Reproductive biology ofCistus ladanifer (Cistaceae)

The phenology, major floral characteristics, fruiting levels, and breeding system ofCistus ladanifer L. (Cistaceae), a common western Mediterranean shrub species, were studied in a southern Spanish population. The white, large (64 mm in diameter) flowers of this shrub appear during spring (March–May) and produce abundant pollen and nectar. In the year of study, flowers lasted up to three days, during which they were visited by a diverse array of insects including beetles, flies, and bees. Hand-pollinations revealed that flowers do not set any seed unless cross pollen is applied to the stigma. Microscopical observations indicate that self pollen tubes grow down the stigma but invariably fail to induce fruit maturation. At the plant level, all estimates of fecundity investigated (number of seeds per capsule, proportion of ovules developing into seed, and proportion of flowers setting fruit) were highly dependent on nearest neighbour distance, with isolated plants setting as little as 0% fruit. In contrast, plants within a clump often transformed into fruit as much as 90% of the flowers. At the population level, seed output was estimated to range between 3,000 and 270,000 seeds per plant during 1991.     

Effects of pollen quality and quantity on pollen limitation in Crataegus monogyna (Rosaceae) in NW Spain

Pollen limitation occurs when plants produce less fruits and/or seeds than they would with adequate pollen receipt. If the addition of cross-pollen to stigmas increases fruit/seed production, it is interpreted as an evidence of pollen limitation. Much of the limitation may be associated with the quality rather than quantity of pollen; however, most studies do not discriminate between the two, which may lead to misinterpretation of the results. We studied the effects of quality and quantity of pollen on the reproduction of a northern Spanish population of Crataegus monogyna. The treatments included self- and cross-pollination, and supplementation to open and bagged flowers. The response variables considered were number of pollen grains per stigma, pollen tubes per style, and initial and final fruit set. In the Cantabrian range, C. monogyna requires insect pollinators to set fruit and is partially self-incompatible. We found that the number of pollen tubes did not differ between cross- and self-pollination treatments; however, self-pollinated flowers set less fruits than flowers that received pure cross-pollen or were supplemented with both cross- and self-pollen. The experimental design allowed us to infer qualitative rather than quantitative pollen limitation. Comparison of the number of pollen grains and tubes, and initial and final fruit set among pollination treatments suggested post-zygotic embryo selection against selfed progeny.     

Microgametophytes in flowers with and without fruits ofPhlox drummondii (Polemoniaceae)

Relationships between microgametophyte numbers per flower and fruit-set were sought inPhlox drummondii Hook. This was accomplished by counting fluorescentstained pollen tubes in flowers with and without fruits in 21 populations, and in flowers subject to either supplemental or sparse pollination, and then determining whether the flowers initiate fruits. There was a conspicuous variation in mean pollen tubes per flower (3–38) and in percent fruit-set (17%–92%) among populations. Neighboring populations often differed strikingly in these respects. Flowers with fruits had an average of 15.2 pollen tubes per stigma whereas those without had an average of 3 7 tubes. Over all flowers, there was a mean of 3.7 tubes per ovule. There was a strong correlation between mean tube number within populations and their percent fruit-set (r = 0.86). Supplemental pollination significantly enhanced fruit-set, thereby supporting the notion that fruit-set was pollen-limited in most populations. In both natural and artificial pollinations a portion of flowers without fruits still had several pollen tubes. The occurrence of fruitless flowers containing tubes is explained by attrition factors, like late-acting pollen-pistil incompatibility, and resource limitation. Fruit-set could be initiated with one pollen tube, but this rarely occurred in nature. Higher pollen loads were accompanied by higher percents of fruit-set and number of seeds per flower.     

Pollination intensity and potential seed set in Passiflora vitifolia

Summary Initial seed set and fruit set were pollen-limited in a Costa Rican population of Passiflora vitifolia, a self-incompatible species with 200–350 ovules per flower. Pollination intensity was measured by counting the number of allogamous pollen grains on stigmas of the large one-day flowers. Hand-pollinations demonstrated that 25–50 pollen grains are required for fruit set, and >450 are needed for maximum seed set, with a pollen:seed ratio of about 1.6:1.0. Hummingbirds (Phaethornis superciliosus) delivered sufficient allogamous pollen for maximum seed set to only 28% of the flowers examined. Naturally pollinated flowers yielded fewer fruits and fewer seeds per fruit than those pollinated by hand. Most pollen transferred by humming-birds was self-incompatible; emasculated flowers yielded higher seed set than flowers with intact anthers. Visitation rates did not provide a good index of effective pollination.There were significant differences in ovule number, maximum seed set, and maximum per cent seed set among individual vines. More than half of an individual's flowers failed to set fruit, whether pollinated by birds or by hand. In this population, maximum reproductive potential may be limited by maternal resources for fruit development, but seed set varies with pollination intensity. Pollen-limited seed set may be a disadvantage of self-incompatibility, especially in species with many-seeded fruits.     

