Flower Sex Ratio Research Articles

Floral Characterization of Pomegranate Genotypes to Improve Hybridization Efficiency.

Pomegranate (Punica granatum) has staminate (male), androgynous (hermaphrodite), and intermediate flower types. Floral characterization is difficult for breeding efficiency across many pomegranate genotypes in Pakistan, which is essential for pomegranate cultivar enhancements. The present research focused on the floral characterization and breeding efficiency of fifteen pomegranate genotypes. Flower sex ratio, floral morphological parameters, i.e., flower length, ovary width, flower notch, flower tip and stigma with style length, and fruit set percentage were examined during the experiment. In terms of sex ratio, male flowers were found to be higher among all genotypes. Due to clear differences in flower length, width, and heterostyly facilitating visual identification of the hermaphrodite flowers, genotype Ternab-2, Kandhari White, and Kandhari Red had higher fruit set (≥70%) among all cross combinations attempted. Genotype Sava had higher flower length and heterostyly of hermaphrodite flower type, but ovary width was not very distinct, leading to average crossing success (85-34%). In conclusion, single or combination of morphological characters can be used for accurate identification of hermaphrodite flowers, which can improve hybrid efficiency and fruit set after artificial cross-pollination.

Assessment of weather effect on flower morphogenesis and fruit set in mango varieties in central India

A two-year field experiment was initiated in 2017-18 and 2018-19 years simultaneously to assess temperature on flower morphogenesis stages, flower sex ratio (hermaphrodite/staminate male flower) and fruit set in monoembryonic Langra and Amrapali varieties. Different dates of flower phenological stages viz., bud, panicle, bloom and flower initiation, pea, marble, egg, and maturity of fruits were recorded. The Langra variety exhibited bud initiation after mid December whereas Amrapali variety by the end of December. The range of mean maximum / minimum temperature as 26-31/10-12 °C promoted hermaphrodite flowers per panicle by 74 per cent in Langra variety, whereas range of 27-29/11-13 °C favored by 35 per cent in Amrapali variety. A positive and significant correlation between total number of flower / panicle and flower sex ratio in both the varieties suggested that higher temperature during initial flower phenologies improved number of hermaphrodite flowers. A mean minimum temperature for producing more number of hermaphrodite flower exhibited a range of 11-14 °C under central Indian conditions. Fruit set was maximum during pea stage and decline afterwards in marble and fruit maturity stages due to sudden rise in temperature at marble stage that caused in drop down of humidity thereby resulted in fruit drop in both the varieties.

Annual Population Dynamics and Their Influencing Factors for an Endangered Submerged Macrophyte (Ottelia cordata)

Due to wetland loss, Ottelia cordata (O. cordata, Wallich) Dandy has been categorized as an endangered species on the List of Key Protected Wild Plants in China. Quantifying the relative importance of demographic (i.e., growth, survival, and reproduction) and habitat preference traits on the population dynamics (abundance) of O. cordata could guide how to develop the best recovery strategies of O. cordata, yet currently, there are no studies that investigate this. By monitoring monthly changes in O. cordata abundance and demographic traits (plant height, leaf area, flower sex ratio, and seed number) that were highly correlated with growth rate, photosynthetic rate, and water depth, we identified several relationships. Linear mixed-effect models and variance partition quantified the specific effects of four demographic traits and water depth on O. cordata abundance in three habitat types (paddyfield, stream, and spring). The linear mixed-effect models indicate that among the four demographic traits, height could be significantly positively correlated to abundance in all three habitat types. In contrast, other three traits (leaf area, sex ratio, and seed numbers) were non-significantly associated with abundance across each habitat. Height was determined by water depth, so water depth rather than photosynthetic rate and reproduction rate may promote the development and recovery of O. cordata populations. Variance partition results showed that water depth mediated the positive influence of growth rate on the abundance of O. cordata in the living habitats (paddyfield and spring). In contrast, water depth but not growth rate determined the abundance of O. cordata in the living habitat (stream). However, water depth had a significantly negative impact on the abundance of O. cordata in stream habitats, likely because all of the streams were shallow. Altogether, in the short term for avoiding the potential harm or even extinction of O. cordata, keeping appropriate water depth or transplanting O. cordata to spring should be an effective strategy because the water is not only deep enough but also clear in spring habitats. Additionally, water turbidity was shown to affect the density of O. cordata growth, wherein O. cordata was sparsely distributed when turbidity was high. Therefore, in the long run, to make the population gradually recovery, it will be necessary to restore the degraded wetland. This could be accomplished by reducing water pollution and removing sludge to reduce turbidity and increase hydrological connectivity.

