Flower Opening Research Articles

Pollen collection by honey bee hives in almond orchards indicate diverse diets

Almond is one of the world's most economically valuable crops and many varieties require cross pollination for optimal fruit set. For this reason, western honey bee (Apis mellifera L.) hives are often placed in almond orchards. However, little is known about the usage of almond and other pollen sources by individual hives during almond bloom. Here, we investigated the timing, identity and quantity of pollen collection associated with almond floral abundance and spatial location of individual hives by sampling 440 individual pollen tray samples and counting 45,072 pollen grains from 13,200 pollen pellets collected from 80 individual hives across the flowering season in Victoria, south-eastern Australia. A large proportion of hives collected non-almond pollen in addition to almond pollen (63/80 = 79%). The weight of almond pollen collected by the hives at each sampling time was positively related to the number of concurrently open almond flowers. However, non-almond pollen richness and abundance was not related to the number of almond flowers but had a positive relationship with the weight of almond pollen collected. There was no relationship between the distance among hives and identity of pollen collected. Yet, three plant families in the study area were found to account for a high percentage of the non-almond pollen collected, Euphorbiaceae, Fabaceae and Asteraceae. Understanding crop and non-crop pollen collection could inform honey bee diet needs and identify the plant species of importance to inform best practice bee management during almond flowering.

MiR167d-ARFs Module Regulates Flower Opening and Stigma Size in Rice

Flower opening and stigma exertion are two critical traits for cross-pollination during seed production of hybrid rice (Oryza sativa L.). In this study, we demonstrate that the miR167d-ARFs module regulates stigma size and flower opening that is associated with the elongation of stamen filaments and the cell arrangement of lodicules. The overexpression of miR167d (OX167d) resulted in failed elongation of stamen filaments, increased stigma size, and morphological alteration of lodicule, resulting in cleistogamy. Blocking miR167d by target mimicry also led to a morphological alteration of the individual floral organs, including a reduction in stigma size and alteration of lodicule cell morphology, but did not show the cleistogamous phenotype. In addition, the four target genes of miR167d, namely ARF6, ARF12, ARF17, and ARF25, have overlapping functions in flower opening and stigma size. The loss-of-function of a single ARF gene did not influence the flower opening and stigma size, but arf12 single mutant showed a reduced plant height and aborted apical spikelets. However, mutation in ARF12 together with mutation in either ARF6, ARF17, or ARF25 led to the same defective phenotypes that were observed in OX167d, including the failed elongation of stamen filaments, increased stigma size, and morphological alteration of lodicule. These findings indicate that the appropriate expression of miR167d is crucial and the miR167d-ARFs module plays important roles in the regulation of flower opening and stigma size in rice.

Testing candidate genes linked to corolla shape variation of a pollinator shift in Rhytidophyllum (Gesneriaceae).

Floral adaptations to specific pollinators like corolla shape variation often result in reproductive isolation and thus speciation. But despite their ecological importance, the genetic bases of corolla shape transitions are still poorly understood, especially outside model species. Hence, our goal was to identify candidate genes potentially involved in corolla shape variation between two closely related species of the Rhytidophyllum genus (Gesneriaceae family) from the Antilles with contrasting pollination strategies. Rhytidophyllum rupincola has a tubular corolla and is strictly pollinated by hummingbirds, whereas R. auriculatum has more open flowers and is pollinated by hummingbirds, bats, and insects. We surveyed the literature and used a comparative transcriptome sequence analysis of synonymous and non-synonymous nucleotide substitutions to obtain a list of genes that could explain floral variation between R. auriculatum and R. rupincola. We then tested their association with corolla shape variation using QTL mapping in a F2 hybrid population. Out of 28 genes tested, three were found to be good candidates because of a strong association with corolla shape: RADIALIS, GLOBOSA, and JAGGED. Although the role of these genes in Rhytidophyllum corolla shape variation remains to be confirmed, these findings are a first step towards identifying the genes that have been under selection by pollinators and thus involved in reproductive isolation and speciation in this genus.

Microbiomes Associated With the Surfaces of Northern Argentinian Fruits Show a Wide Species Diversity.

