The persistence of ripe fleshy fruits in the presence and absence of frugivores

A trade-off between antimicrobial defences and palatability to dispersers may place limits on fruit persistence in nature. The retention times of ripe fruits on 34 wild plant species under natural conditions (unbagged persistence) and when fruits had been bagged with nylon mesh to exclude frugivores (bagged persistence) were compared in Hong Kong, China (22°N). Bagged persistence is a measure of the effectiveness of fruit defence while unbagged persistence is an inverse measure of attractiveness to vertebrate frugivores. Bagged fruits persisted significantly longer than unbagged fruits in 30 species, with half the species tested persisting for more than 2 months. There was a significant positive relationship between the median persistence times of bagged and unbagged fruits, suggesting that species with a high resistance to microbial infection are also less attractive to frugivores. Both bagged and unbagged fruits persisted significantly longer at lower temperatures. There was a significant positive relationship between bagged persistence time and fibre content of the fruit pulp, but no significant relationships between unbagged persistence and the six fruit traits tested (diameter, pulp as a percentage of fruit fresh weight, and lipid, total soluble carbohydrate, nitrogen and fibre as percentages of pulp dry weight). Mechanical damage significantly decreased the bagged persistence time for half of the species. Although some fruits decayed or dried up while attached to the plant, fruits of 53% of the species remained visually attractive until they fell off.     

Floral phenology and compatibility of sawgrass, Cladium jamaicense (Cyperaceae)

Sawgrass, Cladium jamaicense, is the dominant macrophyte in the Florida Everglades. We examined sawgrass flowering phenology and compatibility reactions in ex situ and in situ populations over 2 yr. Sawgrass flowers in May in southern Florida. Flower maturation was relatively synchronous within an inflorescence. Along the entire inflorescence, functionally male flowers emerged initially, followed by stigmas, then anthers of hermaphroditic flowers. Flowers of each sex expanded over 2 d with less than 1 d in between, totaling 6- 7 d for an inflorescence to complete flowering. Hand pollinations showed that sawgrass was self-compatible and not pollen-limited, because open pollinations produced fruit set similar to self- and cross-pollinations. Fruit set was low in autogamy and manipulation treatments. Manipulation treatments were used to study the effect of exposure to airborne pollen during hand pollinations. This treatment thus provides a useful technique for studies on the in situ compatibility of wind-pollinated graminoids. Sawgrass was able to self-fertilize, but the timing of flower maturation on an inflorescence promoted outcrossing. Actual outcrossing rates in sawgrass thus depend on clonal architecture and the timing of floral maturation on other inflorescences within a clone rather than on inflorescences of other genets in a population.     

AMONG- AND WITHIN-FLOWER COMPARISONS OF POLLEN TUBE GROWTH FOLLOWING SELF- AND CROSS-POLLINATIONS IN DIANTHUS CHINENSIS (CARYOPHYLLACEAE)

We compared the rate of pollen tube growth following self- and cross-pollinations both among and within flowers of two clones of Dianthus chinensis L. For among-flower comparisons, both styles of a flower were pollinated with either self- or cross-pollen. Within-flower comparisons were made between the two styles of the same flower, one of which was self-pollinated and the other cross-pollinated. Comparisons between flowers indicated that self-pollen grew slower than cross-pollen in both clones. However, differences in the growth rate of pollen tubes from self- and cross-pollinations were greater when comparisons were made between the two styles of the same flower than when pollinations were made in different flowers. These results suggest the existence of interstyle interactions in pollen tube growth.     

The breeding system of Lycium cestroides: a Solanaceae with ovarian self-incompatibility

To determine the breeding system of Lycium cestroides,several treatments were performed: self-, cross-, and geitonogamous pollinations, autonomous self-pollination, and a control (flowers exposed to natural pollinators). Production and quality of fruits and seeds as well as pollen tube growth were evaluated for each treatment. Experimental pollinations indicate that L. cestroides is self-incompatible since fruits were obtained only under cross-, and open-pollination treatments. However, in self- and geitonogamous hand pollinations, as well as in autonomous self-pollination, pollen tubes developed successfully and reached the ovules. The speed of pollen tube growth did not differ significantly among the different hand-pollinated flowers (cross-, self-, and geitonogamous). These facts indicate the presence of an ovarian self-incompatibility system. Significant differences were observed in fruit set, fruit size, and seed number per fruit between cross-pollinated flowers and open pollination (control). These results could be explained in terms of quantity and quality of pollination in each case. Received: 2 November 2000 / Revision accepted: 26 January 2001     