Seasonal change of flower sex ratio and pollinator dynamics in three reproductive ecotypes of protandrous plant

AbstractCimicifuga simplex has three genetically and ecologically distinct pollination morphs with different flowering phenology, flower sex expressions, and selfing rates. A previous study showed that strong protandry in hermaphroditic flowers of C. simplex causes there to be seasonal minority sexes; for example, unisexual female ramets are advantageous in the first half of the flowering season and bloom then (minority sex hypothesis). That study, however, did not distinguish among the three pollination morphs of C. simplex. We investigated seasonal sex ratio changes and pollinator environments of the three morphs to verify and expand the minority sex hypothesis. We investigated flowering phenology, pollinator quantity and quality, seasonal population sex ratio dynamics, and stamen/ovule ratios in hermaphroditic flowers. We also examined the seasonal female reproductive success of hermaphroditic flowers, and the effect of male flower excision on fruit set by morph II hermaphroditic flowers. Morph I (mainly hermaphroditic and female ramets) had high pollinator quality and quantity. Fruit set of hermaphroditic ramets was high throughout the flowering season. Morph II (hermaphroditic and andromonoecious ramets) had low pollinator quality, and few pollinators visited near the beginning and end of the season. Removal of male flowers led to a pollen limitation. Morph III (hermaphroditic ramets and a high selfing rate) had very low pollinator abundance throughout the flowering season, and male and female phases largely overlapped. The scarcity of male flowers in morph I is likely a result of the high pollinator quantity and quality. The high fruit set suggests that no pollen limitation existed. The low pollinator quality and quantity of the morph II population caused it to suffer from pollen limitation and may explain the absence of unisexual female ramets in this morph. The high selfing rate of morph III may be due to the extremely low pollinator abundance. Theoretical studies have indicated that the optimal investment allocation to male and female functions depends on whether a pollen limitation exists. In C. simplex, the observed relationships between pollinator environment and reproductive systems are consistent with these theoretical models.

Sex-Related Differences in Growth, Herbivory, and Defense of Two Salix Species

Sex-related differences in sex ratio, growth, and herbivory are widely documented in many dioecious plants. The common pattern is for males to grow faster than females and to be less well-defended against herbivores, but Salix is an exception. To study sex-related differences in the patterns of resource allocation for growth and defense in willows, we conducted a large-scale field experiment to investigate the flowering sex ratio, mortality, growth traits, insect herbivory and content of defensive substances in three Salix populations comprising two species. Results demonstrate that the two Salix suchowensis Cheng populations have a female bias in the sex ratio, whereas no bias is found in the S. triandra L. population. Male individuals in the S. suchowensis populations have significantly higher mortality rates than females. However, the mortality rate of S. triandra population has no gender difference. This finding may be one of the explanations for the difference in sex ratio between the two species. The females are larger in height, ground diameter, and biomass, and have a higher nutritional quality (N concentration) than males in both species. Nevertheless, slow-growing males have a higher concentration of the defense chemical (total phenol) and lower degrees of insect herbivory than females. Additionally, biomass is positively correlated with herbivory and negatively correlated with defense in the two willow species. It is concluded that the degrees of herbivory would have a great influence on resource allocation for growth and defense. Meanwhile, it also provides important implications for understanding the evolution of dioecy.

