Choice of food resource by bees and ants (Hymenoptera: Apoidea,Formicidae) on coconut tree inflorescences (Cocos nucifera,Arecaceae)

Coconut trees are mostly anemophilous; however, because bees and ants forage on coconut tree inflorescences for floral food, entomophilous pollination can also occur. The aim of this study was to determine the food resource preference of bees and ants while they collect pollen, nectar and, for ants, occasionally prey on coconut tree inflorescences, as well as to evaluate their impact on self-pollination. The number of ant visits to first female and then male flowers is significantly higher than that of bees. For Apis mellifera (L.) and Pseudomyrmex gracilis (Fabricius) 14% of the sequences were favorable to direct self-pollination. The probability of visits for all of the sequences was similar for both bees and ants and there was no difference in resource choice. For these reasons, neither can be considered a more effective pollinator of the coconut tree.     

Comparative floral biology of Rhynchospora ciliata (Vahl) Kukenth and R. pubera (Vahl) Boeckeler (Cyperaceae): the role of white involucral bracts in attracting pollinating insects

Although Cyperaceae are considered anemophilous, some species exhibit features that are attractive to pollinators, such as the white UV‐reflecting involucral bracts of Rhynchospora ciliata. But how effective are these conspicuous adaptations? To address this question, we tested the hypothesis that species such as R. ciliata are visited by greater numbers of pollinating insects than similar species with green involucral bracts, such as R. pubera. We compared the floral biology of both species and the number of visits to sympatric populations of each species, associating them with the availability of pollen and the pollination system. We verified that species with white involucral bracts are preferred, because there were more visits to R. ciliata in the first 2 h the flowers were open. The peak visitation in R. pubera was 2 h after the flowers opened, when the pollen of R. ciliata was exhausted. Although the involucral bracts of R. pubera are green, the spikelet scales and anthers are white and reflect ultraviolet light. Overall, flowers of R. pubera exhibit fewer white or reflective surfaces and are probably less conspicuous to a bee than those of R. ciliata. It is possible that R. pubera is a second option for visitors after the first 2 h of anthesis. The two different peaks in visitation minimize interspecific competition for pollinators, suggesting that R. ciliata and R. pubera together could attract more generalist pollinators and, instead of competing, facilitate the pollination of both species. Although R. pubera is autogamous and self‐compatible, both wind and insects are important to its reproductive success.     

Gone with the wind: Negative genetic and progeny fitness consequences of habitat fragmentation in the wind pollinated dioecious tree Brosimum alicastrum

Premise

Habitat fragmentation negatively affects population size and mating patterns that directly affect progeny fitness and genetic diversity; however, little is known about the effects of habitat fragmentation on dioecious, wind pollinated trees. We assessed the effects of habitat fragmentation on population sex ratios, genetic diversity, gene flow, mating patterns, and early progeny vigor in the tropical dioecious tree, Brosimum alicastrum.

Methods

We conducted our study in three continuous and three fragmented forest sites in a Mexican tropical dry forest. We used eight microsatellite loci to characterize the genetic diversity, gene flow via pollen distances, and mean relatedness of progeny. We compared early progeny vigor parameters of seedlings growing under greenhouse conditions.

Results

Sex ratios did not deviate from 1:1 between habitat conditions except for one population in a fragmented habitat, which was female biased. The genetic diversity of adult trees and their offspring was similar in both habitat conditions. Pollen gene flow distances were similar across habitat types; however, paternity correlations were greater in fragmented than in continuous habitats. Germination rates did not differ between habitat conditions; however, progeny from fragmented habitats produced fewer leaves and had a lower foliar area, total height, and total dry biomass than progeny from continuous habitats.

Conclusions

Changes in mating patterns because of habitat fragmentation have negative effects on early progeny vigor. We conclude that negative habitat fragmentation effects on mating patterns and early progeny vigor may be a serious threat to the long-term persistence of tropical dioecious trees.