Density-dependent variation in reproductive success in a terrestrial orchid

 Within population variation in plant density can affect reproductive success and breeding systems. We examined such effects in Listera cordata R. Br., a north temperate terrestrial orchid, in a subalpine population in Colorado, USA. Hand pollinations showed that L. cordata was self-compatible as all pollinations produced fruits. Cross-pollinations differed significantly from self-pollinations, and had a higher number of seeds per capsule and higher % of fertilized ovules. Together they could compensate for the transmission advantage of self-pollinations. Average number of flowers per inflorescence was 4.2–4.4 and average fruit set was 20.7–23.7%. By establishing 36 plots with varying plant densities (1, 4, 8 and 16) and emasculating all flowers in target plants of a set of 20 plots, we estimated density effects on fruit and seed production. Plant density had no effect on the amount of reproduction except in reduced seed production of highly dispersed plants. Our results suggest that inbreeding depression may be an important selective factor in L. cordata. Further studies are needed to define its role in the evolution of mating systems in this species. Received February 21, 2000 Accepted December 26, 2000     

Pollen quality limits seed set in Burchardia umbellata (Colchicaceae)

In self-incompatible plants, interference by self pollen or genetically related pollen can potentially exacerbate pollen limitation, although this has rarely been demonstrated. We examined the breeding system, pollen limitation, and pollen interference using self- and cross- pollinations and pollen supplementations in Burchardia umbellata, an insect-pollinated lilioid monocot. Ovule fertilization and seed set were less following selfing than crossing (22 vs. 78% and 4 vs. 73%, respectively), indicating partial self-incompatibility. Flowers were partially protandrous, and flowers opened concurrently on plants potentially allowing self pollen interference. Natural seed set was pollen limited and varied within and among years, probably due to variation in flowering plant density. Interference by self or genetically related pollen caused pollen limitation as evidenced by increased seed set of bagged cross-pollinated plants compared to unbagged pollen-supplemented plants in two years. In 1996, both fertilization and seed set increased in response to cross-pollination, indicating that interference occurred in the style and ovary. In 1997, only seed set increased after cross-pollination indicating that interference occurred in the ovary. Inappropriate pollen deposition may contribute to pollen limitation more often than previously recognized and should select for floral traits that decrease deposition of self or related pollen.     

COMPETITION-DEPENDENT ABSCISSION OF SELF-POLLINATED FLOWERS OF PHORMIUM TENAX (AGAVACEAE): A SECOND ACTION OF SELF-INCOMPATIBILITY AT THE WHOLE FLOWER LEVEL?

The relative success of fruit from paired self- and cross-pollinations was examined in Phormium tenax when the contrasted pollinations were separated by different distances on the same and different inflorescences. We determined whether the retention of selfed fruits differed from that of crossed fruits and whether it depended on the level of competition with crossed fruit, the number of seeds per fruit, and/or the presence of earlier developing fruit. We found that the success of selfed fruits is determined by the degree of competition with crossed fruits and may be an expression of self-incompatibility. Competition-dependence of the abscission of selfed flowers has not been documented previously. It is parallel to cryptic self-incompatibility in which individual self-pollen grains are not as successful as cross-pollen when competing on the same pistil. The competition-dependent abscission of self-pollinations considered here, however, operates at the level of whole flowers. The phenomenon of competition-dependent abscission of selfed flowers in P. tenax also has implications for the measurement and interpretation of self-incompatibility in other species. Self-incompatibility is a quantitative phenomenon. The facultative success of selfing shows that the effective strength of self-incompatibility can be highly susceptible to the conditions of competition under which it is measured. The competition-dependent abscission of selfed flowers allows a high level of outcrossing to be achieved while it assures seed set when pollinations are scarce. Several other causes of intermediate selfing frequencies can also be explained by this “best-of-both-worlds” hypothesis.     