The dynamics of precipitation and its relation to flowering status and oil palm productivity

This paper exposes the relation between monthly precipitation amount dynamics with the assumably impacted flowering status of productive oil palm and its productivity in the next period. The observation was conducted in Jambi 2016-2017 and Kalimantan in 2017. Simple regression and Pearson’s correlation procedure was applied to calculate the relation between actual flower sex ratio as well as oil palm productivity. Under water scarcity conditions in the dry season, more flower infertility will be exposed in the same period of the dry season with higher response variability. Soil moisture content under the frond pile is more stabilized against evaporation so that the rate of soil demoisturizing at the upper horizon layer is slower than at the circle area and active path area. Estimated oil palm production in a period is determined by the precipitation value 36 months before harvest.

Overhead sprinkler irrigation affects pollinators and pollination in pumpkin (Cucurbita maxima)

Cucurbits are monoecious plants and most of them depend on pollinators for fruit set. However, studies suggest that pumpkin and squash fields are pollination deficient. Pollinator limitation, suboptimal flower sex ratio, and exploitative competition between invasive ants and bees are a few major suggested reasons for this. Pumpkin flowers have a corolla cup and secrete nectar throughout anthesis, which make them attractive to bees. In south India, honey bee (Apis cerana) is the major pollinator of pumpkin flowers. Like pollinators, water is also a limiting factor for growth and production of flowers in pumpkin. It has been suggested to use overhead sprinklers to irrigate and fertilize pumpkin fields. We hypothesized that the sprinkler affects the visitation characteristics of foraging bees in flowers and pollination, and so, we performed an experiment to test this. For this reason, we recorded pollinator visits on staminate and pistillate flowers for 15 min and poured water in the flower cups and examined the water retention time and the visitation characteristics of pollinators in both staminate and pistillate flowers, and fruit set in pistillate flowers. Water remained inside the staminate and pistillate flower cups until the flower senescence. Honey bees entered and foraged nectar/pollen in flowers during the waterless condition. In water-filled flowers, honey bees hovered around or landed only on the corolla and did not forage floral resources or contact the reproductive parts. As a consequence, none of the water-filled flowers developed fruits. Therefore, the overhead sprinkler irrigation, despite cover a large area effectively, may not be an appropriate irrigation method for pumpkin during flowering period.

Influence of girdling on flower sex ratio, biochemical constituents, and fruit set intensity in mango (Mangifera indica L.)

The study was conducted in mango to understand the relationship of various metabolites with flower sex ratio (hermaphrodite/male) and fruit set using stem girdling technique. Girdling one year old branches was carried out in two cultivars, Mangifera indica 'Alphonso' and 'Totapuri' to retain 50, 100 and 150 leaves to vary the content of hormones, sugars, total carbohydrates, and amino acids. The increased leaf number was found to increase the total carbohydrates, glucose, fructose, and other sugars. Girdling also significantly increased the concentration of abscisic acid (ABA), salicylic acid (SA), jasmonic acid (JA), indole acetic acid, indole butyric acid but decreased gibberellins and cytokinins. Amino acids also increased in the girdled branches. Girdling improved the flower sex ratio as well as fruit set more efficiently in 'Alphonso' than in 'Totapuri'. Results indicate that the increase in production of hermaphrodite flowers may be more related to the higher production of growth inhibitors, like ABA, SA, and JA along with increased concentration of sugars. Increased auxin concentration also might play an important role in increasing the fruit set.

