Floral Attractiveness Research Articles

Variation in floral morphology, histochemistry, and floral visitors of three sympatric morning glory species.

Three morning glory species in the genus Argyreia Lour., A. lycioides (Choisy) Traiperm & Rattanakrajang, A. mekongensis Gagnep & Courchet, and A. versicolor (Kerr) Staples & Traiperm, were found co-occurring and co-flowering. Argyreia mekongensis and A. versicolor are rare, while A. lycioides is near threatened and distributed throughout Myanmar and Thailand. We investigated key floral characters (floral morphology and phenology, as well as the micromorphology of the floral nectary disc and staminal trichomes) and screened for important chemical compounds hypothesized to contribute to pollinator attraction. Our findings demonstrate that some aspects of floral morphology (e.g., corolla size, limb presence, and floral color) of the three studied congeners exhibit significant differences. Moreover, pollinator composition appears to be influenced by floral shape and size; morning glory species with wider corolla tubes were pollinated by larger bees. The morphology of the floral nectary disc was similar in all species, while variation in staminal trichomes was observed across species. Glandular trichomes were found in all three species, while non-glandular trichomes were found only in A. versicolor. Histochemical results revealed different compounds in the floral nectary and staminal trichomes of each species, which may contribute to both floral attraction and defense. These findings demonstrate some segregation of floral visitors among sympatric co-flowering morning glory species, which appears to be influenced by the macro- and micromorphology of flowers and their chemical compounds. Moreover, understanding the floral morphology and chemical attractants of these sympatric co-flowering Argyreia species may help to maintain their common pollinators in order to conserve these rare and endangered species, especially A. versicolor.

Nitrogen-fixing bacteria boost floral attractiveness in a tropical legume species during nutrient limitation.

Legumes establish mutualistic interactions with pollinators and nitrogen (N)-fixing bacteria that are critical for plant reproduction and ecosystem functioning. However, we know little about how N-fixing bacteria and soil nutrient availability affect plant attractiveness to pollinators. In a two-factorial greenhouse experiment to assess the impact of N-fixing bacteria and soil types on floral traits and attractiveness to pollinators in Chamaecrista latistipula (Fabaceae), plants were inoculated with N-fixing bacteria (NF+) or not (NF-) and grown in N-rich organic soil (+N organic soil) or N-poor sand soil (-N sand soil). We counted buds and flowers and measured plant size during the experiment. We also measured leaf, petal, and anther reflectance with a spectrophotometer and analyzed reflectance curves. Using the bee hexagon model, we estimated chromatic contrasts, a crucial visual cues for attracting bees that are nearby and more distant. NF+ plants in -N sand soil had a high floral display and color contrasts. On the other hand, NF- plants and/or plants in +N organic soil had severely reduced floral display and color contrasts, decreasing floral attractiveness to bee pollinators. Our findings indicate that the N-fixing bacteria positively impact pollination, particularly when nutrients are limited. This study provides insights into the dynamics of plant-pollinator interactions and underscores the significant influence of root symbionts on key floral traits within tropical ecosystems. These results contribute to understanding the mechanisms governing mutualisms and their consequences for plant fitness and ecological dynamics.

Phenotyping floral attractiveness to pollinators using volatilomics, 3D imaging, and insect monitoring

Phenotyping floral attractiveness to pollinators using volatilomics, 3D imaging, and insect monitoring

Floral attractants and rewards to pollinators in Mangifera indica L.

Floral attractants and rewards are essential in plant-pollinator interaction, pollen transfer to and from the flowers, and hence in crop production. In this trial, we determined the attractants and rewards of mango ‘Osteen’ cultivated under a plastic greenhouse. The attractants analyzed were inflorescence architecture and compactness, flower number, size and color patterns. Rewards determined were pollen quantity and its nutritious value and nectar volume and composition. The results show that mango forms panicles with more staminate than hermaphrodite flowers, but the latter are of higher size, more exposed to pollinator activity, and preferentially located in a better-nurtured position within the inflorescence. Pollen produced by staminate and hermaphrodite flowers was similar in quantity and quality. On the contrary, hermaphrodite flowers produced more nectar, likely because of the larger size of their nectary disks. Pollen and nectar present 17 and 22 metabolites, respectively, including carbohydrates, amino acids, and organic acids. Our study provides, for the first time, solid information about the floral attractiveness and rewards of mango cultivated under plastic greenhouses. This will help to understand the possible adaptations required for pollinating this crop under protected cultivation.

