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Mistletoe, V. coloratum, produces mature fruits of two different colors. To characterize the fruit color dimorphism and its geographic variation, we surveyed 23 populations spanning 10 latitudes in Northeast China and recorded 41 species of host plant, 2896 individual hosts, and 6641 individual fruiting mistletoes. The proportions of different color-morphs were counted in each population. In addition, we examined the variation in spectral features of the two color-morphs within and between populations, finding more red-morphs at high latitudes and more yellow-morphs at low latitudes, instead of the expected 1:1 ratio. A strong correlation was detected between the proportions of color-morphs and latitude of the population. The spectral values of the red-morph fruits were significantly correlated with the latitude of the population, while the yellow-morph showed no such correlation. We propose two unexclusive hypotheses—the food-finding strategies hypothesis and the ecological fitting hypothesis—to explain the maintenance of fruit color dimorphism and geographic variation of patterns in this species.

A phytochemical study on the rhizomes of Smilax riparia led to the isolation of 16 saponin compounds, including nine furostanol steroidal saponins (1–4, 6, 7, 10, 12, 14), six spirostanol steroidal saponins (5, 8, 9, 11, 13, 15) and one 20-carboxylic acid γ-lactone steroidal saponin (16). The structures of these compounds were identified by spectroscopic methods and comparison of their data with those reported in the literature. This is the first report of compounds 1, 4, 5, 8, 9, 11–16 from the genus Smilax . The chemotaxonomic significance of the isolated compounds has also been summarized.

The occurrence of nectarlessness flowers in nectar‐producing plants is a common and stable phenomenon in many species, but their occurrence is still not well understood. The aim of this study is to examine a question from both the plant and pollinator perspectives: why do nectar‐producing species produce some nectarless flowers within a plant? We investigate the distribution patterns of nectarless flowers in natural populations and their variation among the populations and years in a spring‐flowering self‐incompatible perennial herb plant, Corydalis ambigua Chem. & Schlecht (Fumariaceae), we observed the foraging behavior of bumblebees to nectariferous and nectarless inflorescences. We also examined the differences in reproductive success between inflorescence types and the effect of nectar production on flower production of the next flowering season. The results indicated that the frequencies of nectarless flowers varied among inflorescences, individuals, and populations and between years. Plants can revise or keep their inflorescence types or change nectar production status in the next growing season. Bumblebees visited both types with equal frequency but different foraging behavior, which resulted in lower seed production in nectarless inflorescences. However, nectarless inflorescences may save more energy and result in larger bulbs, which produce more flowers in the next flowering season. We found that although nectarless flowers resulted in lower seed set in nectarless inflorescence or individuals, they could affect bumblebees’ foraging behavior and further promote the effective output of pollen. In addition, the resource savings could enhance plant reproductive success in the next flowering season.

Varied nutrient sources can influence the plasticity of reproductive strategies in monoecious species differently. We examined the plasticity of sexual and clonal reproductive components in distinct nutrient sources in a monoecious species, Sagittaria graminea Michx. The results showed that for aboveground reproductive components, in rich-phosphorus and low-nitrogen conditions, the species produced more male flowers, whereas female flowers did not significantly increase in number compared to low-phosphorus and low-nitrogen conditions (control). In rich-nitrogen and low-phosphorus conditions, the species produced more flowers, particularly female, and more seeds, compared to the control conditions. In the rich-nitrogen and rich-phosphorus conditions, plants increased male flowers, female flowers, total flower number, synchronously, as well as seed production. For the belowground reproductive components, in the rich-phosphorus conditions, the plants produced bigger corms than in the rich-nitrogen and control conditions, which further enhanced their competitiveness against companion species. In rich-nitrogen conditions, the plants produced more medium and small corms, and relatively more and longer stolons, which were useful in expansion and invasion of more space. Furthermore, the species displayed trade-off relationships between the aboveground and belowground reproductive components in unbalanced nutrient conditions (add-N or add-P). However, in low nutrient levels (control) or in nutrient abundant (add-N + P) conditions, there were no significant trade-off relationships between the aboveground and belowground reproductive components, based on quantities.

Summary A pollination system whereby nectar resources are shared by nectar robbers, legitimate pollinators and nectar thieves, with interactions among the various types of flower visitors, was studied in a self-incompatible ephemeral perennial herb, Corydalis ambigua, in north-east China. We conducted a three-year study in nine populations, using a combination of observations, cages to exclude different combinations of flower visitors, and collars, on flowers to prevent nectar robbing. The results showed that queens of the bumblebee Bombus hypocrita sapporensis, a robberlike pollinator, had higher pollination efficiency in C. ambigua than the legitimate bee pollinators, Apis cerana and Anthophora melanognatha, which served as pollinators for inflorescences that had nectar thieves. Midges of the genus Scatopse (nectar thieves) frequently entered host flower spurs to forage for nectar and also mated there. Because nectar robbers avoided visiting nectar-thieved flowers or inflorescences, the nectar-thieved inflorescences experienced lower seed productivity. Furthermore, there was a negative relationship between the frequencies of nectar-thieved and nectar-robbed inflorescences in the nine natural populations investigated. Results of controlled experiments showed that the varied flower-visiting modes by different visitors influenced the plant's seed production. Synthesis. Although nectar theft is not uncommon, its consequences for pollination have not been well studied, particularly in the context of an interaction web. Our results demonstrate that, especially in systems that include a mix of legitimate pollinators, nectar robbers and nectar thieves, an experimental approach is required to dissect their various effects on plant fitness.

