Conservation Action Plan
Okenia hypogaea
Species Name: Okenia hypogaea Schlect. & Cham.
Common Name(s): beach peanut, burrowing four-o’clock, dune groundnut, Mexican
beach peanut
Synonym(s): none
Family: Nyctaginaceae
Species/taxon description: Annual herb, stems and branches prostrate, to 2 m. Leaves
opposite, fleshy, ovate with crenate dark purplish-pink margins, green above, silverygreen below, conspicuously ribbed, sometimes clustered at nodes, sometimes very
unequal in size, usually to 4 cm but occasionally to 8 cm. Leaves and stems sticky with
stiff glandular hairs, often becoming coated with sand. Petioles equal leaves in length.
Showy, solitary reddish-purple flowers borne erect on short pedicels from leaf axils;
petals absent; calyx reddish purple, about 3 cm across, with 5 notched lobes. Stamens
18 or less, with filaments white at the base, magenta above. Anthers pale yellow, 2lobed. Flower stalk elongates after fruit begins to form and pushes the fruit under the
sand as much as 15 cm. Fruit are ellipsoid, to 1 cm (0.4 in) long, whitish, often with a
single seed. Taproots are deep, stout, and give rise to many stems (Austin et al. 1991,
Coile 2000, Small 1919, Ward 1979, Wunderlin 1982).
To the untrained eye, O. hypogaea looks very similar to Boerhavia diffusa, a common
herb that is also in the Nyctaginaceae and can be found along dunes. The two species
are easy to tell apart when flowering, as O. hypogaea has much larger, solitary flowers.
When vegetative, the dense pubescence of O. hypogaea stems can aid in differentiating
the two.
Legal Status: Florida endangered, Imperiled (IRC, FNAI)
Biogeographic Value: Native
Prepared by: Jennifer Possley and Meghan Fellows, Samuel J. Wright, Conservation
of South Florida Endangered and Threatened Flora (ETFLORA) Project, Research
Department, Fairchild Tropical Garden
Last Updated: September 2002 (Possley and Fellows), October 2003 (Wright), April
2004 (Wright).
C. Lane
Background and Current Status
Range-wide distribution – past and present
Florida: (confidential)
World: (confidential)
Population and reproductive biology/life history
Annual/Perennial: Annual (Iverson 2004, Coile 2000, Ward 1979, Small 1919)
Habit: Prostrate herb
Short/Long-Lived: Short-lived, plants tend to disappear over the winter (Austin et al.
1991, Wright pers. obs.)
Pollinators: Flowers visited by bee, butterflies, wasp, and fly (Iverson 2004). Skipper
moths have been observed visiting the flowers (Wright per. obs.)
Flowering Period: Occasional all year but heaviest late spring through early fall
(Fairchild). Summer and fall (Wunderlin 1982). April-November (Taylor 2000).
Fruiting: Summer and fall (Fairchild)
Annual variability in Flowering: J.K. Small (1919) writes “there seems to be no
regular season for it, plants and colonies appearing according to the times the fruits
ripen and the local conditions favorable to their sprouting.”
Germination Period: “In some years, a few seeds germinate and even flower during
fall and winter, but these are unlikely to survive until the summer growing season. For
most of the population, germination begins from early March to June.” (Iverson 2004)
Growth Period: Spring and summer (Fairchild)
Dispersal: Water (Austin et al. 1991). Winter storms may excavate the fruit; deposit it
at the upper limit of the storm swell, where they germinate the following spring
(Iverson 2004). Seeds can float for several hours in salt water (Iverson unpub. data).
Seed Maturation Period: unknown
Seed Production: unknown, although during a recent collection of seeds for a seed
germination study, 90 mature seeds were harvested in a 30.5cm2 area of the dune
(Wright 2003). One seeded fruit (peanut).
Seed Viability: In-field studies have shown a 32% (n = 200) germination rate. Seeds
may remain viable in the soil for a number of years. Seedlings germinated in an area of
site 102 that has not had O. hypogaea plants in over 5 years (Fernandez pers. comm.).
Seeds of fruit harvested in February germinated at a higher percentage (22%) than those
harvested in December (1.6%) (Fisher unpublished).