     

Floral scent chemistry and pollination ecology in phytelephantoid palms (Arecaceae)

The subfamilyPhytelephantoideae comprises three genera (Ammandra, Aphandra, andPhytelephas) and seven species of dioecious palms. The floral scents ofAmmandra dasyneura, A. decasperma, Aphandra natalia, Phytelephas aequatorialis, P. macrocarpa, andP. seemannii were analyzed by gas chromatography-mass spectrometry. We studied the pollination biology ofA. natalia, P. aequatorialis, andP. macrocarpa, and tested how the synthetically produced main constituents of the floral scents ofAphandra andPhytelephas attracted insects in two natural populations ofPhytelephas. The genera are distinct in terms of floral scents.Ammandra has sesquiterpenes,Aphandra (+)-2-methoxy-3-sec-butylpyrazine, andPhytelephas p-methyl anisol. These constituents dominated the scents quantitatively and qualitatively. The similarity between scents of male and female inflorescences was 76.5% inAmmandra, 84.2% inAphandra, and >99% inPhytelephas. Different species ofAleocharinae (Staphylinidae) pollinateAphandra natalia andPhytelephas species and reproduce in their male inflorescences.Derelomini (Curculinoidae) andMystrops (Nitidulidae) only visit and pollinatePhytelephas in which male inflorescences they reproduce. A species ofBaridinae (Curculionidae) only visits and pollinatesAphandra natalia, and reproduces in its female inflorescence. The apparent reliance on one or a few floral scent constituents as attractants and few and specific pollinators may indicate co-evolution. Sympatric species ofPhytelephantoideae have different scents. We suggest that species with similar scents have allopatric distributions due to the absence of a pollinator isolation mechanism.     

Moonlight pollination in the gymnosperm Ephedra (Gnetales)

Most gymnosperms are wind-pollinated, but some are insect-pollinated, and in Ephedra (Gnetales), both wind pollination and insect pollination occur. Little is, however, known about mechanisms and evolution of pollination syndromes in gymnosperms. Based on four seasons of field studies, we show an unexpected correlation between pollination and the phases of the moon in one of our studied species, Ephedra foeminea. It is pollinated by dipterans and lepidopterans, most of them nocturnal, and its pollination coincides with the full moon of July. This may be adaptive in two ways. Many nocturnal insects navigate using the moon. Further, the spectacular reflection of the full-moonlight in the pollination drops is the only apparent means of nocturnal attraction of insects in these plants. In the sympatric but wind-pollinated Ephedra distachya, pollination is not correlated to the full moon but occurs at approximately the same dates every year. The lunar correlation has probably been lost in most species of Ephedra subsequent an evolutionary shift to wind pollination in the clade. When the services of insects are no longer needed for successful pollination, the adaptive value of correlating pollination with the full moon is lost, and conceivably also the trait.     

Insect-induced wind pollination of the palm Chamaedorea pinnatifrons and pollination in the related Wendlandiella sp.

In Peruvian Amazonia pollination ecology of two palms, Chamaedorea pinnatifrons (Jacq.) Oerst. and Wendlandiella sp. was studied from October 1988 to January 1990. Both palms are dioecious understory species that form locally dense populations.In C. pinnatifrons both sexes flower synchronously during the dry season. Prior to anthesis, the pendulous male inflorescence is inhabited by numerous thrips (Thysanoptera) and Ptiliidae (Coleoptera). Staminate flowers open by a small basal slit between the petals. At anthesis pollen is shed and the movements of the insects inside the flowers trigger pollen release in small clouds. Thus, the powdery pollen becomes airborne and finally air currents act as a vector, carrying pollen to the inconspicuous female plants, which usually are not visited by insects. The term insect induced wind pollination is suggested for this pollination mode. Wendlandiella flowers during four months in the dry season. Male and female plants were not visited by insects. The dry condition of the pollen indicates that anemophily is the pollination mode in Wendlandiella. Fructification is rare but the plants show intense vegetative propagation.The significance of anemophily in the tropical lowland rain forest is discussed.     

From near extinction to diversification by means of a shift in pollination mechanism in the gymnosperm relict Ephedra (Ephedraceae,Gnetales)

Pollination in gymnosperms is usually accomplished by means of wind, but some groups are insect‐pollinated. We show that wind and insect pollination occur in the morphologically uniform genus Ephedra (Gnetales). Based on field experiments over several years, we demonstrate distinct differences between two Ephedra species that grow in sympatry in Greece in pollen dispersal and clump formation, insect visitations and embryo formation when insects are denied access to cones. Ephedra distachya, nested in the core clade of Ephedra, is anemophilous, which is probably the prevailing state in Ephedra. Ephedra foeminea, sister to the remaining species of the genus, is entomophilous and pollinated by a range of diurnal and nocturnal insects. The generalist entomophilous system of E. foeminea, with distinct but infrequent insect visitations, is in many respects similar to that reported for Gnetum and Welwitschia and appears ancestral in Gnetales. The Ephedra lineage is well documented already from the Early Cretaceous, but the diversity declined dramatically during the Late Cretaceous, possibly to near extinction around the Cretaceous–Palaeogene boundary. The clade imbalance between insect‐ and wind‐pollinated lineages is larger than expected by chance and the shift in pollination mode may explain why Ephedra escaped extinction and began to diversify again.     