Transcriptome-wide analysis of PIP reductase gene family identified a phenylpropene synthase crucial for the biosynthesis of dibenzocyclooctadiene lignans in Schisandra chinensis

Phenylpropenes, such as isoeugenol and eugenol, are produced as defend compounds, floral attractants, and flavor constituents by phenylpropene synthases belonging to the PIP reductase family. Moreover, isoeugenol is proposed to be involved in the biosynthesis of dibenzocyclooctadiene lignans, the main active compounds of Schisandra chinensis (Turcz.) Baill. fruits (SCF). S. chinensis, a woody vine plant, is widely used for its medicinal, horticultural, edible, and economic values. In this study, nine ScPIP genes were identified and characterized from the transcriptome datasets of SCF. The expression profiles revealed that ScPIP genes were differentially expressed during different developmental stages of SCF. Three ScPIPs were selected and cloned as candidate genes encoding phenylpropene synthases according to phylogenetic analysis. ScPIP1 was proved to function as isoeugenol synthase (IGS) and designated as ScIGS1 through in vivo functional characterization in Escherichia coli. Subcellular localization analysis demonstrated that ScIGS1 was localized in both the cytoplasm and nucleus. The three-dimensional (3D) model of ScIGS1 was obtained using homology modeling. Site-directed mutagenesis experiments revealed that the substitution of residues at positions 110 and 113 impacted the product specificity of ScIGS1 and the mutation of Lys157 to Ala abolishing catalytic function. Moreover, the kcat values of mutants were lower than that of ScIGS1 using a deep learning approach. In conclusion, this study provides a basis for further research on PIP reductases and the biosynthetic pathway of dibenzocyclooctadiene lignans.

Floral attractants in an alpine environment: linking floral volatiles, flower size and pollinators

Floral attractants in an alpine environment: linking floral volatiles, flower size and pollinators

The interplay between scale, pollination niche and floral attractiveness on density-dependent plant-pollinator interactions.

Pollinators mediate interspecific and intraspecific plant-plant indirect interactions (competition vs. facilitation) via density-dependent processes, potentially shaping the dynamics of plant communities. However, it is still unclear which ecological drivers regulate density-dependent patterns, including scale, pollination niches (i.e., the main pollinator functional group) and floral attractiveness to pollinators. In this study, we conducted three-year field observations in Hengduan Mountains of southwest China. By gathering data for more than 100 animal-pollinated plant species, we quantified the effect (positive vs. negative) of conspecific and heterospecific flower density on pollination at two scales: plot-level (4m2) and site-level (100-5000m2). Then, we investigated how pollination niches and floral attractiveness to pollinators (estimated here as average per-flower visitation rates) modulated density-dependent pollination interactions. Pollinator visitation depended on conspecific and heterospecific flower density, with rare plants subjected to interspecific competition at the plot-level and interspecific facilitation at the site-level. Such interspecific competition at the plot-level was stronger for plants pollinated by diverse insects, while interspecific facilitation at the site-level was stronger for bee-pollinated plants. Moreover, we also found stronger positive conspecific density-dependence for plants with lower floral attractiveness at the site-level, meaning that they become more frequently visited when abundant. Our study indicates that the role of pollination in maintaining rare plants and plant diversity depends on the balance of density-dependent processes in species-rich communities. We show here that such balance is modulated by scale, pollination niches and floral attractiveness to pollinators, indicating the context-dependency of diversity maintenance mechanisms.

Not just flowering time: a resurrection approach shows floral attraction traits are changing over time.

Contemporary anthropogenic changes in climate and landscape form a complex set of selective pressures acting on natural systems, yet, in many systems, we lack information about both whether and how organisms may adapt to these changes. In plants, research has focused on climate-induced changes in phenology and the resultant potential for disruption of plant-pollinator interactions, however, there remains a paucity of knowledge regarding how other pollinator-mediated traits may be involved in the adaptive response. Here, we use resurrection experiments to investigate the phenotypic basis of adaptation in a mixed-mating system plant, the common morning glory (Ipomoea purpurea). Specifically, we measure temporal and spatial changes in traits grouped into three categories relevant to plant-pollinator interactions - floral morphology, floral rewards, and floral phenology. We show a significant temporal increase in corolla size and shift to earlier flowering times, as well as a potential for increased investment in floral rewards, all of which are driven primarily by populations at more northern latitudes. Additionally, we find evidence for directional selection on floral morphology and phenology and evidence of balancing selection acting on anther-stigma distance. Overall, these results show an adaptive response in line with greater investment in pollinator attraction rather than self-pollination and fine-scale spatial differences in adaptive potential.