Effects of self-, chase and mixed self/cross-pollinations on pistil longevity and fruit set in Ceiba species (Bombacaceae) with late-acting self-incompatibility

BACKGROUND AND AIMS: Late-acting self-incompatibility (LSI), in which selfed flowers fail to form fruits despite apparently successful growth of the pollen tubes to the ovules, is a contentious and still poorly understood phenomenon. Some studies have indicated pollen tube-pistil interactions, and major gene control. Others favour an early acting inbreeding depression explanation. METHODS: Experimental pollinations, including selfs (in a subsample of which the style was cut before pollen tubes reached the ovary), chase self/cross-pollinations, crosses, and mixed self/cross-pollinations were used to study floral/pistil longevity and effect on fruit set and seed yield in two Ceiba species known to have LSI. RESULTS: Self-pollinations, including those with a cut style, had extended floral longevity compared with unpollinated flowers. Chase pollinations in which cross-pollen was applied up to 3 h after selfing set fruits, but with reduced seed set compared with crosses. Those with cross-pollen applied at 4 and 8 h after self-pollination all failed to set fruits. Flowers subjected to 1 : 1 and 2 : 1 self/cross-pollinations all produced fruits but again with a significantly lower seed set compared with crosses. CONCLUSIONS: Extended floral longevity initiated with self-pollen tubes growing in the style indicates some kind of pollen tube-pistil interaction. Fruit set only in chase pollinations up to 3 h implies that self-pollen tubes either grow more slowly in the style or penetrate ovules more slowly on arrival at the ovary compared with cross-tubes. This agrees with previous observations indicating that the incidence of penetrated ovules is initially lower in selfed compared with crossed pistils. However, the low seed yield from mixed pollinations indicates that self- and cross-pollen tubes arrive at the ovary and penetrate ovules more or less simultaneously. Possible explanations for these discordant results are discussed.     

Intrapopulation variation in the breeding system ofVillarsia lasiosperma (Menyanthaceae), a distylous species

The restricted perennial diploid herb,Villarsia lasiosperma, of southwestern Western Australia has distylous flowers with dimorphism in style and stamen length, stigma morphology, and pollen size. In order to assess the presence and nature of an incompatibility system in this species, a crossing program was carried out using 17 plants grown from seeds collected in two field populations. Pollen stainabilities of these plants mostly exceeded 95%. Mean seed-set of Longs following intermorph pollinations was c. 24 seeds per pollination and for Shorts was c. 16 seeds per pollination. Approximately three-quarters of the Longs and Shorts produced no seeds after self-pollination; the remainder produced very few seeds following such pollinations. No Shorts produced seeds after intramorph cross-pollinations. However, about half the Longs exhibited various levels of weakened intramorph incompatibility, with mean seed-sets following intramorph cross-pollinations up to half the mean seed-sets following intermorph pollinations. In the behavior of Longs, the incompatibility system ofV. lasiosperma differs from the idealized distylous breeding system, but resembles that of a purported close relative,V. exaltata of eastern and southeastern Australia.     

REPRODUCTIVE PROFICIENCY IN PAEONIA CALIFORNICA (PAEONIACEAE)

Study of three populations of geophytic Paeonia californica in southern California revealed considerable variation, within and between populations, in both potential and in realized seed output. Plants are weakly self-compatible, but natural seed set (x = 4.2 seeds per carpel) is closer to seed set produced in hand cross-pollinations (x = 4.5) than in self pollinations (x = 1.4). Flowers are protogynous, nectariferous, and scented; 17 species of bees in four families, and one species of melyrid beetle were found in them and probably account for pollinations at these sites. Counts of reproductive parts show greatest inter-population variation in mean numbers per plant, of flowers (population means ranged from 16.2 to 21.2), ovules (744 to 1142), pollen grains (23 million to 38 million), and % viable pollen (26.6 to 81.4). Seed set also varied significantly, with only 11.4 to 26.8 % of the ovules maturing into seeds. This low reproductive success is probably correlated with the genetic anomalies studied by others—particularly the translocation heterozygosity that causes lowered production of viable gametes. The relatively few seeds produced are heavy (x = 0.184 g per seed), and germination percentages are high (x = 80%). The elongation of cotyledon bases during hypogeal germination seems to permit optimal germination at soil depths of only 2–3 cm, but environmental factors such as drought stress and herbivore pressure promote high seedling mortality.     