Effect of flower sex ratio on fruit set in pumpkin (Cucurbita maxima)

Flower sex expression and sex ratio are the two plant functional traits likely to explain pollination efficiency in monoecious animal-pollinated plants. Cucurbitaceae crop plants are staminate flower-biased, but, relatively little is known about the natural variation in flower sex expression and the effect of flower sex ratio on fruit set. To address these, 325 plants of Cucurbita maxima were monitored for the entire flowering cycle and studied fruit set in 1515 pistillate flowers under open conditions for two years. The flower sex ratio of the fields and the plants and the flowering age (=phase) of the plants were used as the predictors of fruit set. The blooming in C. maxima started with the staminate flowers; 67% of the plants produced a staminate flower first, which continued for about ten days. The number of staminate flowers produced in the plants strongly predicted the number of pistillate flowers bloomed later. The sex ratio of the fields, rather than that of an individual plant, predicted the fruit set. Although pollinators are vital for pollination in animal-pollinated monoecious plants, our results suggest that flower sex ratio is also a crucial predictor of pollination efficiency. Monitoring flower sex expression in fields may be required to predict realistic fruit set and to take necessary measures, including facilitated pollination to improve fruit set.

Differences in flowering sex ratios between native and invasive populations of the seagrass Halophila stipulacea

Abstract Deviations from the 1:1 sex ratio are common in dioecious plants. The tropical seagrass Halophila stipulacea is among an extremely rare group of dioecious plants that are widely recognized as female-biased. Here we report on differences in sex ratios between native (Eilat, northern Red Sea) and invasive (Cyprus, Mediterranean Sea) populations. While H. stipulacea populations were female-biased in their native region, invasive populations were either male- or female-biased. The existence of both sexes simultaneously in the Mediterranean invasive populations might help its ongoing expansion in the Mediterranean, thereby threatening local seagrasses species.

Effects of soil properties and clonal growth on the apparent sex ratio of the flowering stems of the dioecious clonal shrub Aucuba japonica var. borealis growing in an evergreen coniferous secondary forest

In dioecious plants, the frequencies of flowering stems in each sex produced through clonal growth provide important information on the potential for reproductive success in the populations. However, apart from the light environment in their habitat, the factors affecting the flowering of each sex have not been well documented in shrub species that can maintain their populations in shady environments. In this research, we investigated seven soil variables and the flowering of stems of Aucuba japonica var. borealis in patches of this dioecious clonal shrub with different apparent stem sex ratios in an evergreen coniferous secondary forest with a shady forest floor. Of the 53 patches examined, 52 contained stems with flowers. Flowering stem ratios exhibited a positive relationship with available soil phosphate but a marginal negative relationship with exchangeable magnesium, whereas soil water content was associated with a female-biased flowering sex ratio. Stem density tended to be negatively related to flowering stem ratios in patches containing stems with female flowers but not males. While the results demonstrate that abundant amounts of certain nutrients and moisture in soils promote the production of flowers and/or a bias toward femaleness in patches, it is suggested that antagonistic effects of cations in the soil can inhibit the flowering of both sexes. In addition, the trade-off between sexual reproduction and clonal propagation in the females may amplify the variations in flowering in the population.

Varietal variations in temperature response for hermaphrodite flower production and fruit set in mango (Mangifera indica L)

Mango produces hermaphrodite and staminate flowers on the same inflorescence and their ratio is influenced by genetic and environmental factors. Among the various environmental factors like temperature, rainfall, relative humidity, water stress and photoperiod, temperature is one of the most important factors influencing the production of hermaphrodite flowers. Therefore it is necessary to understand the influence of temperature in a locality on the flowering behaviour of different mango cultivars to select the most suitable type. To achieve this objective, the sex ratio of flowers (hermaphrodite/staminate) was recorded in panicles that emerged during the months of January, February and March and their relationship with mean minimum temperature during floral initiation stage was assessed for two years. Wide variability in flower sex ratio was observed among the cultivars and it ranged from 0.50 to 0.58 in cultivar Arka Aruna to 5.65 to 5.98 in cultivar Langra. The optimum, mean minimum temperature for maximum sex ratio in cultivars like Alphonso, Totapuri, Arka Aruna and Amrapali was 16.6 to 16.8°C and in cultivars Langra and Kensington it was 15.5 to 15.7°C. Fruit set was increased in the month of March followed by February in most of the cultivars indicating that the fruit set is influenced by both sex ratio and the higher temperature during flowering period.