Features of floral odor and nectar in the distylous Luculia pinceana (Rubiaceae) promote compatible pollination by hawkmoths.

It is hypothesized that in heterostylous plant species, standardization of signals of floral attraction between different morphs is advantageous, encouraging flower visitors to switch between morphs. It remains unclear whether signals of floral attraction (floral odor and properties of nectar) are similar between morphs in distylous species pollinated by hawkmoths, and how these relate to hawkmoth behavior. We observed the behavior of visitors to distylous Luculia pinceana (Rubiaceae), collected and analyzed floral odor, and examined properties of nectar (volume, sugar concentration, and composition) of long-styled and short-styled morphs during the day and night. Pollinator responses to the floral scent were tested with a Y-tube olfactometer. We conducted diurnal and nocturnal pollination treatments and six other pollination treatments to test the importance of nocturnal pollinators and to examine the self-incompatibility system. A species of hawkmoth, Cechenena lineosa, was the effective pollinator. The floral odor was rich in methyl benzoate, and sucrose was dominant in the nectar. There were no significant differences between the two morphs in the methyl benzoate content or the properties of nectar. Flowers released more methyl benzoate and secreted larger volumes of nectar with lower sugar concentration at night than during the day. The hawkmoth had a significant preference for methyl benzoate. Luculia pinceana was partially self-incompatible and relied on nocturnal pollinators for reproductive success. This study verifies that floral attraction signals are consistent between different morphs in this distylous species, promoting compatible pollination, and the features and the diel pattern of these signals between day and night are adapted to hawkmoth behavior.

Osmophore patterns in Ipomoea asarifolia (Desr.) Roem. & Schult. (Convolvulaceae)

To achieve reproductive fitness, floral attractants are essential for insect-plant interaction. Many entomophilous pollination plants have odorous zones, composed of glands that release volatile odors, these odors act as attractants for potential pollinators. Ipomea Asalifoila flowers were used for this study. One of its main characteristics is its infundibuliform morphology and glabrous leaves, and its reproductive structures are located in the center of the flower. In order to better understand the dynamics of the release of these odors, Ipomea A. flowers were collected to perform the test in neutral red 60%, and photographed before, during and after the procedure. These flowers were enveloped and separated by day of anthesis, from the first to the third day, where floral death occurred. After the tests, variations in the days of anthesis of the flowers were observed, with a gradual effect. Besides an osmotic concentration in their reproductive organs.

Phenology and Floral Biology of Diospyros sericea A. DC. (Ebenaceae): Inconstant Males May Be behind an Enigma of Dioecy.

Diospyros sericea is a tree/shrub species considered dioecious and broadly distributed in Brazil. Despite its importance for niche composition in a range of ecosystems, there is little knowledge about this species, and so far no study has analyzed its sexual system. We aimed to investigate dioecy expression in D. sericea through sexual dimorphisms in its phenology and floral biology. We analyzed the phenological events over a year and studied floral biology traits (morphology, flower development, floral resource, floral attractants supply, viability of pollen, and stigma receptivity) in both male and female plants. D. sericea presents typical features of dioecious plants like well-established primary and secondary dimorphisms that contribute to its reproductive success. However, we also identified fruit development in what should be structurally male individuals. We suggest that the evolutionary pathway leading to the observed phenomenon may be the existence of subdioecious populations with “inconstant males”. Although our data prevented us from making further assumptions about the origin of this trait, the study contributes to future analyses towards unraveling the enigma of dioecy not only in D. sericea but in other Diospyros species.

Florivory in twoChamaecristaspecies: Are secretory trichomes effective against florivores?

