The primary pollinators of I. pes-caprae appear to be Xylocopa species (large carpenter bees) which can disperse pollen up to 90 meters (Devall and Thien 1992). In observations and experiments carried out by Devall and Thien (1989), at least 30 species of hymenopterans (ants, bees, and wasps) were recorded visiting I. pes-caprae flowers, but most of these were rarely encountered. The principal insect visitors--Xylocopa brasilianorum, X. strandi, Agapostemon nasutus, and Apis mellifera--differed significantly in their ability to pollinate I. pes-caprae. Xylocopa brasilianorum was the principal pollinator, as 44 of its 72 visits resulted in fruit set, and together the two species of Xylocopa carried out 49.5% of the pollination. Agapostemon nasutus pollinated 22.7% of the flowers. Although A. mellifera visited frequently, it had a low rate of succesful pollination (12%). Other insects did not visit frequently enough to be included in the analysis. Ants and butterflies visited a few flowers, but fruit set never resulted. The bruchid beetle Megacerus leucospilus was found visiting only three flowers, but two of those vists resulted in fruit set (Devall and Thien 1989).
In total, Devall and Thien (1989) collected 54 insect species from I. pes-caprae flowers, extrafloral nectaries, and seeds on the south Gulf coast, and 31 species on the north coast. Only four species---Megacerus leucospilus (a bruchid beetle), Campsomeris tolteca (a scoliid wasp), Solenopsis geminata (an ant), and Apis mellifera (honey bee)--were collected on both north and south Gulf coasts, but congeneric ant and bee species were present around the Gulf of Mexico.
Ipomoea pes-caprae subspecies brasiliensis is a pantropical, perennial, trailing vine, often forms large mats just above the high tide line on coastal beaches and dunes throughout tropical and subtropical regions of the world. The long stems are purple and often root at the nodes. Showy, bisexual, funnel-shaped flowers are produced that have copious nectar from a large circular nectary at the base of the flower and smaller amounts from glands on the sepals. Insect visitors are attracted to the large flowers, which are produced year-round, by the pink-purple color and ultraviolet light patterns of the corolla; there is no notable floral odor. The plants are self-incompatible, outcrossing to produce seeds that are apparently dispersed by seawater (but see Martinez et al. 2002). The leaves are somewhat succulent (like those of many beach plants) and are usually at least slightly notched--like the cloven hooves of a goat ("pes-caprae" refers to goat feet). The plant's notched leaves produce nectar from a pair of glands on each petiole near the point of blade attachment. Red nectaries on young leaves attract ants and various other visitors; black nectaries on older leaves do not attract insects. (Jones and Kobayashi 1969; Devall and Thien 1989 and references therein; Whistler 1992; Kaplan 1999) Devall (1992) provides a comprehensive review of the biology of this plant and should be referred to for additional information.
Ipomoea pes-caprae occurs on the coastal beaches of 5 continents and most tropical islands, as well as on warm temperate shores (St. John 1970, cited in Devall 1992).
Ipomoea pes-caprae subsp. brasiliensis is common in the tropics (Liogier 1995).
Ipomoea pes-caprae is found throughout the tropics. It occurs on all the major high archipelagoes of Polynesia and all the low and high archipelagoes of Micronesia. It is among the most abundant species on rocky and sandy beaches of high islands, sometimes forming almost pure stands, but is uncommon on atolls. (Whistler 1992)
Ipomoea pes-caprae extends to roughly 30o north and 30o south latitudes. Its northern and southern limits appear to be directly determined by climate. (Devall 1992)
Ipomoea pes-caprae subsp. brasiliensis grows on sandy beaches throughout the tropics, its creeping stems extending almost to the hight tide mark (Whistler 1992). It may sometimes occur in the interior as well (Jones and Kobayashi 1969; Devall and Thien 2005 and references therein).
Ipomoea pes-caprae is common on limestone and unconsolidated beaches, on calcareous sand, and on gravel (Devall and Thien 1992).