The fiber, vitamin, and antioxidant contents of fruits contribute to a balanced human diet. In countries such as Argentina, several tropical fruits are witnessing a high yield in the harvest season, with a resulting surplus. Fruit fermentation using autochthonous starter cultures can provide a solution for food waste. However, limited knowledge exists about the microbiota present on the surfaces of fruits and the preceding flowers. In the present exploratory study, the microbiomes associated with the surfaces of tropical fruits from Northern Argentina, such as white guava, passion fruit and papaya were investigated using a shotgun metagenomic sequencing approach. Hereto, one sample composed of 14 white guava fruits, two samples of passion fruits with each two to three fruits representing the almost ripe and ripe stage of maturity, four samples of papaya with each two to three fruits representing the unripe, almost ripe, and ripe stage of maturity were processed, as well as a sample of closed and a sample of open Japanese medlar flowers. A considerable heterogeneity was found in the composition of the fruits’ surface microbiota at the genus and species level. While bacteria dominated the microbiota of the fruits and flowers, a small number of the metagenomic sequence reads corresponded with yeasts and filamentous fungi. A minimal abundance of bacterial species critical in lactic acid and acetic acid fermentations was found. A considerable fraction of the metagenomic sequence reads from the fruits’ surface microbiomes remained unidentified, which suggested that intrinsic species are to be sequenced or discovered.

Lilac (Syringa oblata) genome provides insights into its evolution and molecular mechanism of petal color change

Color change during flower opening is common; however, little is understood on the biochemical and molecular basis related. Lilac (Syringa oblata), a well-known woody ornamental plant with obvious petal color changes, is an ideal model. Here, we presented chromosome-scale genome assembly for lilac, resolved the flavonoids metabolism, and identified key genes and potential regulatory networks related to petal color change. The genome assembly is 1.05 Gb anchored onto 23 chromosomes, with a BUSCO score of 96.6%. Whole-genome duplication (WGD) event shared within Oleaceae was revealed. Metabolome quantification identified delphinidin-3-O-rutinoside (Dp3Ru) and cyanidin-3-O-rutinoside (Cy3Ru) as the major pigments; gene co-expression networks indicated WRKY an essential regulation factor at the early flowering stage, ERF more important in the color transition period (from violet to light nearly white), while the MBW complex participated in the entire process. Our results provide a foundation for functional study and molecular breeding in lilac.

A daylength-neutral winged bean (Psophocarpus tetragonolobus) for Southern Australian latitudes

Abstract. Eagleton GE. 2022. A daylength-neutral winged bean (Psophocarpus tetragonolobus) for Southern Australian latitudes. Asian J Agric 6: 68-78. In the summer of 2019, on the central coast of NSW, Australia (at Latitude 34°S), an early-maturing genotype of the tropical legume crop, winged bean (Psophocarpus tetragonolobus (L.) DC.), was detected among a range of late-maturing accessions. The performance of this accession, MY0-01 from Bago in Myanmar, was evaluated in staked plots alongside one other accession from Myanmar and two from the island of New Guinea planted on three successive occasions between October and late November 2020 in a split-plot experiment. Across the three planting dates, the mean number of days from planting to the first open flower for MYO-01 ranged from 68 to 82 + s.e. 3.2 compared with a range of 119 to 167 for the other three accessions. The mean accumulated seed yield of MYO-01 obtained from the October planting equated to 3.1 t ha-1, but by the third planting in late November, the yield was only half as much. Among the four accessions, MYO-01 was second in the amount of lower stem branching and tuber yield, with the smallest pods and hardest seeds. Hard seededness creates difficulties for germination and plant establishment and is a limitation in MYO-01, as are its small pods, which lowers its potential for vegetable production. Investigating genetic control of photoperiod insensitivity in MYO-01 and combining the ability for pod and seed characteristics is relevant to sub-tropical latitudes and for developing stable early maturity cultivars for the tropics.

Bioactivities of Phenylpropanoids Extracted from Ephemeral Flowers of Medicinal Woody Species Murraya paniculata (Linn.) Jack

Flowers of Murraya paniculata were assessed for production of phenolic secondary metabolites and were found to yield temporally variable concentrations of total phenolics and flavonoids due to enzymatic regulation by L-phenylalanine ammonia lyase. Maximum yield of phenolics was obtained from partly open flowers, with esterified hydroxycinnamic acids (mainly ferulic acid) forming the major component. Scopoletin-a coumarin product of ferulic acid - was isolated consistently from senescent flowers by High Performance Liquid Chromatography (HPLC). Approximately 200 mg of fresh floral tissue extracted with one millilitre solvent (methanol:water :: 30:70) yielded up to 1.6 mg of ferulic acid and 40 μg of scopoletin from partly open (at 18:00 h) and senescent (at 06:00 h) blooms respectively. Along with other hydroxycinnamic acid and coumarin components of M. paniculata flowers detected by HPLC, o-coumaric acid and isoauraptene were identified by Gas Chromatography-Mass Spectrometry. Various free-radical scavenging assays revealed the ferulic acid fraction to have stronger antioxidant activities than the scopoletin fraction, but no antibiotic activity was detected for ferulic acid. Total antioxidant capacities of ferulic acid and scopoletin fractions were estimated to be 9% and 7.8% of that of ascorbic acid standard, respectively. Scopoletin fraction exhibited Minimum Inhibitory Concentrations at 0.585 mg.mL-1 against Bacillus subtilis and 1.372 mg.mL-1 against Escherichia coli. The high concentrations of these bioactive phenylpropanoids in such a common flower species presents potential application in low-risk crop protection and plant-based nutraceuticals.