AbstractFlorivory inChamaecristavaries in occurrence, intensity, and the floral structures affected. As flowers are multifunctional units, the type of damage can impact reproductive success in different ways. Oil‐resin‐secreting trichomes, present in the sepals ofChamaecristaspecies, section Absus, are suggested to inhibit florivory. We recorded florivory inChamaecrista catharticaandChamaecrista catharticoidesin order to determine the frequency of damage, floral whorls most damaged, impact on reproduction, and effectiveness of secretory trichomes in inhibiting florivory. The study was conducted in the Parque Estadual do Ibitipoca, Brazil. Twenty individuals of each species were monitored monthly over two bloom periods to record the flowering intensity, rates of florivory, and fruit set and to determine the effectiveness of trichomes in inhibiting florivory. The two species had different flowering patterns, annual forC. catharticaand continuous forC. catharticoides, both more intense during summer. Florivory occurred mainly in the winter and affected floral structures unevenly, resulting in loss of different floral functions. Florivory reduced the fruit set of both species, butC. catharticoideswas considerably more impacted. The diversity of damaged structures inC. catharticoidesresulted in direct (reduced female and male fitness due to loss of ovules and pollen grains) and indirect (loss of floral resources and reduced floral attractiveness) impacts. Damage to the tubular petal could further result in loss of specialized pollination mechanisms mediated by this structure. Secretory trichomes on the abaxial surface of sepals inhibited florivory of buds and herbivory of early‐developing fruits.

The effects of florivory on floral attractiveness and fruit production in Daustinia montana (Convolvulaceae)

• Florivory affects floral attractiveness in Daustinia montana . • Pollinator visits decrease when corolla damage increases in Daustinia montana . • Fruit production under natural conditions was greater among intact flowers. Floral attractiveness is a strong determinant of pollination success, although the same attributes that attract pollinators can also attract florivores. Consumption of the corolla and/or reproductive structures can reduce pollinator visitation frequencies and depress fruit and/or seed set. We hypothesized that florivory would negatively affect the visitation frequencies of floral visitors and natural fruit set in Daustinia montana , a herbaceous species endemic to Brazil. We collected inflorescences of D. montana and recorded the numbers of floral structures with signs of florivory, as well as the locations of that damage, to quantify natural florivory. Artificial damage experiments were carried out with the corollas and stamens to experimentally determine the influence of florivory on the frequency of floral visits. We also randomly marked intact flowers and those naturally damaged by florivory and measured fruit set. More intact floral buds were observed under natural conditions than buds damaged by florivory. We observed that all of the analyzed structures (stamens/pistil and corolla) are generally attacked simultaneously, as opposed to only one specific structure. Intact flowers (controls) demonstrated greater rates of pollinator visitation than experimentally damaged flowers. The visitation frequencies of nectar thieves were not different between intact flowers and artificially damaged flowers. Fruit set under natural conditions was greater for intact flowers than for those that had experienced natural florivory. Our data indicated that floral damage had negative effects on floral attractiveness to pollinators. The greater natural production of fruits from intact flowers is indicative of the degree to which florivory can impact plant reproduction.

Long‐term experimental drought alters floral scent and pollinator visits in a Mediterranean plant community despite overall limited impacts on plant phenotype and reproduction

Abstract Pollinators are declining globally, with climate change implicated as an important driver. Climate change can induce phenological shifts and reduce floral resources for pollinators, but little is known about its effects on floral attractiveness and how this might cascade to affect pollinators, pollination functions and plant fitness. We used an in situ long‐term drought experiment to investigate multiple impacts of reduced precipitation in a natural Mediterranean shrubland, a habitat where climate change is predicted to increase the frequency and intensity of droughts. Focusing on three insect‐pollinated plant species that provide abundant rewards and support a diversity of pollinators (Cistus albidus, Salvia rosmarinus and Thymus vulgaris), we investigated the effects of drought on a suite of floral traits including nectar production and floral scent. We also measured the impact of reduced rainfall on pollinator visits, fruit set and germination in S. rosmarinus and C. albidus. Drought altered floral emissions of all three plant species qualitatively, and reduced nectar production in T. vulgaris only. Apis mellifera and Bombus gr. terrestris visited more flowers in control plots than drought plots, while small wild bees visited more flowers in drought plots than control plots. Pollinator species richness did not differ significantly between treatments. Fruit set and seed set in S. rosmarinus and C. albidus did not differ significantly between control and drought plots, but seeds from drought plots had slower germination for S. rosmarinus and marginally lower germination success in C. albidus. Synthesis. Overall, we found limited but consistent impacts of a moderate experimental drought on floral phenotype, plant reproduction and pollinator visits. Increased aridity under climate change is predicted to be stronger than the level assessed in the present study. Drought impacts will likely be stronger and this could profoundly affect the structure and functioning of plant–pollinator networks in Mediterranean ecosystems.