Pollen load size, reproductive success, and progeny kinship of naturally pollinated flowers of the tropical dry forest tree Pachira quinata (Bombacaceae)

Several studies have demonstrated, using controlled pollinations, that the number and identity of pollen grains deposited onto a flower's stigma affect the reproductive success of plants. However, few studies have shown this relationship under conditions of natural pollination. Using the tropical dry forest tree Pachira quinata, we evaluated the relationship between the number of microgametophytes per pistil and the number of sires with respect to the production of fruits and seeds in a natural population of Pachira quinata. Our study demonstrates that fruit and seed production are directly related to the number of microgametophytes per pistil in natural populations of P. quinata. Only 6% of the marked flowers developed into mature fruits and 10% of the marked flowers initiated fruits but later aborted them. A mean of 23 pollen grains were required to produce a seed. Flowers with >400 pollen grains on the stigma always developed into mature fruits, whereas flowers that received <200 grains never matured fruits. Half of the pollen grains transferred to a flower stigma germinated and developed pollen tubes to the base of the style. The number of pollen grains on a stigma explained 34% of the variation in seed number per fruit, and the number of seeds produced per fruit is positively correlated with the size of the seeds. The population of P. quinata studied is predominantly outcrossing, and seeds within fruits are sired by one or a few donors. The total seed crop within trees was sired by three to five donors. Our study examined the implications of the variation in size of microgametophyte loads per pistil with respect to the breeding system and the paternity of progeny under natural conditions. The competitive ability of pollen and pollen tube attrition are important factors regulating fruit production in P. quinata.     

Effects of pollen reward removal on fecundity in a self-incompatible hermaphrodite plant

The pollen of hermaphrodite plants is often utilised by flower-visiting animals. While pollen production has obvious benefits for plant male fitness, its consequences for plant female fitness, especially in self-incompatible hermaphrodite species, are less certain. Pollen production could either enhance seed production though increased pollinator attraction, or reduce it if ovules are discounted by deposition of self pollen, as can occur in species with late-acting self-incompatibility. To test the effects of pollen reward provision on female fitness, we artificially emasculated flowers in two populations of the succulent Aloe maculata (Asphodelaceae), which has a late-acting self-incompatibility system, over the course of its flowering period. Flowers of this species are visited by sunbirds (for nectar) and native bees (for pollen and nectar). We measured floral visitation rates, floral rejection rates, pollen deposition on stigmas and fruit and seed set in both emasculated and non-emasculated plants. We found that flowers of emasculated plants suffered reduced visitation and increased rejection (arrival without visitation) by bees, but not by sunbirds; had fewer pollen grains deposited on stigmas and showed an overall decrease in fruit set and seed set. Rates of seed abortion were, however, greatly reduced in emasculated flowers. This study shows that pollen rewards can be important for seed set, even in self-incompatible plants, which have been assumed to rely on nectar rewards for pollinator attraction. Seed abortion was, however, increased by pollen production, a result that highlights the complexity of selection on pollen production in hermaphrodite flowers.     

Comparison of two cacao (Theobroma cacao L.) clones for the effect of pollination intensity on fruit set and seed content