Ipomoea pes-caprae subsp. brasiliensis is a trailing glabrous (smooth) vine with purple stems that often root at the nodes. The fleshy oblong to suborbicular leaves are 3 to 10 cm long and notched at the tip. They are simple and alternately arranged. Flowers are axillary, solitary or in few-flowered cymes up to 15 cm long. The calyx has 5 unequal, ovate to elliptic sepals 8 to 13 mm long. The corolla is funnel-shaped, pink to rose-purple, 3 to 5 cm long, and shallowly 10-lobed. There are 5 stamens and the ovary is superior. The fruit is an ovoid to subglobose capsule, 12 to 17 mm long, containing 4 dark, ovoid, densely hairy seeds 6 to 10 mm long. (Whistler 1992)
Ipomoea pes-caprae subsp. brasiliensis is a prostrate, glabrous, somewhat succulent seashore plant. The stems contain a milky latex and may reach 20 meters in length. The oblong to rounded leaves have a long petiole (leaf stalk) and are slightly notched to shallowly bilobed. They are mucronate (i.e., ending in a sharp tip) at the apex and rounded to truncate or subcordate at the base, slightly leathery, and on the undersurface have a visible gland on each side at the base of the midrib. The inflorescence contains 1 to several flowers. Pedicels (flower stalks) are 2 to 5 cm long and slender. The sepals are obtuse or rounded at the apex and mucronate; the inner sepals are about 1 cm long, the 2 outer sepals are shorter. The fruit is an ovoid-globose capsule, 1.5 cm long that dehisces (naturally opens) into 4 valves.The capsule contains 4 densely dark brown pubescent seeds. (Liogier 1995)
Patino and Grace (2002) investigated the temperatures of flowers of Ipomoea pes-caprae subsp. brasiliensis in bright sunshine and carried out experiments to determine the role of the corolla (the collective term for the petals of a flower) and sepals in cooling the gynoecium (the female flower parts). Based on these studies, they concluded that the characteristic trumpet shape of the corolla is not merely an advertisement to attract insects but also a parasol or radiation shield to maintain the gynoecium at its functioning temperature. The structure has high reflectance and high conductance to water vapor. At the same time, there seems to be a balance between prevention of overheating and reduction of water loss by the corollas. Reduction of water loss may involve decrease of epidermal conductance (i.e. few stomata grouped in the corolla tube), low absorbed radiation, reduced evaporative surface (fused petals reduce the exposed surface area), and short-lived flowers (less than one day). Patino and Grace found that temperatures only slightly above those recorded in the natural environment caused death of pollen, and continued exposure to high temperatures resulted in damage to female reproductive tissue as well.
Devall and Thien (1989,1992) studied the reproductive biology of Ipomoea pes-caprae at several sites around the Gulf of Mexico. They confirmed the previous finding for this species from other regions indicating that it is self-incompatible, i.e., few or no viable seeds are produced by pollinating a flower using pollen from the same individual plant. They observed a lack of pollen tube growth associated with self-pollination. They found that this species exhibits a high pollen/ovule ratio, which is characteristic of obligately outcrossing plant species. The primary pollinators of this species are apparently Xylocopa bees, which can disperse pollen up to 90 meters. Devall and Thien (1989) suggested that this species has water-dispersed seeds that are capable of long-range dispersal in great numbers. Surprisingly, experiments carried out by Martinez et al. (2002) found that seeds were fully inhibited and died and rotted upon exposure to seawater. Martinez et al. suggest that, rather than dispersing mainly by seed, this colonizing beach and foredune species propagates vegetatively through the expansion of branches that are broken into fragments by storm waves, transported by water, and then washed onshore into new locations. Importantly, however, Martinez et al. acknowledge that certain aspects of their experiments may have failed to mimic natural conditions in important ways that could potentially explain the mortality of seeds exposed to seawater.
Devall and Thien (1989) found that peak flowering time for I. pes-caprae is July to September on the south Gulf coast and South Padre Island, TX, and July-August at Grand Isle, LA. Plants growing in protected spots began flowering in May on both the north and south Gulf coast. During peak flowering periods, more than 3,000 flowers occurred daily in the large populations at the five study sites (~ 1,600 m2 or larger). At all their study sites I. pes-caprae flowers opened at sunrise and closed by early afternoon; the corollas would drop off the following morning. Flowers opened later and closed earlier on cloudy days.
Shortly after anthesis (flower opening), stigmas were receptive to pollen and the flowers began producing nectar. Nectar was produced throughout the morning until noon, accumulating up to 5.7 ul of nectar. Though secretion continued until around 1 P.M., total accumulation generally decreased thereafter. The mean sucrose equivalents (mg solute per mg solution) varied from 37 to 44. (Devall and Thien 1989)
The primary pollinators of I. pes-caprae around the Gulf of Mexico were bees. Large Xylocopa bees were the most successful pollinators in Yucatan. They are probably important pollinators of I. pes-caprae in other parts of the world as well, where various Xylocopa species have been associated with I. pes-caprae. Agapostemon bees frequently visited I. pes-caprae flowers as well and compensated for lack of efficiency as pollinators by large numbers of flower visits (22.7% of the pollination). Other bee species visited infrequently, but nevertheless did pollinate I. pes-caprae flowers. Devall and Thien noted that the seed predator Megacerus leucospilus was also an efficient pollinator of I. pes-caprae, although it had a low frequency of visits. Ants and butterflies were not successful pollinators, probably because they could obtain nectar without touching the flower's reproductive parts.
Ipomoea pes-caprae includes two subspecies, brasiliensis and pes-caprae. The two subspecies differ in the shape of the leaves and the dimensions of calyx and corolla. Subspecies pes-caprae is confined to the Indian Ocean area, while subspecies brasiliensis is pantropical except in the Indian Ocean. (Devall 1992 and references therein)
Commenting on Ipomoea pes-caprae subsp. brasiliensis with respect to Polynesia, Whistler (1992) notes that although this vine is common and widespread, few uses are reported for it and it is often not even distinguished from other i.e., littoral (seashore-associated) vines by islanders. However, Devall cites reports of this plant being used in Bimini to treat strain, fatigue, and physical weakness; in French Guyana as a diuretic; in India to treat rheumatism; and in Nigeria to treat arthritis (references cited in Devall 1992).