Foliar application of aminoethoxyvinylglycine (AVG) delays fruit ripening and reduces pre-harvest fruit drop and ethylene production of bagged “Kogetsu” apples

Covering apple fruits with double layer waterproof bags to enhance fruit quality and evenness of blush colour is typical on many cultivars in Korea and Japan. Aminoethoxyvinylglycine (AVG) applied to unbagged apple fruits at 3–4 weeks before commercial harvest reduces ethylene production in the fruit, delays fruit ripening and reduces pre-harvest fruit drop. Spray application of AVG to trees of bagged apples should have no effect on apple ripening as there is␣no direct contact with the fruit and the translocation of AVG in apple trees is regarded as negligible. However, preliminary experiments suggested that AVG applied to trees of bagged apples reduced pre-harvest fruit drop in “Kotgetsu” apples. This study investigated the effect of spray treatments of 125 ppm of AVG on fruit drop, fruit ripening (firmness, starch conversion and soluble solids) and ethylene production to whole trees with bagged or unbagged “Kogetsu” fruit, as well as sprays of only the bagged or unbagged fruit on trees on two orchards. AVG applied to whole trees with unbagged apples reduced fruit drop from an average of 58.9% to 10.4%, delayed starch conversion and decreased ethylene production. AVG applied to whole trees with bagged fruit was equally effective in reducing pre-harvest drop, delaying fruit ripening and reducing ethylene production. Application of AVG to unbagged fruit only was nearly as effective as application to whole trees with unbagged fruit but application to bagged fruit only had no effect on fruit ripening or ethylene production. Application of AVG to bagged fruit only did reduce fruit drop to an average of 42.5% but this was not as effective as spraying unbagged fruit only or whole trees with bagged fruit. Possible mechanisms for this effect are discussed.     

Pollination ecology of Penstemon roseus (Plantaginaceae), an endemic perennial shifted toward hummingbird specialization?

Summary Pink-flowered tubular Penstemon roseus (Plantaginaceae), which has shifted partially to hummingbird pollination, blooms on high-elevation slopes in the mountains in Tlaxcala, Mexico. We studied the interactions between pollinator visitation rates to flowers, pollen removal and deposition, flower size, and nectar removal frequency on seed production in P. roseus. We combine observational and experimental studies in two contrasting natural populations. Our manual pollinations revealed that P. roseus is fully self-compatible. Autonomous self- and manual self-pollinated flowers matured as many seeds as when outcrossed, but outcrossing seems to become better than selfing as the flowering season progressed. Early in the season flowers that were bagged and hand-selfed, hand-outcrossed, or autonomously selfed, or unbagged and naturally pollinated had equal seed set in all four treatments. But later in the season, outcross pollen gave approximately twice as much seed set as the two self-treatments. Low levels of pollen receipt and pollen removal were consistent with the long time elapsed for a given plant to be visited by hummingbirds, which suggests pollen shortage in both sites. Despite differences in pollinator visitation rates to flowers, probability of flower visitation, removal and deposition of pollen, and nectar production rates between populations, we found that total nectar production had no effect on seed production at either site. The daily nectar secretion rate of 0.3–0.65 mg sugar per flower per 1–3 days was low relative to other hummingbird-adapted Penstemon species (typical range: 1.5–5 mg sugar per flower), and it might be intermediate between hummingbird- and bee-adapted Penstemon flowers. Our results support the hypothesis about a shift toward hummingbird pollination, and provide an example of a ‘despecialized’ Penstemon species, which attracts high-energy pollinators (hummingbirds) and profits from outcrossing, but retains bee-syndrome floral traits and low sugar production rates.     

Pollen tube growth and self-incompatibility in three Ziziphus species (Rhamnaceae)

Self-incompatibility and synchronous protandrous dichogamy have previously been reported in Ziziphus species. In this work, we conducted a comparative analysis of fluorescence microscopy observations of pollen tube growth following controlled cross pollinations of emasculated flowers and self-pollinations of non-emasculated flowers in three Ziziphus species, Z. jujuba, Z. mauritiana and Z. spina-christi, with the aim to determine the type of the self-incompatibility system of each species. In addition, to test whether autonomous self-pollination, parthenocarpy or agamospermy occurs, flowers were emasculated (or not) and covered. Fruit set and seed viability were monitored. The presence of binucleate pollen grains and the cessation of pollen tube growth in the style suggest that the self-incompatibility system operating in the studied Ziziphus species is gametophytically controlled. Controlled self-pollination in Z. mauritiana resulted in fruits that dropped off before maturation, whereas in Z. spina-christi the flowers dropped off one or two days after pollination. Following controlled self-pollination, small fruits lacking viable seeds were obtained in Z. jujuba, probably due to the stimulus provided by pollination (stimulative parthenocarpy). In the cultivar Tamar of Z. jujuba, the relatively high percentage of seedless fruits obtained in emasculated bagged flowers without hand pollination suggests that this cultivar can set seedless fruits without any pollination stimulus.     