Pathways of karyological differentiation in palms (Arecaceae)

Karyological data are given for 56 palm taxa coming from all 6 palm subfamilies. In 11 genera and 17 species, chromosome numbers are reported for the first time. Most chromosome numbers in palms range between 2n = 36 and 2n = 26 in dysploid series. Species of the same genus usually exhibit identical chromosome numbers which additionally may be constant in larger groups of closely related genera (Coryphoideae trib.Corypheae with nearly always 2n = 36,Arecoideae subtribesEuterpeinae andRoystoneinae with 2n = 36,Arecoideae subtrib.Butiinae with mostly 2n = 32). Polyploidy among palms is of minor significance but the endemic Madagascan genusVoanioala (2n = 606 ± 3) is the most striking exception. — With respect to structure of interphase nuclei and longitudinal differentiation of prophase and metaphase chromosomes, the palm family is highly differentiated. Euchromatin types with different prophase condensation properties and fluorochrome and C-banding patterns of heterochromatin permit a discrimination of several subfamilies on the nuclear level (Arecoideae, Ceroxyloideae, Nypoideae, Phytelephantoideae, Calamoideae).Arecoideae andCeroxyloideae, andNypoideae andPhytelephantoideae have some features in common. Subfam.Coryphoideae s. l. is a non-uniform group. — Nuclear characters among palms exclusively found in recentCoryphoideae subtrib.Thrinacinae link palms with other monocotyledons. Most probably, such a nuclear condition represents an ancestral state in the evolution of palm genomes within subfam.Coryphoideae s. l., but also the conspicuous nuclear characters of the other modern palm subfamilies appear to be derived from a similar starting point, since transitional character states are still present in subfam.Calamoideae and some taxa of subfam.Arecoideae. Early karyoevolution in palms obviously did not involve numerical change of the ancient chromosome number of 2n = 36 which started subsequently, as a dysploid reduction in numerous parallel series, independent in subfam.Coryphoideae (2n = 36 to 2n = 28),Calamoideae (2n = 36 to 2n = 26),Ceroxyloideae (2n = 34 to 2n = 26), andArecoideae (2n = 36 to 2n = 28). Possible mechanisms of karyological change are discussed. — Karyological characters are compared to morphological, ecological, taxonomical, and chorological features, and give some new insight into older and more recent phases of palm evolution. (1) Strong deviations in vegetative or floral morphology are often accompanied by major karyological differences, and sometimes the direction of advancement can be traced through intermediate stages. (2) Apart fromCoryphoideae subtrib.Thrinacinae, the strongest concentration of apparently original karyological traits is found in the more basal members of each subfamily. (3) The most successful and actively radiating colonizers of the forest floors in evergreen tropical forests which belong to completely different subfamilies (Old WorldLicuala, New WorldChamaedorea andGeonoma), appear to be very advanced karyologically.     

Phylogenetic relationships of functionally dioecious FICUS (Moraceae) based on ribosomal DNA sequences and morphology

Figs (Ficus, Moraceae) are either monoecious or gynodioecious depending on the arrangement of unisexual florets within the specialized inflorescence or syconium. The gynodioecious species are functionally dioecious due to the impact of pollinating fig wasps (Hymenoptera: Agaonidae) on the maturation of fig seeds. The evolutionary relationships of functionally dioecious figs (Ficus subg. Ficus) were examined through phylogenetic analyses based on the internal transcribed spacer (ITS) region of nuclear ribosomal DNA and morphology. Forty-six species representing each monoecious subgenus and each section of functionally dioecious subg. Ficus were included in parsimony analyses based on 180 molecular characters and 61 morphological characters that were potentially informative. Separate and combined analyses of molecular and morphological data sets suggested that functionally dioecious figs are not monophyletic and that monoecious subg. Sycomorus is derived within a dioecious clade. The combined analysis indicated one or two origins of functional dioecy in the genus and at least two reversals to monoecy within a functionally dioecious lineage. The exclusion of breeding system and related characters from the analysis also indicated two shifts from monoecy to functional dioecy and two reversals. The associations of pollinating fig wasps were congruent with host fig phylogeny and further supported a revised classification of Ficus.     