We compared the influence of pollination intensity (PI) on fruit set and seed number per pod in two cacao (Theobroma cacao L.) clones, IFC5 (Forastero Lower-Amazon Amelonado), which is self-compatible and known to produce a high number of seeds per pod under open pollination, and SCA6 (Forastero Upper-Amazon), which is self-incompatible and known to produce a low number of seeds per pod under open pollination. With both clones, PI had a positive effect on fruit set, with the maximum rate requiring more than 150 pollen grains per pod. One-half of the maximum rate of fruit set was reached with 39 pollen grains per pod for SCA6, and 78 for IFC5. With SCA6, a significant positive effect of PI on seed number per pod was also observed, with maximum seed number requiring more than 200 pollen grains per pod. In contrast, seed numbers with IFC5 were approximately equal over the PI range 100–800 pollen grains per pod. Patterns of seed number per pod were compared after: (1) open insect pollination, (2) low-intensity hand pollination and (3) high-intensity hand pollination. The patterns obtained with IFC5 under open pollination showed a peak of 40–50 seeds per pod, whereas the distribution patterns were more even with SCA6. The pattern of seed number under open pollination was similar to that obtained with high-intensity hand pollination for IFC5, and with low-intensity hand pollination for SCA6. We concluded that the high number of seeds per pod observed with IFC5 under natural insect pollination may be explained by a high number of compatible self-pollen grains on the stigma and by a severe drop of low-pollinated flowers eliminating potential lowfilled fruits. With SCA6, however, the number of compatible pollen grains deposited on the stigma was probably low under open pollination, and the flowers required lower pollen quantities to set fruit, which resulted in a high frequency of low seed numbers per fruit. This difference in the capacity to set low-seeded fruits might be considered as an adaptive trait related to the mode of reproduction.     

Studies on heteromorphic self-incompatibility systems: Physiological aspects of the incompatibility system of Primula obconica

Summary In Primula obconica, a species with a heteromorphic self-incompatibility system, the distinction between compatible and incompatible pollen tubes takes place on the stigma surface in thrum flowers, self tubes growing randomly over the papillar cells. No differences were seen between self and cross tube behaviour on the pin stigma surface, but self tubes were inhibited within the stigmatic tissue with differences in tube length evident after 24 h. The stigma surface bears a proteinaceous pellicle and binds the lectin Concanavalin A. Removal of the stigma removes the incompatibility barrier in mature gynoecia. Bud pollination shows that pollen tubes cannot grow in a normal manner on immature stigmas; the random growth of tubes over the stigma surface resembles that of mature thrum selfs. Fewer compatible tubes reach the style base of young gynoecia and smaller numbers of seeds are set than in mature flowers. Pin and thrum pollen grains germinate and grow in aqueous media, thrum tubes growing longer than pin. The presence of H₃BO₄ and CaCl₂ in the growth medium promotes tube elongation and lengths equivalent to compatible styles can be obtained. The pollen grains have proteinaceous materials in their walls which diffuse out on moistening. Prolonged washing in aqueous media removes these materials but the incompatibility reaction remains unchanged. Thus the incompatibility reaction is between pollen tubes and stigmatic tissue and differs from the homomorphic, sporophytic system where pollen wall proteins elicit the incompatibility response.     

The effects of pollen load size and donor diversity on pollen performance, selective abortion, and progeny vigor in Mirabilis jalapa

The influence of pollen competitive environment on pollen performance (pollen germination, stigmatic penetration, and pollen tube growth rate), the maturation or abortion of initiated fruit, seed size, and seedling vigor was explored by manipulating the size and diversity of stigmatic pollen loads on Mirabilis jalapa. All aspects of pollen performance significantly increased with the number of pollen grains on a stigma or pollen tubes in a style, but was not influenced by the diversity of pollen donors. Plants tended to mature single-ovulate fruits that came from flowers where pollen load size and diversity were greatest and aborted those where these were lowest. No plants from seeds resulting from pollinations with a single pollen grain survived, but other fitness measures were mostly determined by maternal plant. The data suggest that pollen performance is influenced by pollen competitive environment, and both the genetic diversity of the pollen load and number of competing pollen tubes are important determinants of seed/fruit abortion.     

Stigma closure and re-opening in Oroxylum indicum (Bignoniaceae): Causes and consequences

The study of plant responses to touch, particularly the responses of leaves, stems, and roots, has a long history. By contrast, floral responses are relatively unexplored. Stigma closure is common in the Bignoniaceae, but the factors influencing it are not well understood. We investigated factors influencing stigma closure and reopening and its effects on pollen receipt in seven Oroxylum indicum trees near Hat Yai, Thailand. The effects of pressure, conspecific and heterospecific pollen, and pollen load (the amount of pollen deposited) on stigma behavior were examined in 270 flowers (of the total 430 flowers evaluated in the entire study). Pressure alone resulted in faster closure than did conspecific pollination and faster reopening than did heterospecific pollination. Stigmas never reopened after conspecific pollination. Pollen load had no effect on stigma behavior. Stigmas discriminated between conspecific and foreign pollen; they reopened only after pollination with the latter. A manipulative experiment revealed that stigma closure did not affect the number of conspecific pollen grains received. We also counted pollen tubes in styles that were either hand-supplemented with outcross conspecific pollen or open-pollinated. Pollen tube numbers were highest after light pollination (～900 grains), indicating that interference among pollen grains may occur after pollination with very heavy loads (>6000 grains). Possible fitness consequences of these responses are discussed.     