Regularity of Establishment: unknown
Germination Requirements: Though not a requirement O. hypogaea, may benefit
from disturbance (e.g. hurricane). Increased germination and flowering have been
observed (Wright per. obs.) on three separate occasions after anthropogenic events
(filming of a music video, removal of invasive plants, and widening of a crossover dune
foot trail). Increased out of season germination observed after low intensity 2003 arson
fire (Wright, Maschinski per. obs.) Seeds do not need light to germinate (Fisher
unpublished).
Establishment Requirements: Seedlings do not survive unless buried at least 5 cm (2
in) deep (Iverson 1984, as cited in Johnson and Barbour 1990). Fruits require at least 45cm of burial by sand for growth (Iverson 2004), however germination or seedling
emergence are not affected by planting depth between 1 and 12m (Fisher unpublished).
Population Size: Austin et al. (1991) indicated populations may be increasing in size,
however, Fairchild monitoring does not show this to be the case: a Florida Department
of Environmental Protection survey of Site 6 in 2002 located 13 colonies on site, while
a 2003 survey located only 3 colonies (J.A. Duquesnel, unpub. data). O. hypogaea “may
have expanded its Florida range while simultaneously losing its habitat to mankind.”
(Iverson 2004)
Annual Variation: Because O. hypogaea senesces after fruiting, populations give the
appearance of great annual variation, but actual variation is unknown.
Number and Distribution of Populations: (confidential)
Habitat description and ecology
Type: COASTAL DUNE. Beach dunes and coastal hammocks (Taylor 1998). Ocean
side of coastal dunes (Coile 2000). Coastal hammocks and beaches (Wunderlin 1982).
Also occasionally found under Casuarina equisetifolia (Australian pine), along the
intra-coastal waterway, or disturbed coastal sites (Iverson 2004).
Physical Features:
Soil: Sand or other loose, well-drained soils. (Iverson 2004).
Elevation: Low
Aspect: unknown
Slope: often accumulates its own “dunelet” (Austin et al. 1991)
Moisture: sand is moist at the level of buried seeds (Iverson 2004) and may
facilitate germination
Light: full to partial sun
Biotic Features:
Community: COASTAL DUNE. Seaward side of sand dunes in the pioneer
zone commonly associated with Ipomoea pes-caprae ssp. brasiliensis (railroad
vine), Sesuvium portulacastrum (sea purslane), Cyperus pedunculatus, (beach
star) and Panicum amarum (bitter panicgrass). Occasionally found more inland,
in disturbed coastal strand communities. In such cases, associated plants noted
by Fairchild have been C. equisetifolia, Bidens alba var. radiata (Spanish
needle), Dactyloctenium aegyptium (Durban crowfoot grass), and other grasses.
Interactions:
Competition: after initial succession into an open area O. hypogaea
tends to be outcompeted by grasses and shrubs (Wright pers. obs.)
Mutualism: unknown
Parasitism: n/a
Host: n/a
Other: unknown
Animal use: unknown
Natural Disturbance:
Fire: Unknown, although an estimated 5000 seedlings germinated out of season
(late November) in response to a 2003 arson fire at Site 102 (Maschinski unpub.
data).
Hurricane: Unknown, although O. hypogaea seems to respond well to lowscale disturbance. Seed dispersal and habitat opening from hurricanes could be
beneficial. O. hypogaea is uniquely adapted to beaches annually reshaped by
storms (Iverson 2004)
Slope Movement: Sand stabilizer (Austin et al. 1991). Will tolerate burial by
sand (Fairchild), frequently reappears after sand moving/replenishing (Paul
Davis, Palm Beach County Environmental Resources Management, per.
comm.).
Small Scale (i.e. Animal Digging): Shares habitat with nesting Loggerhead sea
turtles (Caretta caretta), but the affects of digging are unknown. Disturbance
from digging may help facilitate dispersal and/or germination.
Protection and management
Summary: The range of O. hypogaea in Florida consists of both protected and nonprotected sites. There is a wide spectrum of management practices on protected sites,
which range from nearly pristine dunes to beaches that are subject to heavy foot traffic,
raked free of oceanic debris. These generally lack dune structure. While threat of
extinction doesn’t appear imminent within the next 5 years, its ephemeral nature and
continued habitat pressure warrant monitoring.