Phylogenetic relationships among arecoid palms (Arecaceae: Arecoideae)

Background and Aims

The Arecoideae is the largest and most diverse of the five subfamilies of palms (Arecaceae/Palmae), containing >50 % of the species in the family. Despite its importance, phylogenetic relationships among Arecoideae are poorly understood. Here the most densely sampled phylogenetic analysis of Arecoideae available to date is presented. The results are used to test the current classification of the subfamily and to identify priority areas for future research.

Methods

DNA sequence data for the low-copy nuclear genes PRK and RPB2 were collected from 190 palm species, covering 103 (96 %) genera of Arecoideae. The data were analysed using the parsimony ratchet, maximum likelihood, and both likelihood and parsimony bootstrapping.

Key Results and Conclusions

Despite the recovery of paralogues and pseudogenes in a small number of taxa, PRK and RPB2 were both highly informative, producing well-resolved phylogenetic trees with many nodes well supported by bootstrap analyses. Simultaneous analyses of the combined data sets provided additional resolution and support. Two areas of incongruence between PRK and RPB2 were strongly supported by the bootstrap relating to the placement of tribes Chamaedoreeae, Iriarteeae and Reinhardtieae; the causes of this incongruence remain uncertain. The current classification within Arecoideae was strongly supported by the present data. Of the 14 tribes and 14 sub-tribes in the classification, only five sub-tribes from tribe Areceae (Basseliniinae, Linospadicinae, Oncospermatinae, Rhopalostylidinae and Verschaffeltiinae) failed to receive support. Three major higher level clades were strongly supported: (1) the RRC clade (Roystoneeae, Reinhardtieae and Cocoseae), (2) the POS clade (Podococceae, Oranieae and Sclerospermeae) and (3) the core arecoid clade (Areceae, Euterpeae, Geonomateae, Leopoldinieae, Manicarieae and Pelagodoxeae). However, new data sources are required to elucidate ambiguities that remain in phylogenetic relationships among and within the major groups of Arecoideae, as well as within the Areceae, the largest tribe in the palm family.     

Floral trait evolution associated with shifts between insect and wind pollination in the dioecious genus Leucadendron (Proteaceae)

Transitions between animal and wind pollination have occurred in many lineages and have been linked to various floral modifications, but these have seldom been assessed in a phylogenetic framework. In the dioecious genus Leucadendron (Proteaceae), transitions from insect to wind pollination have occurred at least four times. Using analyses that controlled for relatedness among Leucadendron species, we investigated how these transitions shaped the evolution of floral structural and signaling traits, including the degree of sexual dimorphism in these traits. Pollen grains of wind‐pollinated species were found to be smaller, more numerous, and dispersed more efficiently in wind than were those of insect‐pollinated species. Wind‐pollinated species also exhibited a reduction in spectral contrast between showy subtending leaves and background foliage, reduced volatile emissions, and a greater degree of sexual dimorphism in color and scent. Uniovulate flowers and inflorescence condensation are conserved ancestral features in Leucadendron and likely served as exaptations in shifts to wind pollination. These results offer insights into the key modifications of male and female floral traits involved in transitions between insect and wind pollination.     

Mixed mating strategies and pollination by insects and wind in coconut palm (Cocos nucifera L. (Arecaceae)): importance in production and selection

Abstract 1 Coconut is one of the most important tropical crops. It is threatened by Lethal yellowing disease. Production and selection by breeding require pollination, yet little is known of the pollination requirements and breeding system of this palm. 2 This study was carried out from 1999 to 2001 in coconut plantations represented by five coconut ecotypes commonly found in Mexico. It is the first study in the Neotropics on pollination and the breeding system of this palm. 3 Hymenoptera were the most numerous and diverse visitors to coconut flowers. The greatest period of insect abundance occurred during the rainy season (July to October). Insect abundance on the flowers correlated highly and positively with precipitation. 4 The abundance of visitors to pistillate flowers did not vary with season but there were significant differences between palm ecotypes; the most insect‐visited flowers were of the Atlantic Tall ecotype. 5 The introduced honeybee (Apis mellifera) had the most appropriate foraging behaviour, visiting both pistillate and staminate flowers. These insects were probably the most efficient pollinators as they carry pollen on their ventral surface. Ants were present on flowers day and night but had no effect on pollination. 6 Pollination experiments indicated a mixed mating strategy: self‐pollination by geitenogamy produced almost 19% of the fruit set, but cross‐pollination (xenogamy) was the most important contribution (c. 30%). Anemophilous cross‐pollination only accounted for 10% of fruit set, whereas entomophily became the most important pollination mechanism under Yucatan conditions. 7 As coconut palm grows naturally on the oceanic strand in a wide variety of seasonal conditions of wind and rain, we suggest that they may have evolved pollination, breeding and mating systems that ensure fruit production under a wide variety of conditions, while maximizing the probability of cross‐pollination.     

