Inflorescence morphology, phenology, and pollination of the ecologically dominant and economically important babassu palm (Orbignya phalerata) were studied in northern Brazil. The breeding system of this species is complex. Inflorescences are either morphologically staminate or androgynous. In a functional sense the former are invariably male and the latter generally female, although an intermediate, functionally hermaphroditic type occurs rarely. Individual trees vary from exclusively staminate to predominantly androgynous. In the populations studied, flowering peaked in the rainy season (January-May). Three lines of evidence led us to consider self-pollination extremely rare. First, functionally hermaphroditic inflorescences exhibited protogyny: pistillate flowers were receptive during the first 48 hr following anthesis, and staminate flowers released pollen only thereafter. Second, seed set did not occur in androgynous inflorescences that had been isolated from external pollen sources. Third, simultaneous flowering of staminate and androgynous inflorescences in individual palms was rare. Despite the high abundance and diversity of insects visiting inflorescences, detailed observations indicated that the only likely insect pollinator is the nitidulid beetle Mystrops mexicana. This species occurs in abundance on both flower types and was observed in babassu at sites up to ca 600 km distant, indicating that the association is widespread. Fruit set in inflorescences that had been bagged to exclude insects but not wind-borne pollen indicated that wind pollination also occurs. The latter appears to be more common in such relatively open sites as pastures. The combination of two pollination syndromes clearly enhances this species' adaptability to a wide range of habitats. Evidence from other studies suggests that the combination of entomophily and anemophily may be a recurring phenomenon in palms. HISTORICALLY, PALMS HAVE BEEN CONSIDERED to be primarily wind pollinated (Delpino 1870, Drude 1889, Good 1956) for two reasons. First, palms commonly exhibit many features that are supposedly typical of anemophily, such as small, numerous, dull-colored flowers and abundant, smooth, monosulcate pollen (Schmid 1970b). Second, European botanists were familiar with Phoenix and Chamaerops, both supposedly anemophilous, and almost completely ignorant of tropical palm species in their native environment. Schmid's (1970a, b) work marked a turning point in our understanding. He showed by detailed field work that a small understory palm, Asterogyne martiana, although appearing anemophilous, is in fact entomophilous. Since then many studies have confirmed this mode of pollination in palms. Both Faegri and van der Pijl (1979) and Uhl and Moore (1977) stressed entomophily in palms. Henderson (1986) suggested that most species are entomophilous (and at least in one case, chiropterophilous) and that anemophily is rare. Often two groups of beetles are pollinators and have an intricate association with palm inflorescences, suggesting primitive cantharophily in the family. Many pollination studies, however, are brief and inadequate, and experimental studies are especially lacking. Although entomophily has been assumed, it has rarely been demonstrated. Among the most rigorous studies are those of Sholdt and Mitchell (1967) on Cocos nucifera; Syed (1979) on Elaeis guineensis; and Mora Urpi and Solis (1980), Mora Urpi (1982), and Beach (1984) on Bactris gasipaes. Studies of these cultivated palms indicate that, although entomophily is the predominant mode of pollination, anemophily also occurs. This paper presents the results of a three-year study of the pollination ecology of the babassu palm (Orbignya phalerata Mart.) in northern Brazil. 0. phalerata is the principal species of the babassu complex and ranges from eastern Bolivia through northern and central Brazil to the Guianas. Like many large and poorly collected palms, the taxonomy of this species has generated considerable confusion: frequently cited names such as 0. martiana Barb. Rodr., 0. speciosa (Mart.) Barb. Rodr., and 0. barbosiana Burret have recently been reduced to synonomy under 0. phalerata (Anderson & Balick 1987). A second species of the complex, Orbignya oleifera Burret, appears to be limited to the Sao Francisco River valley in the Brazilian state of Minas Gerais. In addition, both 0. phalerata and 0. oleifera hybridize with other species. A complete review of the taxonomy of this complex has been provided by Anderson and Balick (1987). In the present paper, babassu refers exclusively to 0. phalerata. Babassu attains a maximum height of 35 m and is a common, often dominant element in unaltered tropical dry and moist forests in eastern Bolivia, central and northern Brazil, and the Guianas. On sites where the original I Received 24 June 1986, revision accepted 28 October 1986. 192 BIOTROPICA 20(3): 192-205 1988 This content downloaded from 157.55.39.124 on Wed, 20 Jul 2016 04:45:19 UTC All use subject to http://about.jstor.org/terms vegetation has been cleared, babassu forms pure stands that virtually blanket the landscape, covering an area in Brazil recently estimated at 196,370 km2 (STI 1979). The palm plays an important role in market economies. For example, in 1980 over 250 thousand metric tons of oil-rich kernels obtained primarily from this species were sold to oil-pressing facilities in Brazil (IBGE 1982); the manual extraction of these kernels is a source of livelihood for hundreds of thousands of rural families (May et ail. 1985). In addition to vegetable oil, babassu fruits provide a host of market and subsistence products, including flour, alcohol, charcoal, coke, tar, and combustible gases. In spite of the economic and ecological importance of babassu, its pollination ecology had not been previously studied when we began our fieldwork in 1981. Knowledge concerning babassu's pollination is especially relevant in view of current attempts to domesticate this species (Balick 1984). Recent elucidation of pollination mechanisms in the African oil palm has resulted in greatly increased yields in Southeast Asian plantations (Greathead 1983). In addition to economic considerations, studies of pollination in palms contribute to an understanding of evolutionary trends within the family (Henderson 1986). The most detailed studies to date, however, have focused on cultigens in plantations, where ecological conditions are radically different from those under which these species evolved. This paper attempts to fill the gap by presenting the first long-term, experimental study of pollination of a wild palm in its natural habitat.
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Anderson et al. (1988) studied this question.