Floral biology, breeding system and pollination ecology of Justicia betonica L. (Acanthaceae): An assessment of its low reproductive success in West Bengal, India

AbstractBesides its importance as an ornamental plant, Justicia betonica L. is also used as a medicinal plant for the treatment of several human disorders. However, the population size and abundance of the plant species are very low in Indian states, including West Bengal. The breeding system and pollination ecology of J. betonica are still unclear. Therefore, some reproductive aspects were investigated in order to provide important information for the sustainability of the species. The flowering duration spanned from December to May, with its peak in February–March. Flower opening time was much earlier (5.00–8.00 a.m.) on a hot day (in April–May) than on a cold day (10.00 a.m.–12.00 p.m. in December–January). The time of anther dehiscence coincided with the flower opening time; however, the stigma became receptive later. The plant species is self‐compatible but dependent on pollinators for fruit and seed sets. Members of different insect groups like ants, bees, butterflies, flies, moths and wasps visit the flowers. Among them, Allorhynchium metallicum and Halictus acrocephalus are the primary pollinators (based on the “relative pollinator service”). The plant species showed a significant pollination deficit (coefficient of pollination deficit [D] = 0.32) in the open condition. Larvae of the florivorous moth Gatesclarkeana erotias significantly reduced reproductive success by eating their floral parts, ovules and immature seeds. In conclusion, combining the pollination deficit and the feeding activity of phytophagous insects (moth larvae) may reduce the reproductive fitness of J. betonica in the study regions.

Effect of Developmental Stages on Genes Involved in Middle and Downstream Pathway of Volatile Terpene Biosynthesis in Rose Petals.

Terpenoids are economically and ecologically important compounds, and they are vital constituents in rose flower fragrance and rose essential oil. The terpene synthase genes (TPSs), trans-prenyltransferases genes (TPTs), NUDX1 are involved in middle and downstream pathway of volatile terpene biosynthesis in rose flowers. We identified 7 complete RcTPTs, 49 complete RcTPSs, and 9 RcNUDX1 genes in the genome of Rosa chinensis. During the flower opening process of butterfly rose (Rosa chinensis ‘Mutabilis’, MU), nine RcTPSs expressed in the petals of opening MU flowers exhibited two main expression trends, namely high and low, in old and fresh petals. Five short-chain petal-expressed RcTPTs showed expression patterns corresponding to RcTPSs. Analysis of differential volatile terpenes and differential expressed genes indicated that higher emission of geraniol from old MU petals might be related to the RcGPPS expression. Comprehensive analysis of volatile emission, sequence structure, micro-synteny and gene expression suggested that RcTPS18 may encode (E,E)-α-farnesene synthase. These findings may be useful for elucidating the molecular mechanism of terpenoid metabolism in rose and are vital for future studies on terpene regulation.

Biological flora of Britain and Ireland:Neottia nidus‐avis

AbstractThis account provides information on all aspects of the biology ofNeottia nidus‐avis(L.) Rich. (Bird's‐nest Orchid) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of Britain and Ireland: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, reproductive characteristics, herbivory, history and conservation.Neottia nidus‐avisis a native mycoheterotrophic orchid; it is found most frequently in the deep humus of densely shaded beech woodlands, on limestone or chalky soils in the British Isles. The species extends throughout temperate Eurasia.Neottia nidus‐avisis a perennial, mostly monocarpic herb with mixed mode of reproduction and many adaptations to autogamy. The perennating organ is a short rhizome; vegetative reproduction by rhizome branching or root‐sprouting is rather infrequent. Because of its achlorophyllous nature,N. nidus‐avisis entirely dependent on its mycorrhizal basidiomycetes from the family Sebacinaceae for nutrition.Plastid genome ofN. nidus‐avishas been reduced as a result of the relaxation of functional constraints on photosynthesis as in other mycoheterotrophic plants. Despite this, the plant has retained all enzymes to produce chlorophyll as well as some photoprotective metabolites, such as zeaxanthin and tocopherol, whose function in the mycoheterotrophic plant remains unresolved.The species flowers from May to June, depending on latitude and altitude. The flowers emit a sweet scent and produce little nectar. They may be pollinated by flies, crawling thrips and ants but self‐pollination is presumed to be the main mode of reproduction. Between 75% and 97% of open flowers set fruits.Neottia nidus‐avisis classified asVulnerablein Great Britain. The species is scattered throughout much of the British Isles, but it is very scarce except in southern England, where it is locally abundant. The main threats are deforestation, changes in woodland management and coniferization.