PROTANDRY,INCOMPATIBILITY, AND SECONDARY POLLEN PRESENTATION IN CEPHALANTHUS OCCIDENTALS (RUBIACEAE)

Cephalanthus occidentalis L. is protandrous and presents pollen secondarily on the stigma surface. Because self-pollen is present on the stigma, the degree of selling vs. outcrossing in this species will depend on 1) the phenology of pollen presentation and stigma receptivity; 2) whether the species is self-incompatible; and 3) the rates of self vs. crossed pollen tube growth. This study describes floral morphology and phenology, self-incompatibility, and pollen tube growth rates in self- and crosspollinations of C. occidentalis. Light and scanning electron microscopy were used to study stigma morphology after flower opening, while controlled pollinations tested for incompatibility. Stigmas were unreceptive initially but became receptive by the second day after flower opening. Ninety-two percent of cross-pollinated flowers set fruit, compared to 12% fruit set in self-pollinations. Pollen tubes from selfed and out-crossed pollen initially had similar growth rates. Out-crossed pollen tubes began to grow rapidly ca. 5 hr after pollination of a receptive stigma, whereas selfed pollen tubes ceased growth or grew slowly after this time. Pollen tubes from out-crossed pollen grew the length of the style within 24 hr after pollination, while selfed pollen tubes were inhibited at the stigma-style junction. Our results indicate that C. occidentalis has selfincompatibility, in addition to protandry and secondary pollen presentation. Protandry allows removal of self-pollen from the unreceptive stigma, while self-incompatibility prevents fertilization by unremoved self-pollen.     

The timing and effectiveness of sequential pollinations in Hibiscus moscheutos

In many species with animal-pollinated flowers, pollen arrives on the stigma in pulses and late-arriving pollen may be precluded from fertilizing ovules. When seed set per fruit is not pollen limited, the fate of pollen from later cohorts is affected by the time between pollinator visits, variation in pollen tube growth rates, and the amounts of pollen deposited relative to the availability of stigmatic area and unfertilized ovules. In a natural population of Hibiscus moscheutos, we found that consecutive pollinator visits to individual flowers occurred within 15 min of each other in more than half of our observations. We then conducted hand-pollination experiments using equal doses of early and late pollen bearing unique allozyme markers for paternity analysis (each dose was more than sufficient to result in full seed set). When pollen was applied 15 or 30 min after an earlier pollen load, the proportions of seeds sired by late-arriving pollen were reduced by 13–30% and 21–57%, respecitively. A few pollen-tubes from the late pollen load sired seeds even when a large dose of pollen was applied 1–2 h earlier, suggesting that the performance of pollen grains within each cohort was highly variable. The advantage of arriving early was greater when the first pollen load was applied at 0930 hours as compared with 1130 hours. We found no effect of previous pollination on the growth rates of late-arriving pollen-tubes. Taken together, these results demonstrate that pollen from later visits can compete with pollen from earlier visits, but the success of late-arriving pollen typically declines to very low levels after an interval of about 2 h. Given that surplus pollen often arrives on stigmas by mid-morning, we conclude that male reproductive success is more likely to be affected by the timing of pollen dispersal and pollen-tube competitive ability than by the total amount of pollen that is exported from flowers.     

Studies on flower longevity in Digitalis

Flower lifespan was terminated by corolla abscission 5–6 days after stigma opening in the unpollinated flower. Increased pollen loads produced increased seed set and reduced flower longevity progressively to a minimum of one day after pollination with pure pollen. Weakening of the abscission zone was detectable 8 h after pollination, whilst the pollen tubes were still within the stigmatic zone, suggesting that a stimulus, moving at 4 mm h^–1 minimum, was transmitted through the style and ovary. Soon after pollination removal of the stigma prevented the pollination-induced corolla abscission. Later it was necessary to remove the stigma and upper style, and later still the whole style to delay abscission. The progressive induction of the stigma and style took place at a rate of 1.5 mm h^–1, in advance of the pollen tubes which grew at 0.75 mm h^–1. It was not possible to reproduce the pollination effects by application of indoleacetic acid (IAA) to the stigma or the style.Abbreviation IAA Indoleacetic acid     