Initial Effects of Fertilization and Canopy Management on Flowering and Seed and Oil Yields of Jatropha curcas L. in Malawi

Appropriate canopy management, including planting density and pruning, and application of fertilizer may increase flowering success and seed and oil yields of Jatropha curcas L. Two field experiments were performed from 2009 to 2011 in Balaka, Malawi, to assess the effect of planting density and pruning regime and single fertilizer application (N, P, and K) on male and female flower number and seed and oil yields of J. curcas. Planting density influenced flower sex ratio and female flower number. Branch pruning treatments did not influence the flower sex ratio but reduced seed and final oil yield by 55 % in the following year. It is claimed that J. curcas can be grown on soils with low nutrient content, but this study revealed that yield was low for non-fertilized trees. We observed higher seed and oil yields at higher N application rates (up to 203 ± 42 % seed and 204 ± 45 % oil yield increase) compared with the non-fertilized control. The study suggests thatcurrently used heavy pruning practice is not recommended for J. curcas cultivation, although it needs further longer term investigation. Applying nitrogen fertilizer is effective in increasing yield.

Zink verbessert den Fruchtertrag und die Qualität von Mangos, die auf kalkreichem Boden angebaut werden

Zinc (Zn) deficiency is frequently observed in mangoes grown in calcareous soils. Inherent inability of mango to extract sufficient Zn from the soil exacerbates this situation. Therefore, mitigating effects of Zn application was investigated on flowering, fruit setting, yield and quality of mango cv. Samar Bahisht Chaunsa growing in calcareous soils. The experiment consisted of five treatments: control—no Zn, soil application of 50 and 100 g ZnSO4 per tree and foliar application of 0.5 and 1.0 % ZnSO4 solution. Zn was applied twice in the 2nd week of November, 2011 and 3rd week of March, 2012, respectively. The experiment was repeated on the same dates during the next growing season. Zn application significantly increased number of flower panicle, fruits matured panicle, leaf Zn concentrations, fruit size, peel thickness, fruit weights at harvest and after ripening and fruit yield tree, whereas it reduced malformed panicles and early fruit drop. However, flower sex ratio and fruit set remained statistically unaffected. Similarly, fruit quality in terms of total soluble solids, flesh color, aroma, flavor and overall acceptability significantly improved as compared to control. Foliar application mitigated Zn deficiency more effectively than the soil application in calcareous soils.

Effect of foliar application of GA3, ethrel and copper sulphate on flowering behaviour and sex ratio of Jatropha curcas L.

Effect of various plant growth substances viz., GA3 (25, 50,100 ppm), ethrel (1500, 2000, 2500 ppm), copper sulphate (0.1, 0.2, 0.5%) as foliar spray treatment applied during January to October was studied at 15 days intervals. The flowering behaviour and sex-expression of Jatropha curcas was investigated during in randomized block design (RBD) at the College Farm, Navsari. Looking to the results, it was noticed that GA3 50 ppm resulted in increased number of inflorescence per plant (31.25), number of flower per inflorescence (76.87), number of (male 94.75/female 4.01) flowers, flower sex ratio (24.22) in J. curcas. The Male: Female flower ratio was the lowest at 14th spray stage under majority of treatments indicating increased number of female flowers which is ultimately reflected by increased fruit and seed yield of J. curcas.