Neither Biased Sex Ratio nor Spatial Segregation of the Sexes in the Subtropical Dioecious Tree Eurycorymbus cavaleriei (Sapindaceae)

Knowledge of sex ratio and spatial distribution of males and females of dioecious species is both of evolutionary interest and of crucial importance for biological conservation. Eurycorymbus cavaleriei, the only species in the genus Eurycorymbus (Saplndaceae), is a dioecious tree endemic to subtropical montane forest in South China. Sex ratios were investigated in 15 natural populations for the two defined ages (young and old). Spatial distribution of males and females was further studied in six large populations occurring in different habitats (fragmented and continuous). The study revealed a slight trend of malebiased sex ratio in both ages of E. cavaleriei, but sex ratio of most populations (13 out of 15) did not display statistically significant deviation from equality. All of the four significantly male-biased populations in the young class shifted to equality or even female-biased. The Ripley's K analysis of the distribution of males with respect to females suggested that individuals of the opposite sexes were more randomly distributed rather than spatially structured. These results suggest that the male-biased sex ratio in E. cavaleriei may result from the precocity of males and habitat heterogeneity. The sex ratio and the sex spatial distribution pattern are unlikely to constitute a serious threat to the survival of the species.     

Non-axillary branching in the palms Eugeissona and Oncosperma (Arecaceae)

FISHER, J. B., GOH, C. J. & RAO, A. N., 1989. Non-axillary branching in the palms Eugeissona and Oncosperma (Arecaceae). The south-east Asian palms, Eugeissona (Calamoideae) and Oncosperma (Arecoideae) are multiple-stemmed. The morphology and development of branching in two species of each genus were examined in Singapore, Borneo, and the Malay Peninsula. Cultivated seedling and adult plants of 0. tigillarium were also observed in Florida. A new shoot arises most often from a longitudinal abaxial groove at the base of an enclosing leaf sheath. In some instances, especially in E. tristis , the enclosing leaf has two equal, adjacent grooves such that any distinction between an original mother shoot and a lateral daughter shoot is impossible. No axillary buds occur in Eugeissona which is hapaxanthic. In Oncosperma , which is pleonanthic, axillary buds are absent from young pre-flowering stems, but an inflorescence bud occurs in the axil of each leaf in older aerial stems. Early ontogenetic stages of vegetative branching, as seen in sectioned apices, indicate that a new vegetative shoot is present on the abaxial base of the first (youngest) leaf primordium. There is no ontogenetic evidence for the displacement of an originally axillary meristem as previously described for the palm Salacca (Calamoideae). Shoot development in Eugeissona is interpreted as a putative dichotomy of the apical meristem in which the meristem centres commonly develop unequally. In Oncosperma the smaller sucker bud meristem may be described as an abaxial leaf base bud, but ontogenetic variations indicate this form of branching is close to dichotomous branching. These new examples of non-axillary branching are compared to similar cases previously reported for palms and other monocotyledons.     

Stamens are not essential as an attractant for pollinators in females of cryptically dioecious Thalictrum pubescens Pursch. (Ranunculaceae)

 It has been hypothesized that females of some dioecious species maintain stamens that produce sterile pollen as a means of attracting pollinators to promote greater seed set. However, this hypothesis has rarely been tested. This paper examines the role of pollinators in the maintenance of sterile stamens in the cryptically dioecious species, Thalictrum pubescens. Wind was found to contribute to pollination; branches of female T. pubescens enclosed in cheesecloth to exclude insects but not wind were still able to set seed. Therefore, females may not need the stamens for pollination. In 1994, insects were found to discriminate against emasculated female flowers, but this discrimination did not lead to a significant difference in either the amount of pollen received or seed set. In 1995, emasculation was combined with the addition of pollen to determine if emasculated females were pollen limited. No significant effect of pollen addition or emasculation was found. Emasculated branches in the pollen-addition treatment appeared to have slightly lower seed set than non-emasculated branches that received pollen, indicating that the slight reduction in seed set was caused by emasculation rather than pollen limitation. Since stamens do not appear to be maintained as pollinator attractants, other explanations, such as genetic constraints, must be investigated. Received: 4 February 1997 / Revision accepted: 20 May 1997     

