Species Description: Ipomoea pes-caprae, commonly referred to as railroad vine, is a pantropical, trailing vine that routinely colonizes sand dunes. It grows just above the high tide line along coastal beaches, forming large mats that assist in stabilizing sands. Runners are succulent and have a milky colored sap. Branches may reach 10 m (approximately 33 feet) in length. Leaf petioles are 1.5 - 1.6 mm (approximately 0.06 inches) long, with leaf blades measuring approximately 3-14 cm (1.2 - 5.5 inches) in length, 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 1992).
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 (Devall 1992).
Potentially Misidentified Species: Canavalia rosea (Bay bean)
Regional Occurrence: 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.
IRL Distribution: Railroad vine occurs throughout the Indian River Lagoon on coastal dunes, scrub and some upland areas.
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.
Abundance: 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).
Reproduction: 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).
Embryology: 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).
Temperature: 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 1992).
Railroad vine survives soil temperatures on coastal beaches that often exceed 40° C (104° F).
Salinity: 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 1992).
Physical Tolerances: 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.
Trophic Mode: Autotrophic.
Competitors: 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.
Habitats: Railroad vine has a pantropical distribution over a variety of habitats, its distribution undoubtedly aided by buoyant seeds that drift in the sea and ensure 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.
Associated 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.
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 prevent erosion.
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).
Economic Importance: 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. Ecological Entomology 23:238-245.
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): 1821-1831.
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. 45: 495-497.
St. John, H. 1970. Classification and distribution of the Ipomoea pes-caprae group (Convolvulacea). Botanische Jahrbucher Systematik 89:563-583.