Spatial and temporal patterns of sexual dimorphism and sex ratio in Lindera benzoin L. (Lauraceae)1,2

Cipollini, M. L., (Department of Biology, Berry College, PO Box 430, Mount Berry, GA 30149), J. Culberson (2575 Oglethorpe Mountain Road, Jasper, GA 30143), D. Whigham (Plant Ecology Lab, Smithsonian Environmental Research Center, 647 Contees Wharf Road, Edgewater, MD 21037), K. Johnson (Department of Biology, Berry College, PO Box 430, Mount Berry, GA 30149), T. Knight (Environmental Studies, St. John's University, New Science Center 116, Collegeville, MN 56321) and J. O'Neill (Plant Ecology Lab, Smithsonian Environmental Research Center, 647 Contees Wharf Road, Edgewater, MD 21037). Spatial and temporal patterns of sexual dimorphism and sex ratio in Lindera benzoin L. (Lauraceae). J. Torrey Bot. Soc. 140: 280–299. 2013.—The focus of this study is spatial and temporal variation in sex ratio and sexual dimorphism in the woody dioecious shrub Lindera benzoin (spicebush, Lauraceae). This species has been shown to express female-biased flowering sex ratios in a focal study population in Maryland. Sex ratio variation and sexual dimorphism in dioecious plants has attracted the focus of many short-term, single site studies, particularly in light of Fisher's (1930) elucidation of the selective pressures favoring the production of unbiased progeny sex ratios. As informative as such studies have been, long term, multi-site studies are necessary for full evaluation of the factors leading to differential expression of sex within and among populations. Female-biased sex ratios, relatively rare among plant species, are particularly difficult to explain when many studies, including ours of L. benzoin, show females to have higher costs of reproduction and lower modular growth rates suggesting a competitive disadvantage in comparison with males. This study focuses intensively on a single population in Maryland, and is augmented by flowering censuses, and plant size and growth estimates in populations at 11 nearby sites in Maryland, and four distant sites in Pennsylvania, Virginia and West Virginia. Data were collected at most sites in the early 1990s and again in 2010, so that long-term variation in sex ratio could be explored. Results show tendencies for overall female-bias, for female bias in small size classes and male bias in large size classes, for an increase in the proportion of males within populations over time, and for sex ratios to be biased toward females in relatively recently established populations but unbiased or male-biased in older populations. Sexual dimorphism favoring males was consistent across sites, but no sexual dimorphism in herbivory by mammals or by foliage feeding insects was detected. These field observations combined with data derived from a separate but concurrent garden study suggest that early establishment of female-biased sex ratios may occur via a faster early growth rate and possible better tolerance of herbivory by females. This model further suggests that early advantages of females are followed by post-reproductive demographic changes favoring males, resulting in a tendency for sex ratios to shift toward maleness over time.

Floral display and effects of natural and artificial pollination on fruiting and seed yield of the tropical biofuel crop Jatropha curcas L.

AbstractJatropha curcas L. is a tropical tree grown on large scale as a potential biofuel seed crop. However, little information on the reproductive ecology of the species is available. This lack of knowledge makes it hard to predict yield. The higher number of male flowers than female flowers results in a very low yield. In this context, field experiments were conducted in mature (site 1) and young (site 2) plantations in Zambia and mature plantation (site 3) in Malawi to study flowering characteristics and the effect of pollination methods on the fruiting and seed yield of J. curcas. Pollination treatments were open pollination, autogamous pollination, self‐pollination, cross‐pollination and pollen supplemented open pollination. The result showed J. curcas is not only of protandrous nature as reported earlier. The male female flower sex ratio was 17 : 1, 22 : 1 and 10 : 1, respectively, for site 1 and 2 in Zambia and site 3 in Malawi. The mean flower longevity periods were 1.80 ± 0.07 days for male and 4.5 ± 0.18 days for female. Fewer fruit set and seed yield were recorded from autogamous pollination in Zambia sites. In the case of Malawi, more matured fruits resulted from autogamous pollination but the fruits contained fewer seeds. High fruit and seed yield were recorded for open pollination similar to pollen‐supplemented pollination at Zambia sites, which indicates there was no pollen limitation in these sites. In the Malawi site there was no seed yield difference between pollination treatments. The experiment showed that J. curcas can be both protandrous and protogynous and able to produce seeds through both self‐and cross‐pollination. The natural fruit set and seed yield indicates that stimulating natural pollination will improve J. curcas fruit set and seed yield.