COSTS OF SELF-POLLINATION IN A SELF-INCOMPATIBLE PLANT,POLEMONIUM VISCOSUM

Plants of Polemonium viscosum are strongly self-incompatible, yet have floral features that enforce spatial and temporal separation of pollen and stigma presentation. In this study, we address the widely held view that such barriers to selfing are maintained because they reduce interference by self pollen in performance of outcross grains. In the first year of the study we found that 24 hr precedence of self pollen on the stigma (24S), reduced outcross pollen germination by 32%, and seed set by 40% in flowers of P. viscosum. In the second year significant negative effects of self pollen on compatible pollen germination were seen when self pollen was applied four hours before (4S) or immediately prior (S×) to outcross pollen. Surprisingly, however, in the second year of study, seed set was not reduced with as much as 50% inhibition of compatible pollen germination. Results suggest that by interfering with normal functioning of outcross grains, incompatible self pollen can increase pollen limitation in P. viscosum. Reduction in seed production as a result of this phenomenon should select for displacement of pollen presentation from stigma receptivity.     

REPRODUCTIVE COSTS OF SELF-POLLINATION IN IPOMOPSIS AGGREGATA (POLEMONIACEAE): ARE OVULES USURPED?

In common with many cosexual angiosperms, the hummingbird-pollinated montane herb Ipomopsis aggregata (Polemoniaceae) is likely to experience self-pollination. Does this incur a fecundity cost even in such a highly self-sterile (presumably self-incompatible) species? Histological studies showed that self pollen germinates, and its tubes penetrate ovules almost as often as those of outcross pollen. Ovules penetrated by self tubes are especially likely to show milky callose occlusion 24–48 hr after pollination, and several observations suggest an association between occlusion and degeneration. Compared to flowers receiving only outcross pollen, seed set was reduced by 42% on average when self pollen was applied along with outcross, either by hand (in emasculated flowers) or by natural autodeposition (in unemasculated flowers). Reductions were statistically indistinguishable whether self pollen was applied 9 hr before outcross pollen, or at the same time. Unemasculated flowers accumulated substantial self pollen loads, and this autodeposition persisted when flowers were probed to mimic hummingbird visitation. Geitonogamy also is substantial, judging from field estimates of pollen transfer. Thus natural self pollen deposition may be sufficient to “usurp” ovules that otherwise could mature. In this light, late-acting self-rejection in I. aggregata seems decidedly less efficient than an early-acting system that would block pollen germination or tube growth.     

FLORAL BIOLOGY,HUMMINGBIRD POLLINATION AND FRUIT PRODUCTION OF TRUMPET CREEPER (CAMPSIS RADICANS,BIGNONIACEAE)

Trumpet creeper is self-incompatible and bears long, tubular, orange flowers from June to September. Flowering peaks rapidly, then declines and continues at low levels for several weeks. The initial burst of flowering may attract pollinators that return even during subsequent reduced flowering. Most flowers open before noon and nectar production totals 110 μl of 26% sucrose equivalents per flower, an exceptionally high production for a temperate zone plant. Production ceases within 20–30 hr of flower opening, but corollas persist for several days and may serve to attract pollinators. Effective pollination reduces the period of stigma receptivity and speeds closing of stigma lobes. Only 1–9% of flowers produced mature fruits at four sites in Illinois and Missouri. Roughly 400 pollen grains had to be deposited on a receptive stigma to cause fruit development beyond an initial period of high abortion. At two sites, 17% and 89% of stigmas received over 400 pollen grains. Assuming 50% of deposited grains were from the same plant, fruit production at one site was clearly pollinator limited, that at the second site may have been. Ruby-throated Hummingbirds (Archilochus colubris) deposited ten times as much pollen per stigma per visit as honeybees (Apis mellifera) and bumblebees (Bombus spp.). Fruit set was highest where rubythroat visitation was most frequent. Trumpet creeper appears primarily adapted for hummingbird pollination, but can also be adequately pollinated by honeybees and bumblebees. This is one of the first attempts to relate pollen-depositing capabilities of pollinators of any plant to pollen requirements for fruit production. Several characteristics suggest that trumpet creeper may be adapted to pollination at low densities (often called traplining) in its presumed original, woodland, habitat.     

