2.5 – 12 cm (1 – 4.7 inches) in width. Foliage leaves are alternate,
somewhat elliptical, and have shallow notches at their apexes. Taproots are long
and deep, sometimes penetrating more than a meter into the substratum (Devall
Flowers are generally axillary, 3 – 16 cm (1.2 –
5.5 inches) in diameter, and either angular or flattened. Corollas are 3 – 6
cm (1.2 – 2.4 inches) in length and funnel-shaped. Color ranges from pink to
red-purple or violet. Color tends to be darker at the inside base of each flower
II. HABITAT AND
Ipomoea pes-caprae is one of the most widely
distributed beach plants throughout tropical and subtropical areas in the world.
It occurs along the beaches, coastal strands and tropical islands of tropical
North and South America, east central Africa, west central Africa, India, Asia,
and Australia. In North America, I. pes-caprae occurs from Florida, and
west through the Gulf of Mexico and the Bahamas. Its range extends from
approximately 30° North latitude to 30°
South latitude. The extent of these limits are directly determined by climate,
as I. pes-caprae does not tolerate prolonged frost conditions.
Railroad vine occurs throughout the Indian River
Lagoon on coastal dunes, scrub and some upland areas.
III. LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan:
Railroad vine branches may reach 10 m
(approximately 33 feet) in length. Leaf petioles are 1.5 – 1.6 mm
(approximately 0.06 inches) long. Leaf blades reach 3-14 cm (1.2 – 5.5 inches)
in length, 2.5 – 12 cm (1 – 4.7 inches) in width (Devall 1992). Flowers are
3 – 16 cm (1.2 – 5.5 inches) in diameter, with corollas 3 – 6 cm (1.2 –
2.4 inches) in length.
Ipomoea pes-caprae is one of the most common
dune plants in the tropics and subtropics. It is also common in scrub areas and
some upland areas (Devall 1992).
Railroad vine grows vegetatively by rooting from
stem cuttings. It also reproduces by seed. Flowers of railroad vine are
short-lived: blooming at sunrise, closing by mid-afternoon, and dropping off the
plant the following day. Plants growing in protected sunny areas begin flowering
in May. Peak flower production depends on location. Gulf of Mexico plants peak
from July through September; Louisiana plants peak July through August; and
Costa Rican plants peak July through November (Devall 1992).
This species is an obligate outcrosser, having evolved
self-incompatibility adaptations (Martin 1970; Devall 1992). Insects, attracted
to the large nectaries in the showy flowers of railroad vine, assist in cross
pollination. Primary pollinating species include bees, butterflies, moths,
flies, beetles, wasps, and ants (Devall 1992).
Fruit production in railroad vine is generally
high, but is affected by storm events, plant density and other factors (Devall
1992). Four seeds per fruit are produced. Seeds are brown in color and measure
approximately 6-10 mm in length (Devall 1992). Seeds do not require a dormant
period before sprouting. However, the seed coat is impermeable to water and must
first be abraded by sand before the seeds will germinate.
Around the Gulf of Mexico, germination occurs in all
seasons except winter (Devall 1992). Upon sprouting, seedlings have deeply lobed
cotyledons that closely resemble the mature morphology of the species. The
ability of seedlings to become established is dependent on the same factors that
affect parental plants: wave action that can easily uproot young seedlings;
accreting sands which can bury seedlings in a short time; and space competition
and shading by established plants (Devall 1992).
IV. PHYSICAL TOLERANCES
Railroad vine is temperature limited to tropical
and subtropical zones between 30° N and 30°
S latitudes. In some areas, the above-ground portions of the plant die off in
winter, leaving underground stems to sprout when conditions again become
favorable. In more protected areas, plants remain green throughout the winter (Devall
Railroad vine survives soil temperatures on coastal
beaches that often exceed 40° C (104°
Ipomoea pes-caprae survives well in beach
communities and remains green even when subject to salt spray and wave splash.
In addition, it is known to recover well following hurricanes and tropical
storms which sometimes inundate beach areas with sea water and heavy winds (Devall
Railroad vine, as a pantropical species, is well
adapted to high temperature conditions. It also thrives in both seasonally dry
areas, and in areas that receive heavy rains. For example, it is common in the
northern Yucatan peninsula which has a 7 month dry season. It is similarly
common in areas such as coastal Florida, where average annual rainfall totals
are approximately 142 cm (57 inches); Louisiana which receives 175 cm (70
inches); and Texas which receives 68 cm (27 inches) (Devall 1992). However, this
species does not survive on the desert coasts of Peru.