Population differences in self-fertility in the “self-incompatible” milkweed Asclepias exaltata (Asclepiadaceae)

Individual plants of Asclepias exaltata (Asclepiadaceae) typically express an unusual self-incompatibility system under single-gene control. Hand-pollinations performed in six natural populations detected occasional self-fertile plants. The frequency of self-fertile individuals ranged from 0 to 34.0% and differed significantly among populations. Self-fertility appears to be under genetic control, as the ability of most plants (80.0 %) to set fruit following self-pollinations was identical under natural and greenhouse conditions. Seed- and fruit-set, however, were significantly lower from self- vs. cross-pollinations. Allozyme analysis of the population with the highest frequency of self-fertility revealed that adult plants were not significantly inbred. Finally, fruit-set following within-population cross-pollinations did not differ from that following wide, between-population cross-pollinations.     

Pollination and seed production in Xerophyllum tenax (Melanthiaceae) in the Cascade Range of central Oregon

Xerophyllum tenax is a mass-flowering, nectarless herb in which self-pollination is unavoidable as anthers shed pollen onto the three, receptive stigmatic ridges attached to each pistil within a few hours after expansion of the perianth. We compared the pollination system with reproductive success in this species through controlled, hand-pollination experiments. Ovaries of flowers sampled from unbagged inflorescences were visited by pollen-eating flies (primarily members of the family Syrphidae), beetles (primarily Cosmosalia and Epicauta spp.), and small bees, and produced normal-sized capsules and mature seeds. Ovaries of flowers from inflorescences bagged to prevent insect pollination produced small capsules containing undeveloped or no seeds. Epifluorescence analyses suggest that 0.95 of the uncovered flowers are cross-pollinated by insects with pollen tubes penetrating style and ovary tissue. Flowers show a "leaky" but early-acting self-incompatibility system. While hundreds of pollen tubes germinate on each stigmatic surface following self-pollination, few pollen tubes penetrate the stigmatic surface and none penetrate the ovary. In contrast, when stigmas are cross-pollinated by hand with pollen from a second inflorescence pollen tubes were seen penetrating style and ovary. Self-incompatibility in X. tenax parallels that of some species of Trillium, a sister genus within the Melanthiaceae.     

Trimorphic incompatibility in Eichhornia azurea (Pontederiaceae)

Eichhornia azurea (Pontederiaceae) is a mat-forming, clonal aquatic that inhabits lakes, marshes and river systems in many parts of the Neotropics. The species is tristylous with long-, mid-, and short-styled morphs commonly represented in natural populations. To investigate whether E. azurea possesses a trimorphic incompatibility system typical of tristylous species, we conducted a controlled pollination experiment on 15 clones representing the three style morphs from a natural population near Rosario, Argentina. Comparisons of fruit and seed set following self-, illegitimate, and legitimate pollinations clearly demonstrated the presence of trimorphic incompatibility in E. azurea. Self- and illegitimate pollinations produced significantly less fruit and seed than legitimate pollinations in all three style morphs. Pollen from the two anther levels within a flower exhibited contrasting compatibility relations in self-pollinations. In common with several other tristylous species in Pontederiaceae, the expression of self-incompatibility was weakest in the mid-styled morph and strongest in the short-styled morph. We discuss the ecological and evolutionary significance of the partial expression of trimorphic incompatibility in E. azurea. Received: 3 May 1999 / Revision accepted: 27 July 1999     

Nocturnal Versus Diurnal Pollination Success in Isertia laevis (Rubiaceae): A Sphingophilous Plant Visited by Hummingbirds

Abstract: Isertia laevis (Rubiaceae) possesses flowers with traits typical for the pollination syndrome of sphingophily. Diurnal flower observation showed that nine different hummingbirds (Trochilidae) and one flower piercer (Coerebidae) were frequent visitors. Their activity on the flowers peaked in the morning hours. Very low nectar volumes were found in the morning (8.00 h) in unbagged flowers. Nectar volumes, however, reached their peaks (27 μl) at night (2.00 h) in bagged, as well as in unbagged flowers. At night few individuals of sphingids were observed. Pollination experiments showed that flowers presented to nocturnal pollinators from 18.00 h to 6.00 h had low fruit set (14 %) but high seed set (59 %). Flowers accessible from 6.00 h to 18.00 h for diurnal flower visitors showed high fruit set of 63 % but low seed set of 14 %. This suggests that pollination of individual flowers is less effective during daytime. Regarding relative reproductive success, i.e., efficiency of pollination defined as fruit set x seed set, both diurnal and nocturnal pollinators, however, are equally successful. We conclude that frequently occurring, but not very effective pollinators contribute substantially to seed production, when the expected pollinators are scarce.     