Availability of source for outplanting: (confidential)
Availability of habitat for outplanting: (confidential)
Threats/limiting factors
Natural:
Herbivory: unknown
Disease: unknown
Predators: unknown
Succession: Overgrowth of Coccoloba uvifera (seagrape) can reduce available
habitat, as can graminoids and herbs (Fairchild). On the other hand O. hypogaea
is a pioneer species and shading out of it by native grasses and herbs may be the
natural succession of the dune habitat
Weed invasion: Non-native invaders of coastal dunes such as Wedelia trilobata
(creeping oxeye), D. aegyptium, Catharanthus roseus (Madagascar periwinkle)
and Scaevola sericea (beach naupaka) pose threats. C. equisetifolia invades O.
hypogaea habitat at many sites, mostly in areas where foredune vegetation is
pushed back west because of beach raking. O. hypogaea appears to be able to
survive under the thick duff produced by these trees, but this may be only in
instances where human foot traffic or vehicles disturb the duff layer frequently
(Fairchild). One site in north Palm Beach County had O. hypogaea reported as
being under Casuarina duff in the 1990s, but Fairchild could not locate any
plants, indicating that the population may not have survived.
Fire: Effects of fire on plants are unknown although O. hypogaea could
colonize areas opened up by fire if fruits were to survive. Fire disturbed areas
could also help to facilitate fruit germination as was observed after the arson fire
at Site 102.
Genetic: unknown
Anthropogenic
On site: Destruction of dune habitat for development is the primary threat
(Ward 1979, Iverson 2004). One population in Boca Raton was lost to
development in the late 1990s (F. Griffiths, Palm Beach County Environmental
Resources Mgmt, per. comm.). Beach raking and recreational sports are also
significant, destroying plants at the seaward dune edge (Iverson 2004).
Trampling by sunbathers may also have a significant effect on establishment.
Fires could start from barbecues pits (which are commonly stationed under
Casuarina in parks) and reduce portions of the population that are in the same
location. Plants may be mistaken for a weed and be removed or sprayed with
herbicide by maintenance personnel. Fairchild witnessed sod pieces being laid
over O. hypogaea plants at one site.
Off site: Off-site jetties, inlets or seawalls may cause loss or increase of
shoreline thereby effecting natural environmental influences such as wind, salt
spray and tidal influences. These coastal structures could cause coastal erosion
by trapping sand that would otherwise naturally replenish beaches inhibiting
establishment.
Collaborators
Steve Bass, City of Boca Raton
Paul Davis, Palm Beach County, Environmental Resources Management
Janice A. Duquesnel, State of Florida
Liz Golden, State of Florida
Frank Griffiths, Palm Beach County, Environmental Resources Management
Juan Fernandez, City of Miami
Grace Iverson, Martin County researcher
Joe Maguire, Miami-Dade County, Natural Areas Management
Ernie Lynk, Miami-Dade County, Parks and Recreation, Crandon Park
Richard Moyroud, Native Plant Society, Mesozoic Landscapes Inc.
Conservation measures and actions required
Research history:
Martin County researcher Grace Iverson conducted research on establishment
and germination (Iverson 1980-1987).
Fairchild began monitoring and mapping O. hypogaea in 2001-2002. Possley
surveyed every publicly owned coastal park from Miami-Dade County to Martin
County and located O. hypogaea at 19 sites (Possley 2002).
No plants were observed during a survey of Site 132 on November 14, 2001. A
voucher specimen was collected there in 1970 by William T. Gillis.
Population maps have been created for the newly discovered 2003 colonies at
Site 102 and Site 23.
Fairchild is currently monitoring a project to study the seed germination and
seedling survival rates of O. hypogaea. Fairchild is also in the process of researching
the relationship of mycorrhizae with O. hypogaea.
Fairchild is currently monitoring the survival rate of germinated seedlings with a
burn area.
Fairchild staff visited Site 156 in January 2004 and observed no plants. Due to
the timing, plants may have been dormant.
Significance/Potential for anthropogenic use:
- May have use as a source of starch from the flour of O. hypogaea seeds (Bello-Perez
et al. 2001)
- Dune stabilizer during the growing season. O. hypogaea and other pioneer species if
utilized in beach renourishment projects may greatly reduce shoreline erosion.
- Extremely showy flowers give this species a potential horticultural interest.
Recovery objectives and criteria: There are no federally established recovery goals or
criteria for this species.
Management options:
Continue Monitoring:
Annual or biannual monitoring will be useful to show any change in population size or
range. Monitoring should be done in coordination with existing monitoring occurring on
other nearby sites.