Longevity and post-harvest quality of cut ornamental sunflower floral

The postharvest quality and longevity of cut flowers is influenced by several factors, with the development stage being one of the determining aspects. The determination of the harvest point is variable and must be carried out depending on the physiology of flower development and the proximity of the consumer market. In this sense, the objective was to determine the harvesting point and the ideal stem length for harvesting ‘Sol Vermelho’ ornamental sunflower. The experimental design adopted was completely randomized, arranged in a 2 × 4 factorial scheme (harvest point × stem length), where stems harvested at stages R4 and R5.5 and in four lengths of 50, 60, 70, and 80 cm were used. The results demonstrate that the early harvest (R4 stage) of the ornamental sunflower flower ‘Sol Vermelho’ stems is a viable alternative that allows greater post-harvest durability and, consequently, the commercialization of the stems for a longer period of time. In addition, stems harvested at stage R5.5 (open flowers) with lengths of 50 and 60 cm can be recommended for sale in regions close to the production sites.

Living in the shadows: Gastrodia orchids lack functional leaves and open flowers

Non‐photosynthetic plants dependent on fungi have long fascinated botanists and mycologists. The genus Gastrodia (Orchidaceae) contains more than 100 achlorophyllous species, including some species recently discovered in Japan and Taiwan which produce only closed self‐pollinating flowers. To date, Gastrodia is probably the only genus containing species with only closed flowers, which has been verified by a decade of monitoring hundreds of individuals. Here, the unique characteristics of the genus Gastrodia have been reviewed, emphasizing the reproductive biology of these newly described species that neither photosynthesize nor bloom. Investigation of such species that scarcely resemble other plants may paradoxically enhance our understanding of plants more broadly.

Effect of drought stress on flowering characteristics in rice (Oryza sativa L.): a study using genotypes contrasting in drought tolerance and flower opening time

ABSTRACT Rice is most susceptible to heat and drought stress at flowering stage, but flowering characteristics under drought stress are not well characterized. This study investigated flowering characteristics of rice genotypes contrasting in their flower opening time (FOT) and level of drought tolerance. Near-isogenic lines for the early-morning flowering trait (IR64+ qEMF3) and for drought tolerance (IR87707-445-B-B-B), and their recurrent parent cultivar (IR64) were used. IR64+ qEMF3 had stable earlier FOT than IR64 and IR87707-445-B-B-B under drought stress conditions. Drought stress occasionally affects FOT depending on genotype. The number of open spikelets was higher in IR87707-445-B-B-B than in IR64 and IR64+ qEMF3, and the difference among genotypes increased as the rice plants were subjected to more severe stress levels. Panicle temperature increased under drought stress conditions and was similar among genotypes when it was measured at the same time of day, demonstrating that earlier FOT in IR64+ qEMF3 must be beneficial to avoid heat stress at flowering under drought stress conditions. However, IR64+ qEMF3 did not exhibit drought avoidance, as evidenced by the root mass at depth. To assess the potential for the EMF trait to complement ongoing drought breeding efforts, heat tolerance among 13 advanced drought breeding lines and released cultivars was tested. Wide variation in heat tolerance at flowering was observed and, notably, none of the 13 lines possessed the EMF trait. This study therefore proposes that a breeding strategy that transfers the EMF trait into drought tolerant lines could enhance the resilience of rice spikelets to the combined stresses of heat and drought at flowering. Abbreviations: Analysis of variance (ANOVA), dry season (DS), early-morning flowering (EMF), flower opening time (FOT), near-isogenic line (NIL), panicle water potential (PWP), quantitative trait locus (QTL), wet season (WS)

Cloning and Functional Analysis of NtMYB9 in ‘Jinzhanyintai’ of Narcissus tazetta var. chinensis