Pattern of Flower and Fruit Production in Stryphnodendron adstringens, an Andromonoecious Legume Tree of Central Brazil

Abstract: Patterns of flower and fruit production in racemes of Stryphnodendron adstringens, an andromonoecious Brazilian savanna tree species, were studied in two natural areas near Uberlândia-MG. Racemes were divided in three parts: apex, centre, and base. Number of flowers, gender, and nectar and pollen production were analyzed for each section. Frequency of visitors to each part of the inflorescence was also quantified. Hand self- and cross-pollinations were performed in complete racemes and fruit set used to determine breeding system. The racemes produced a mean of 329 flowers, more densely packed in the central portion. Hermaphrodite and male flowers occur along the inflorescence but hermaphrodite flowers are more common in the centre. Fruit set was markedly low but does not seem to be limited by pollination service, since free open-pollinated racemes and hand cross-pollinated ones do not differ in fruit production rates. Fruits resulted mostly from cross-pollinated flowers and fruit production was biased to the central portion of the raceme. Nectar yield was higher in the central portion of the raceme and visitors arrived more commonly on this portion of the inflorescence. However, most flowers did not produce nectar. The pattern of fruit production seems to be a consequence of the hermaphrodite flower distribution in the raceme and it is not constrained by pollen flow or flower opening sequence.     

Distyly in Linum pubescens and L. mucronatum

In Linum pubescens Banks & Solander and L. mucronatum Bertol. two floral morphs occur, differing in style length, stamen length, size of stigmatic papillae and, in L. mucronatum , exine sculpture of pollen grains. In both species artificial self- and intramorph cross-pollinations were incom, patible. Intermorph pollinations resulted in seed production. The inhibition of pollen-tube growth in incompatible pollinations occurs within the stigma. In L. pubescens distyly seems to be governed by a single pair of alleles. In natural populations the two morphs were found to be represented by approximately equal numbers of individuals. The effectiveness of the complementary arrangement of anthers and stigmas in promoting intermorph pollinations and in preventing pollen wastage in incompatible pollinations is discussed.     

Synchronized protandry and hermaphroditism in a tropical secondary forest tree, Schefflera heptaphylla (Araliaceae)

Selection favoring avoidance of stigma clogging, pollen discounting, self-fertilization, and other negative effects of self-pollination can produce intricate patterns of intra- and interfloral dichogamy in plants bearing numerous flowers. Here we report an extensive study of the relationships among dichogamy, floral sex allocation (pollen-to-ovule ratios), nectar production, floral visitors, mating system, and fruit set in natural populations of Schefflera heptaphylla, a widespread paleotropical secondary forest tree that produces thousands of flowers in a blooming season. Each tree produces 15?C30 sequentially blooming, paniculate, compound inflorescences. Each compound inflorescence has up to three orders of umbellets, which also bloom sequentially. While hand-pollinations showed that S. heptaphylla was capable of self-fertilization, our observations of thousands of flowers showed that strong intra- and interfloral protandry severely restricts both autogamous and geitonogamous self-pollination. All flowers were bisexual, thus the sexual system of the populations we studied was hermaphroditism. The pollen-to-ovule (P/O) ratios were characteristic of outcrossing species, and P/O ratios of flowers in the last-maturing (third order) umbellets were significantly higher than those in earlier-maturing (first and second order) umbellets. Floral visitors were primarily flies (Chrysomya sp. and Syrphinae sp.) and wasps (Vespula sp. and Eumenes sp.). Flowers produced nectar during both the male (pollen presentation) and female (stigma receptivity) stages of their development, and the volume of nectar production was higher in the female stage. Nevertheless, flowers received fewer visits in the female stage than they did in the male stage, and natural fruit set was low, especially in first and third order umbellets. Fruit set from hand cross- and self-pollinations was significantly higher than natural fruit set, indicating pollen limitation of fruit set. Schefflera heptaphylla has also been reported to be andromonoecious. Both hermaphroditism and andromonoecy are consistent with theoretical predictions for variation in sex allocation among sequentially maturing flowers in protandrous species. Further studies comparing hermaphroditic and andromonoecious populations of S. heptaphylla could elucidate the selective factors affecting sex expression, nectar production, and fruit set in species with numerous flowers displaying both intra- and interfloral dichogamy.