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Species Name:    Polygala smallii
Common Name:          Tiny Polygala

 

I.  TAXONOMY

Kingdom Phylum/Division: Class: Order: Family: Genus:
Plantae Magnoliophyta Magnoliopsida Polygales Polygalaceae Polygala

Polygala smallii in flower.  Photo by D. Duval, courtesy of U.S. Fish and Wildlife Service.

Species Name: 
Polygala smallii R.R. Small and Ward

Common Name:
Tiny polygala, tiny milkwort.

Synonymy:
Polygala arenicola Small, non Guerke; Pylostachya arenicola Small

Other Taxonomic Groupings:
Subclass: Rosidae

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