Narcissus tazetta var. chinensis M.Roem. (Chinese Narcissus) is a traditional and famous flower in China, and its corona shows a transition from green to yellow with the opening of flowers, which is of great ornamental value. To investigate the molecular mechanism of the corona color-forming in the Chinese Narcissus, in this study, a MYB gene was screened from the transcriptome of the corona by bioinformatics analysis methods, named NtMYB9. The expression level of the NtMYB9 gene was significantly higher in the corona than in the tepal, filament, ovary and leaf, and reached the highest level at the fourth period of complete coloration of the corona. The full-length sequence of the NtMYB9 coding region was cloned using the corona cDNA as a template. Sequence analysis revealed that NtMYB9 protein contained R2 and R3 domains, phylogenetic tree analysis showed that the NtMYB9 protein was most closely related to flavonol activators. Subcellular localization showed that NtMYB9 was localized in the nucleus. The overexpression of NtMYB9 gene into tobacco leaves and the expression level of seven enzyme genes related to the flavonoid biosynthesis pathway were significantly up-regulated. The transient transformation of Petunia × hybrida (Petunia) and Phalaenopsis aphrodite (Phalaenopsis) significantly revealed that the NtMYB9 gene could turn flowers yellow. These results suggest that the NtMYB9 gene is involved in the positive regulation of flavonoid biosynthesis in the Chinese Narcissus and may promote the synthesis of flavonols. In conclusion, these findings provide a valuable resource for further studies on the regulatory mechanism of the flavonoid biosynthesis pathway, and they are also beneficial to the molecular breeding of Chinese Narcissus.

Mendelian inheritance of introrse orientated anthers in Brassica rapa

The inheritance of anther orientation of 154 individuals from two B<sub>1</sub> populations of Brassica rapa (syn. Brassica campestris) was evaluated under controlled conditions in a greenhouse. The anther orientation was evaluated visually at the time of fully open flowers. The observed extrorse:introrse ratios were 1 : 1 in R-o-18 × (R-o-18 × RM29) population and 3 : 1 in R-o-18 × (R-o-18 × R c-50) population. It was concluded that this trait is controlled by two duplicated pairs of genes (A<sub>1</sub>, A<sub>2</sub>) for extrorse anthers, either of which can produce extrorse anthers when a single dominant allele is present. Introrse anthers result when all alleles at both loci are recessive.

An Aux/IAA Family Member, RhIAA14, Involved in Ethylene-Inhibited Petal Expansion in Rose (Rosa hybrida).

Flower size, a primary agronomic trait in breeding of ornamental plants, is largely determined by petal expansion. Generally, ethylene acts as an inhibitor of petal expansion, but its effect is restricted by unknown developmental cues. In this study, we found that the critical node of ethylene-inhibited petal expansion is between stages 1 and 2 of rose flower opening. To uncover the underlying regulatory mechanism, we carried out a comparative RNA-seq analysis. Differentially expressed genes (DEGs) involved in auxin-signaling pathways were enriched. Therefore, we identified an auxin/indole-3-acetic acid (Aux/IAA) family gene, RhIAA14, whose expression was development-specifically repressed by ethylene. The silencing of RhIAA14 reduced cell expansion, resulting in diminished petal expansion and flower size. In addition, the expressions of cell-expansion-related genes, including RhXTH6, RhCesA2, RhPIP2;1, and RhEXPA8, were significantly downregulated following RhIAA14 silencing. Our results reveal an Aux/IAA that serves as a key player in orchestrating petal expansion and ultimately contributes to flower size, which provides new insights into ethylene-modulated flower opening and the function of the Aux/IAA transcription regulator.

Effect of Flavonoid Dynamic Changes on Flower Coloration of Tulipa gesneiana ‘Queen of Night’ during Flower Development