V. COMMUNITY ECOLOGY
Ipomoea pes-caprae probably competes for
space and light with other coastal species of plants. Devall (1992) suggested
that in Florida, when I. pes-caprae competes with I. stolonifera,
that I. pes-caprae is most commonly on the more unstable substratum.
Leaves and branches of railroad vine are protected from
herbivores due to secondary metabolites. Branches have a milk-colored latex in
the sap, while leaves produce a compound called indole alkaloid ergotamine (Jirawongse
et al. 1977) that protects the plant from most insects and large grazing mammals
such as horses and donkeys. Flowers, however, have no chemical defenses and are
routinely eaten by caterpillars, beetles, and grasshoppers.
Railroad vine has a pantropical distribution over a
variety of habitats, its distribution undoubtedly aided by buoyant seeds that
drift in the sea and insure widespread dispersal. It is most commonly found as a
pioneering species on tropical beaches, growing just above the high tide line.
It is also common in backdunes, scrub and some upland areas where it grows along
roadsides (Devall 1992). St. John (1970) speculated that I. pes-caprae
does not invade uplands naturally, but settles in these areas as seeds are
dispersed by wind-blown sands. Its upland distribution is limited not only by
wind dispersal, but also by shade effects from other upland species.
Railroad vine is closely associated with other dune
and coastal strand species such as sea oats (Uniola paniculata), sea purslane
(Sesuvium portulacastrum), seashore dropseed (Sporobolus
virginicus), live oak (Quercus virginiana), glasswort (Salicornia
spp.) sea grapes (Cocoloba uvifera), and others.
VI. SPECIAL STATUS
Benefit in IRL:
Ipomoea pes-caprae is an especially
important pioneering species along tropical coastlines. Its ability to stabilize
sand dunes is a first line of defense against damaging storms. Plants creep over
sand dunes, setting down adventitious roots, and eventually form large mats that
Broad Scale Cost/Benefit:
Besides its ecological importance, railroad vine is
also used in some parts of the world to treat fatigue, strain, arthritis and
rheumatism. Some cultures also use it as a diuretic (Devall 1992).
Ipomoea pes-caprae has no direct economic
importance. However, its usefulness in stabilizing sand dunes and preventing
coastal erosion could have substantial indirect economic benefits.
Bach, C.E. 1998. Interactive effects of herbivory and
sand burial on growth in a
tropical dune plant, Ipomoea pes-caprae.
Devall, M.S. 1992. The biological flora of coastal
dunes and wetlands. 2.
Ipomoea pes-caprae (L.)Roth. Journal of
Coastal Research 8(2): 442-456.
Devall, M.S. and L.B. Thien. 1989. Factors influencing
the reproductive success
of Ipomoea pes-caprae (Convolvulaceae)
around the Gulf of Mexico.
American Journal of Botany 76(12):
Devall, M.S., L.B. Thien, and W.J. Platt. 1991. The
ecology of Ipomoea
pes-caprae, a pantropical strand plant. In:
Proceedings of the Symposium on
Coastal Sand Dunes (September 13-14, 1990, Guelph,
Ontario). University of
Guelph, Guelph, Ontario, Canada. 471 pp.
Jirawongse, V., T. Pharadai, and P. Tantivatana. 1979.
The distribution of indole
alkaloids in certain genera of Convolvulaceae growing
in Thailand. Journal of
the National Research Council of Thailand. 9:17-24.
Johnson, A.F. and M.G. Barbour. 1990. Dunes and
maritime forests. IN: Myers,
R.L. and J.J. Ewel, eds. Ecosystems of Florida.
University of Central Florida,
Orlando, Florida. pp. 429-480.
Kane, M.E., K.T. Bird, and T.M. Lee. 1993. In vitro
propagation of Ipomoea
pes-caprae (Railroad vine). Journal of
Coastal Research 9(2):356-362.
Martin, F.W. 1970. Self and interspecific
incompatibility in the Convolvulaceae.
Botanical Gazette 131:139-144.
Morton, J.K. 1957. Sand dune formation on a tropical
shore. Journal of Ecology.
St. John, H. 1970. Classification and distribution of
the Ipomoea pes-caprae
group (Convolvulacea). Botanische Jahrbucher
Report by: K. Hill, Smithsonian Marine Station
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Page last updated: Oct. 24, 2001