Ecological context and metapopulation dynamics affect sex-ratio variation among dioecious plant populations.

Populations of dioecious flowering plants commonly exhibit heterogeneity in sex ratios and deviations from the equilibrium expectation of equal numbers of females and males. Yet the role of ecological and demographic factors in contributing towards biased sex ratios is currently not well understood. Species-level studies from the literature were analysed to investigate ecological correlates of among-population sex-ratio variation and metapopulation models and empirical data were used to explore the influence of demography and non-equilibrium conditions on flowering sex ratios. The survey revealed significant among-population heterogeneity in sex ratios and this was related to the degree of sampling effort. For some species, sex-ratio bias was associated with the proportion of non-reproductive individuals, with greater male bias in populations with a lower proportion of individuals that were flowering. Male-biased ratios were also found at higher altitudes and latitudes, and in more xeric sites. Simulations and empirical data indicated that clonal species exhibited greater heterogeneity in sex ratios than non-clonal species as a result of their slower approach to equilibrium. The simulations also indicated the importance of interactions between reproductive mode and founder effects, with greater departures from equilibrium in clonal populations with fewer founding individuals. The results indicate that sex-based differences in costs of reproduction and non-equilibrium conditions can each play important roles in affecting flowering sex ratios in populations of dioecious plants.

The Floral Biology of Jatropha curcas L.—A Review

Jatropha curcas L. (Euphorbiaceae) has attracted considerable recent attention as a potential horticultural crop based on the quality of its oil seed for biodiesel production, and its ability to grow in unproductive subtropical or subdesert soils. Additionally, several characteristics of the species make it a good model for a more thorough understanding of the reproductive biology of a species undergoing the domestication process. To date, there is limited information about its reproductive patterns and the genetics involved. Such information is necessary for developing efficient agronomic practices and for guiding the research needed to more fully understand the species’ reproduction processes. J. curcas has an inconsistent mating system, which presents both opportunities and challenges in developing breeding strategies and agronomic practices. Unraveling the mating system of J. curcas can increase our understanding of the evolution of reproduction systems in monoecious plants. The influences of environmental factors on flowering and floral organ development have not been reported under either field or controlled conditions. Moreover, no genetic mechanisms controlling the characteristics of the flowering (architecture, sex expression and sex ratios) have been proposed. The present review assesses and synthesizes the current knowledge of the floral biology of J. curcas. It provides a description of the species, its reproductive organs and reproductive patterns, and discussing the factors influencing them.

COMPARATIVE ANALYSES OF SEX-RATIO VARIATION IN DIOECIOUS FLOWERING PLANTS

Dioecious plant species commonly exhibit deviations from the equilibrium expectation of 1:1 sex ratio, but the mechanisms governing this variation are poorly understood. Here, we use comparative analyses of 243 species, representing 123 genera and 61 families to investigate ecological and genetic correlates of variation in the operational (flowering) sex ratio. After controlling for phylogenetic nonindependence, we examined the influence of growth form, clonality, fleshy fruits, pollen and seed dispersal vector, and the possession of sex chromosomes on sex-ratio variation. Male-biased flowering sex ratios were twice as common as female-biased ratios. Male bias was associated with long-lived growth forms (e.g., trees) and biotic seed dispersal and fleshy fruits, whereas female bias was associated with clonality, especially for herbaceous species, and abiotic pollen dispersal. Female bias occurred in species with sex chromosomes and there was some evidence for a greater degree of bias in those with heteromorphic sex chromosomes. Although the role of interactions among these correlates require further study, our results indicate that sex-based differences in costs of reproduction, pollen and seed dispersal mechanisms and sex chromosomes can each play important roles in affecting flowering sex ratios in dioecious plants.