Mutualism has its limits: consequences of asymmetric interactions between a well-defended plant and its herbivorous pollinator.

Concern for pollinator health often focuses on social bees and their agricultural importance at the expense of other pollinators and their ecosystem services. When pollinating herbivores use the same plants as nectar sources and larval hosts, ecological conflicts emerge for both parties, as the pollinator's services are mitigated by herbivory and its larvae are harmed by plant defences. We tracked individual-level metrics of pollinator health-growth, survivorship, fecundity-across the life cycle of a pollinating herbivore, the common hawkmoth, Hyles lineata, interacting with a rare plant, Oenothera harringtonii, that is polymorphic for the common floral volatile (R)-(-)-linalool. Linalool had no impact on floral attraction, but its experimental addition suppressed oviposition on plants lacking linalool. Plants showed robust resistance against herbivory from leaf-disc to whole-plant scales, through poor larval growth and survivorship. Higher larval performance on other Oenothera species indicates that constitutive herbivore resistance by O. harringtonii is not a genus-wide trait. Leaf volatiles differed among populations of O. harringtonii but were not induced by larval herbivory. Similarly, elagitannins and other phenolics varied among plant tissues but were not herbivore-induced. Our findings highlight asymmetric plant-pollinator interactions and the importance of third parties, including alternative larval host plants, in maintaining pollinator health. This article is part of the theme issue 'Natural processes influencing pollinator health: from chemistry to landscapes'.

Ornithophily in the subtribe Maxillariinae (Orchidaceae) proven with a case study of Ornithidium fulgens in Guatemala

Ornithophily has been long speculated to occur in the subtribe Maxillariinae (Orchidaceae), relying either solely on micromorphological analyses or scarce field observations of undefined species. In Guatemala we were able to observe regular visits of the azure-crowned hummingbirds feeding on flowers of Ornithidium fulgens. These observations have led us to investigation of floral attractants by means of scanning and transmission microscopy, histochemical and chemical analyses (GC–MS). Conducted investigation revealed that the epidermis of basal protuberance of column-foot has features proving the secretory activity and that secreted nectar is sucrose-dominant. Slight secretion on the middle part of the lip is puzzling. The presence of other potential pollinators has not been reported. Based on the results of this study, we confirmed that the flowers of O. fulgens meet all criteria of ornithophily and thus that the hypothesis about bird pollination in the subtribe Maxillariinae is proven. The presented results confirm that the previously described floral features predicting the bird pollination in this group are justified. This strengthens the theory about floral adaptations to different pollinators and gives valid reasons to consider species with flowers with a certain set of traits as ornithophilous, even in the absence of the pollination observation.

Evolutionary breakdown of distyly to homostyly is accompanied by reductions of floral scent inPrimula oreodoxa

AbstractReproductive traits that function in pollinator attraction may be reduced or lost during evolutionary transitions from outcrossing to selfing. Although floral scent plays an important role in attracting pollinators in outcrossing species, few studies have investigated associations between floral scent variation and intraspecific mating system transitions. The breakdown of distyly to homostyly represents a classic example of a shift from outcrossing to selfing and provides an opportunity to test whether floral fragrances have become reduced and/or changed in composition with increased selfing. Here, we evaluate this hypothesis by quantifying floral volatiles using gas chromatography‐mass spectrometry in two distylous and four homostylous populations ofPrimula oreodoxaFranchet, a perennial herb from SW China. Our analysis revealed significant variation of volatile organic compounds (VOCs) among populations ofP. oreodoxa. Although there was no difference in VOCs between floral morphs in distylous populations as predicted, we detected a substantial reduction in VOC emissions and the average number of scent compounds in homostylous compared with distylous populations. A total of 12 compounds, mainly monoterpenoids and sesquiterpenoids, distinguished homostylous and distylous morphs; of these, (E)‐β‐ocimene was the most important in contributing to the difference in volatiles, with significantly lower emissions in homostyles. Our findings support the hypothesis that the transition from outcrossing to selfing is accompanied by the loss of floral volatiles. The modification to floral fragrances inP. oreodoxaassociated with mating system change might occur because high selfing rates in homostylous populations result in relaxed selection for floral attractiveness.

Cypripedium lichiangense (Orchidaceae) mimics a humus-rich oviposition site to attract its female pollinator, Ferdinandea cuprea (Syrphidae).