Reproductive biology and pollination ecology of Triplaris gardneriana (Polygonaceae): a case of ambophily in the Brazilian Chaco

• Triplaris gardneriana (Polygonaceae) is a dioecious pioneer tree reported as insect‐pollinated, despite possessing traits related to anemophily. Here, we analyse the possible roles of insects and wind on the pollination of this species to establish whether the species is ambophilous.
• We carried out observations of floral biology, as well as on the frequency and behaviour of pollinators visiting flowers in a population of T. gardneriana in the Chaco vegetation of Brazil. We conducted experimental pollinations to determine the maternal fertility of female plants and whether they were pollen‐limited, and we also conducted aerobiological experiments to provide evidence of how environmental factors influence atmospheric pollen dispersal.
• The population comprised an area of approximately 152.000 m² and was composed of 603 female and 426 male plants (sex ratio = 0.59:0.41). We observed 48 species of insects visiting flowers of T. gardneriana, of which the bees Scaptotrigona depilis and Apis mellifera scutellata were the most effective pollinators. We recorded pollen grains dispersed by wind on 74% of the glass slides placed on females, located at different distances (1–10 m) from male plants.
• Airborne pollen concentration was negatively correlated with relative humidity and positively correlated with temperature. Our observations and experimental results provide the first evidence that T. gardneriana is an ambophilous species, with pollen dispersal resulting from both animal and wind pollination. This mixed pollination strategy may be adaptive in T. gardneriana providing reproductive assurance during colonisation of sites with different biotic and abiotic conditions.

     

Twenty-five years of progress in understanding pollination mechanisms in palms (Arecaceae)

BACKGROUND: With more than 90 published studies of pollination mechanisms, the palm family is one of the better studied tropical families of angiosperms. Understanding palm-pollinator interactions has implications for tropical silviculture, agroforestry and horticulture, as well as for our understanding of palm evolution and diversification. We review the rich literature on pollination mechanisms in palms that has appeared since the last review of palm pollination studies was published 25 years ago. SCOPE AND CONCLUSIONS: Visitors to palm inflorescences are attracted by rewards such as food, shelter and oviposition sites. The interaction between the palm and its visiting fauna represents a trade-off between the services provided by the potential pollinators and the antagonistic activities of other insect visitors. Evidence suggests that beetles constitute the most important group of pollinators in palms, followed by bees and flies. Occasional pollinators include mammals (e.g. bats and marsupials) and even crabs. Comparative studies of palm-pollinator interactions in closely related palm species document transitions in floral morphology, phenology and anatomy correlated with shifts in pollination vectors. Synecological studies show that asynchronous flowering and partitioning of pollinator guilds may be important regulators of gene flow between closely related sympatric taxa and potential drivers of speciation processes. Studies of larger plant-pollinator networks point out the importance of competition for pollinators between palms and other flowering plants and document how the insect communities in tropical forest canopies probably influence the reproductive success of palms. However, published studies have a strong geographical bias towards the South American region and a taxonomic bias towards the tribe Cocoseae. Future studies should try to correct this imbalance to provide a more representative picture of pollination mechanisms and their evolutionary implications across the entire family.     

Pistillate and staminate flower development in dioecious Pistacia vera (Anacardiaceae)

The development of staminate and pistillate flowers in the dioecious tree species Pistacia vera L. (Anacardiaceae) was studied by scanning electron microscopy with the objective of determining organogenetic patterns and phenology of floral differentiation. Flower primordia are initiated similarly in trees of both sexes. Stamen and carpel primordia are initiated in both male and female flowers, and the phenology of organ initiation is essentially identical for flowers of both sexes. Vestigial stamen primordia arise at the flanks of pistillate flower apices at the same time functional stamens are initiated in the staminate flowers. Similarly, a vestigial carpel is initiated in staminate flowers at the same time the primary, functional carpel is initiated in pistillate flower primordia. Differences between the two sexes become apparent early in development as, in both cases, development of organs of the opposite sex becomes arrested at the primordial stage. Male flowers produce between four and six mature functional stamens and female flowers produce a gynoecium with one functional and two sterile carpels.