Tulipa gesneriana has rich cultivars with abundant flower colors; among them, black tulips have become precious cultivars for their rareness in nature. It is of great significance to understand its color formation mechanism for breeding new cultivars with a blackish flower color in the future. In this present study, petals at five developmental stages of Tulipa gesneriana ‘Queen of Night’ (shorted for ‘QN’), a typical black tulip cultivar, were collected to identity the flavonoid composition and compare the accumulation along with the flower development process, aiming to explore the metabolic mechanism of its flower coloration. By using UPLC-Q-TOF-MS, three anthocyanins and nineteen anthoxanthins (including eighteen flavonols and one flavone) were detected in the petals of ‘QN’. The anthocyanins were identified as delphinidin 3-o-rutinoside, cyanidin 3-o-rutinoside and pelargonidin 3-o-rutinoside, respectively. The main flavonols were identified as quercetin, kaempferol, isorhamnetin, naringin and their glycosides. The only one flavone substance was identified as an apigenin derivative. By comparing the content, anthocyanins were the most abundant substance in the petals of ‘QN’, and showed obvious regularity in the development process. With the flower opening, the anthocyanin content accumulated continuously, and reached the highest level at 3575.9 μg·g−1·FW at S5, accounting for 80% of the total flavonoids. Among them, delphinidin 3-o-rutinoside and cyanidin 3-o-rutinoside made the main contribution to the coloration of ‘QN’. The content of anthoxanthins increased first and then decreased, reaching the highest to 1114.8 μg·g−1·FW at S3. Quercetin and its glycosides were the most important flavonol substances in the petals of ‘QN’, accounting for more than 60% of the total anthoxanthins in the five stages. The content of a flavone identified was extremely low, suggesting a limited role in the flower color of ‘QN’. Taken together, the flower color presentation of ‘QN’ was closely related to the composition and accumulation of anthocyanins and flavonols; anthocyanins were the main substances that determine the petal coloration of ‘QN’, and the high content of flavonols played a role of co-pigmentation with these anthocyanins.

High-energy-level metabolism and transport occur at the transition from closed to open flowers.

During the maturation phase of flower development, the onset of anthesis visibly marks the transition from buds to open flowers, during which petals stretch out, nectar secretion commences, and pollination occurs. Analysis of the metabolic changes occurring during this developmental transition has primarily focused on specific classes of metabolites, such as pigments and scent emission, and far less on the whole network of primary and secondary metabolites. To investigate the metabolic changes occurring at anthesis, we performed multi-platform metabolomics alongside RNA sequencing in individual florets harvested from the main inflorescence of Arabidopsis (Arabidopsis thaliana) ecotype Col-0. To trace metabolic fluxes at the level of the whole inflorescence and individual florets, we further integrated these studies with radiolabeled experiments. These extensive analyses revealed high-energy-level metabolism and transport of carbohydrates and amino acids, supporting intense metabolic rearrangements occurring at the time of this floral transition. These comprehensive data are discussed in the context of our current understanding of the metabolic shifts underlying flower opening. We envision that this analysis will facilitate the introgression of floral metabolic traits promoting pollination in crop species for which a comprehensive knowledge of flower metabolism is still limited.

Better time of flower opening, a good time to improve the efficiency of hybrid seed production

The proper time of flower opening, which ensures successful pollination by exposure of stamens and gynoecia via petal movement, is locally adapted to diverse environmental changes among different plants (Cheng et al., 2021). Consequently, flower opening time may differ among divergent populations as a result of long-term adaptation, thereby promoting prezygotic reproductive isolation by preventing mating and hybridization.

A generalized bird pollination system in Schotia brachypetala (Fabaceae).

Bird pollination systems are diverse, ranging from narrow-tubed flowers pollinated by specialist nectarivores such as hummingbirds and sunbirds, to relatively open flowers pollinated by opportunistic (i.e. generalist) nectarivores. The role of opportunistic avian nectarivores as pollinators has historically been under-appreciated. A key aspect to understanding the importance of opportunistic birds as pollinators is to investigate how efficiently they transfer pollen among flowers. Here, we document the pollination and breeding systems of Schotia brachypetala, a southern African tree known as the 'weeping boer-bean' on account of its prolific production of dilute hexose-dominated nectar. The cup-shaped flowers of this tree attract a large number of bird species, including both opportunistic and specialist nectarivores. We identified floral visitors using observations and camera traps and quantified the floral traits responsible for animal attraction. We documented the breeding system, used selective pollinator exclusion to test the contribution of birds to fecundity, and performed supplemental pollination to test for pollen limitation. Single-visit pollen deposition trials were undertaken to determine the efficacy of bird pollinators. Controlled hand-pollination experiments showed that S. brachypetala is genetically self-incompatible and therefore dependent on pollinators for seed production. Supplemental hand-pollination experiments showed that natural fecundity is limited by either the amount and/or the quality of pollen on stigmas. Flowers from which birds but not insects were experimentally excluded set fewer seeds than open control flowers. Opportunistic birds deposited more pollen per visit than did specialist sunbirds. We conclude that S. brachypetala has a generalized bird pollination system that mainly involves opportunistic nectarivores.