Gibberellic acid impairs fertilization in Clementine mandarin under cross-pollination conditions

We investigated the effect of gibberellic acid (GA₃) in the fertilization of Clementine mandarin cv. ‘Clemenules’ (Citrus clementina Hort. ex Tan.), a parthenocarpic variety that produces seedless fruit due to its self-incompatible nature, but yields seedy fruits when grown under cross-pollination conditions.Experiments were conducted with on-tree ‘Clemenules’ flowers and ‘Fortune’ mandarin pollen (C. clementina Hort. ex Tan. × C. reticulata Blanco), which is sexually compatible with the former. Preanthesis treatment at −2 days after anthesis (−2 DAA) enhanced ovule abortion in both unpollinated and cross-pollinated (at +2 DAA) flowers. In the latter, the number of pollen tubes reaching the ovules was significantly reduced although pollen grains were not treated; thus, fertilization was partially avoided and seed set was reduced. When GA₃ was applied at anthesis (0 DAA) at the time of pollination, ovule abortion was again enhanced, and pollen tube growth was completely arrested; thus, fertilization was prevented and seed set was impeded. When GA₃ was applied 24 h after pollination (+1 DAA in flowers pollinated at anthesis), pollen tube growth was impaired but not arrested and ovule abortion was enhanced; therefore, fertilization was not prevented but impaired.We conclude that, when applied the days around anthesis, GA₃ (10 mg l⁻¹) impairs fertilization by either enhancing ovule abortion or reducing pollen tube growth, in ‘Clemenules’ flowers under cross-pollination conditions. The intensity of the response depends on the physiological flower state at the moment of treatment.     

Dry stigmas,water and self-incompatibility in Brassica

The evolution of dry stigmas has been accompanied by the development — in the pollen — of mechanisms for accessing water from the stigmatic epidermis. Development of self- and cross-pollen on the stigmatic surface has been examined in Brassica oleracea, focusing on the hydration of the grains. Unlike self-compatible (SC) Arabidopsis thaliana, pollen hydration of self-incompatible (SI) Brassica oleracea is preceded by a latent period of between 30–90 min, which is significantly shortened by inhibition of protein synthesis in the stigma. Physiological experiments, some with isolated pollen coatings, indicate that during the latent period signals passing from the pollen to the sigma are responsible for readying the stigmatic surface for penetration and — after self-pollination — activation of the SI system. The changes at the stigma surface include the expansion of the outer layer of the cell wall beneath the grain. This expansion does not occur following self-pollination, when coating-derived signals stimulate a stigmatic response which interrupts hydration and arrests grain development. Cell manipulation studies suggest that self grains are not inhibited metabolically, but are physiologically isolated from the subjacent stigmatic papilla. This focusing of the SI response at the pollen-stigma interface ensures that a single papilla can simultaneously accept cross-pollen and reject self-grains. The evolution of this highly efficient SI system is disussed in the perspective of pathogen-defence mechanisms known also to be located in epidermal cells.     

Reproductive ecology of distylous Palicourea Padifolia (Rubiaceae) in a tropical montane cloud forest. I. Hummingbirds' effectiveness as pollen vectors

The adaptiveness of distyly has been typically investigated in terms of its female function, specifically pollen receipt. However, pollen loads on stigmas can only provide moderate support for Darwin's hypothesis of the promotion of legitimate crosses. To determine the effectiveness of hummingbirds as pollen vectors between floral morphs and the consequences in terms of male (pollen transfer) and female function (pollen receipt) in Palicourea padifolia (Rubiaceae), floral visitors, their foraging modes, and temporal patterns of floral visitation were observed and documented. Differences in pollen and stigma morphology, pollen flow, rates of pollen deposition, and/or stigmatic pollen loads were then evaluated for their contribution toward differences in reproductive output between floral morphs. A pollination experiment with stuffed hummingbirds that varied in bill size was done to evaluate the contribution of bill variation toward differences between floral morphs in pollen receipt and pollen transfer and female reproductive output. Anthers of long-styled flowers contained significantly more and smaller pollen grains than those of short-styled flowers, independently of corolla and anther lengths. The shape and orientation of the stigma lobes differed between morphs and were significantly longer among short-styled flowers. Hummingbird visitation rates did not differ significantly between floral morphs, and foraging movements from focal plants towards neighboring plants were independent of floral morph. Stigmatic pollen loads under field conditions and those after controlled hummingbird visitation, along with rates of pollen accumulation through the day indicated that stigmas of short-styled flowers receive proportionately more legitimate (intermorph) pollen grains than did those of long-styled flowers. However, the species of hummingbird was marginally significant in explaining variation in pollen deposition on stigmas. Lastly, intermorph pollinations of P. padifolia resulted in significant differences in fruit production between floral morphs, independent of pollination treatment and pollinator species; short-styled flowers proportionately developed almost twice the number of fruits developed by long-styled flowers.