.
Report by:
K. Hill, Smithsonian Marine Station
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Page last updated: July 24, 2006 |