Most species in the genus Cypripedium (Cypripedioideae) produce trap flowers, making it a model lineage to study deceptive pollination. Floral attractants in most species studied appear to target bee species of different sizes. However, more recent publications report fly pollination in some subalpine species, suggesting novel suites of adaptive floral traits. Cypripedium lichiangense (section Trigonopedia) is an endangered subalpine species endemic to the Hengduan Mountains, China. We observed and analysed its floral traits, pollinators and breeding systems over 2 years insitu and in the lab. Cypripedium lichiangense was visited by females of Ferdinandea cuprea (Syrphidae). The pollinia were carried dorsally on the fly thoraces. The eggs of this fly were frequently found in the saccate labellum and on other floral organs, suggesting brood-site mimesis. The orchid is self-compatible, but cross-pollination produces more viable embryos. We propose a new mode of floral mimesis, humus-rich oviposition site mimicry, for C. lichiangense. Compared with the mimesis of aphid colonies attracting syrphid pollinators (subfamily Syrphinae), whose larvae are entomophagic, as reported in some Paphiopedilum species (Cypripedioideae), pollination by deceit in C. lichiangense represents a distinct and separate mode of exploitation of another saprophagic (or phytophagic) larvae syrphid lineage in the subfamily Eristalinae and appears to indicate diversity of pollination strategies in SectionTrigonopedia of Cypripedium. However, this new brood-site mimesis seems to be less attractive to pollinators. As a possible adaptation to the weak attracted pollination strategy, this plant species has a long flowering period and extended lifespan of individual flowers to ensure reproductive success.

Construction of Yeast One-Hybird Library for Screening of Eugenol Synthase Gene Bait vectors in Rosa chinensis

Roses are cultivated as ornamental plants in gardens, cut flowers and potted flowers, but also serviced in the perfume industry. Rose flowers product different volatile compounds including eugenol, being floral attractant for pollinators and used as an important composition of essential oil. Here, the eugenol synthase gene (RcEGS1) promoter was cloned from R. chinensis 'Old Blush'. The sequences of RcEGS1 promoter were 1776bp, contained the conserved elements, and predicted to be with several cis-regulatory elements involved in secondary metabolism of plants. Yeast one-hybrid library of R. chinensis 'Old Blush' at flower opening was constructed with the three-frame reading. The library capacity was more than 1.12×107CFU. The length of fragments inserted was 1 Kb to 3 Kb, which is fully meeting the demand of selecting the yeast library. The bait yeast vectors with cis-transcription elements MBS-box, G-box and one fragment bait yeast vectors were constructed, respectively. Furthermore, the transcript factors R2R3-type MYB and bHLH3 were screened using the yeast one-hybrid system. The results suggested the two TFs might play an important role in the pathway of volatile biosynthesis in roses.

A sophisticated case of division of labour in the trimorphic stamens of the Cassia fistula (Leguminosae) flower.

Buzz-pollinated pollen flowers have pollen as the primary resource for pollinators and must deal with a conflict between the exploitation of pollen grains by bees and pollination success. It has been hypothesized that heterostemony allows division of labour between stamens as a solution to the pollen dilemma. To test the division of labour hypothesis, we chose Cassia fistula, which has a trimorphic androecium and analysed androecium development, pollen grain release mechanisms and visitor behaviour. We explored the reflectance of floral organs and carried out an exclusion experiment to test the attractiveness of each stamen morph to the bee species. Finally, we explored the structural, ultrastructural and functional variation between the pollen grains, including pollen viability across stamen morphs. The differences among the three stamen morphs, which is developed from two whorls of the stamen, are the first evidence of the division of labour in our study system. Large Bombus and Xylocopa bees actively and exclusively exploited the pollen grains from the central poricidal anthers generating pollen deposition on their bodies. The reflectance pattern of floral organs indicated a targeting of these large bees to the central anthers, corroborated by the anther manipulative experiment where only the exclusion of the anthers positioned in the flower centre, especially the intermediate stamens, reduced bee visits. Both results revealed a division of labour, in which the intermediate stamen morph was responsible for both floral attractiveness and pollen resources. Only the largest stamen morph produced germinable pollen grains, highlighting their role as pollinating stamens. The smallest stamen morph has a less clear function, likely representing an economy in pollen production for feeding function. Our findings suggest that the evolution of the trimorphic androecium is associated with division of labour in large pollen flowers and can represent a strong strategy for circumventing the pollen dilemma, optimizing the feeding function by reducing pollen grain investment from central anthers.