Conduct augmentations and/or reintroductions:
Because this species is not extremely rare within its (very rare) habitat, outplanting is
probably not warranted at this time. However, O. hypogaea should be considered as a
component in dune revegetation studies or as part of mitigation requirements.
Next Steps:
Continue monitoring.
Resurvey sites where plants were historically present (Hammer 1996).
Continually update south Florida site map for presence/absence based on surveys.
Determine northern and southern extent of current range in Florida.
Investigate ecological questions such as response to fire, light, salinity, inundation, or
dormancy.
Investigate relationship with mycorrhizae.
Report occurrence information to FNAI
References
Austin, D., P.N. Honeychurch, and S. Bass. 1991. Coastal dune plants. Published by
Gumbo Limbo Nature Center of South Palm Beach County, Inc.
Bello-Perez, L.A., J. Solorza-Feria, M.L. Arenas-Ocampo, A. Jimenez-Aparicio and M.
Valazquez del Valle. 2001. Chemical composition of Okenia hypogaea seed (Schl. and
Cham). Agrociencia 35: 459-468
Coile, N.C. 2000. Notes on Florida’s Endangered and Threatened Plants. Florida
Department of Agriculture and Consumer Services, Division of Plant Industry, and
Bureau of Entomology, Nematology and Plant Pathology, Botany Section. Contribution
No. 38, 3rd edition.
Hammer, R.L. 1996. Checklist of vascular plants (draft), Alice Wainwright Park, 2845
Brickell Ave, Coconut Grove, Dade County, Florida. May 1996.
Iverson, G.B. 1980-1987. Unpublished ecological study of Okenia hypogaea at
MacArthur Beach State Park, Palm Beach County and northern Broward County.
Iverson, G.B. 1984. Ecological adaptation of beach peanut (Okenia hypogaea) on
Florida subtropical east coast beaches. Fla. Sci. 47, 45 (Abstract)
Iverson, G.B. 2004. Endangered burrowing four-o’clock. In: K. Burks, ed. Rare and
Endangered Biota of Florida, Volume 5: Plants. University Presses of Florida,
Gainesville, Florida. (in press)
Johnson, A.F. and M.G. Barbour. 1990. Dunes and Maritime Forests. Pages 429-480 in
R.L. Myers and J.J. Ewel (eds.) Ecosystems of Florida. University of Central Florida
Press, Orlando. 765 pp.
Possley, J. 2002. Conservation Action Plan: Okenia hypogaea. In Maschinski, J.,
M.Q.N. Fellows, J. Possley. 2002. Conservation of South Florida Endangered and
Threatened Flora. Final Report to the Endangered Plant Advisory Council, Florida
Department of Agriculture and Consumer Services, FDACS Contract # 006466.
Schlechtendal and Chamisso. 1830. Okenia hypogaea. Linnaea 5:92.
Small, J.K. 1919. Okenia hypogaea. Addisonia 4:11-12.
Taylor, W.K. 1998. Florida Wildflowers in their natural communities. University Press
of Florida, Gainesville.
Ward, D.B. 1979. Endangered burrowing four-o’clock. In: D.B. Ward, ed. Rare and
Endangered Biota of Florida, Volume 5: Plants. University Presses of Florida,
Gainesville, Florida. 175 pp.
Wright, S.J. 2003. Okenia hypogaea Schltdl. & Cham. In Maschinski, J., S. J. Wright,
K. Wendelberger, H. Thornton, A. Muir. 2003. Conservation of South Florida
Endangered and Threatened Flora. Final Report to Florida Department of Agriculture
and Consumer Services. Contract #007182.
Wunderlin, R.P. 1982. Guide to the Vascular Plants of Central Florida. University
Presses of Florida. Tampa, Florida. 472 pp.
Electronic References
http://eebweb.arizona.edu/Herb/riomayo/p8.html
http://www.ceprobi.ipn.mx/Proyectos/conacyt/CONACyT2031514B.htm
http://www.csdl.tamu.edu/FLORA/b98/bonogen.htm
http://www.ine.gob.mx/ucanp/data/programasmanejo/islacontoy/presentacion.html
http://www.plantatlas.usf.edu/source.asp?plantID=766
http://www.regionalconservation.org/ircs/database/plants/PlantPage.cfm?TXCODE=Ok
enhypo