Demographic variation of gender expression among four natural populations and one cultivated in a monoecious species, Schisandra chinensis (Schisandraceae), was studied over three consecutive years in a bid to clarify its sexual system and to better understand reproductive strategies in monoecious plants. We found that gender expression was more variable in the natural populations than in the cultivated one. In the natural populations, plant size was positively correlated with flower production (total, male and female) but not with the female ratio, whereas shade intensity was negatively correlated with the female ratio. In the cultivated population, plant age was positively correlated with flower production and the female ratio within an age range. Hence, gender expression and reproductive output in Schisandra chinensis was found to be age-dependent. The female ratio varied with age; young and old plants had lower female ratios. Our study confirmed the sexual system in the species to be monoecy as opposed to dioecy, and supported the hypothesis that monoecious plants can regulate gender expression by altering quantities of pistillate and staminate flowers at the individual plant level to maximize fitness.

Floral color changes are common in Weigela and the retention of post-change flowers has been interpreted as a mechanism to increase attractiveness from a long distance and shorten pollinators’ lingering time on the inflorescence(s) of individual plants. In the present study, we investigated the temporal pattern of floral color change and time required for pollen tube growth in the shrub Weigela japonica var. sinica. Over the 4-day anthesis, the color of the corolla in this species changes from white to red and the color cue changes from yellow to purple. The duration of both the white phase and the intermediate phase is approximately 1 day and the duration of the red phase is approximately 2 days. Our studies showed that color change in Weigela japonica var. sinica is age-dependent but independent of pollinator visits and flower pollination. Post-change flowers lost most of both the male and female residual reproductive ability and retained no rewards for pollinators. It took at least 3 days for a pollen tube to grow to the ovules and achieve fertilization. Thus, retention of post-change flowers is necessary for the completion of pollen tube growth. Our results indicate that the temporal pattern of color change and time requirement for pollen tube growth are most likely related events.

The duration of sexual phases in dichogamous plants are affected by many factors. Using both experimental and observational studies, we investigated natural patterns of pollen removal and deposition, visiting frequency of pollinators, patterns of nectar secretion, and effects of pollen removal and stigmatic pollen deposition on the duration of sexual phases in a protandrous plant, Glechoma longituba. We found that visiting frequency of pollinators correlated with the nectar secretion pattern. The nectar volume during the male phase was higher than during the female phase. In the morning, the main pollinator, the bee Anthophora plumipes, mainly foraged for nectar and showed no preference for flowers in male or female phase, despite male phase flowers producing higher amounts of nectar. However, in the afternoon, they changed their behavior and foraged mainly for pollen, and then showed a preference for flowers in male phase. Furthermore, the rates of pollen removal and stigmatic pollen deposition can affect the starting time and the duration of the female phase. When pollen removal and pollination rates are low due to scarcity of pollinator services, the sexual phase can be prolonged, leading to an overlap, and thereby enhance the chance for sexual reproduction through pollinator-facilitated self-pollination. We consider the variation of sexual phases in Glechoma longituba an adaptive mechanism prepared for both cross-pollination enhancement and reproductive assurance depending on the available pollination services.

We quantified the differences in floral characters and attractiveness to flower visitors under natural conditions between the sexual types in the gynodioecious plant Glechoma longituba. We also manipulated flowers by altering corolla size or nectar volume, or by removing anthers, to examine the effect of these primary and secondary attractants (i.e. rewards and advertisements) on attractiveness. A change in corolla size and shape reduced visiting frequency and pollen load. Removal of anthers did not affect visiting rates, but significantly reduced pollination rates and stigmatic pollen load. A decrease in the nectar volume of a flower was associated with a reduction in handling time and pollen loads on stigmas. These results show that corolla size is an important advertisement to pollinators (particularly at greater distance), which associate hermaphrodite flowers with a larger corolla and a larger volume of nectar than female flowers. We found that artificial changes in population structure affected the behavior of pollinators as well as the pollination rates of flowers. We suggest that the pattern of distribution of hermaphrodite and female clones in a population may serve to avoid pollen limitation in a female clone or patch. This effect may ensure female reproductive success and allow for the maintenance of female individuals in natural populations of this gynodioecious plant.

The relationship between plant and pollinator is considered as a mutualism because plant benefits from the pollinator's transport of male gametes. Nectar robbers are frequently described as cheaters in the plant-pollinator mutualism, because it is assumed that they obtain a reward (nectar) without providing a service (pollination). Nectar robbers are birds, insects, or flower visitors that remove nectar from flowers through a hole pierced or bitten in the corolla. Nectar robbing represents a complex relationship between animals and plants. Whether plants benefit from the relationship is always the controversial part in earlier studies. This paper is to review the recent literatures on nectar robbing and attempt to acquire an expanded understanding of the ecological and evolutionary roles that robbers play. Understanding the effects of nectar robbers on the plants that they visited and other flower visitors is especially important when one considers the high rates of robbing that a plant population may experience and the high percentage of all flower visitors that nectar robbers make to some species.There are two standpoints in explaining why animals forage on flowers and steal nectar in an illegitimate behavior. One is that animals can only get food in illegitimate's way because of the mismatch of the morphologies of animals' mouthparts and floral structure. The other point of view argues that nectar robbing is a relatively more efficient, thus more energy-saving way for animals to get nectar from flowers. This is probably associated with the difficulty of changing attitudes that have been held for a long time. In the case of positive effect, the bodies of nectar robbers frequently touch the sex organs of plants during their visiting to the flowers and causing pollination. The neutral effect, nectar robbers' behavior may destruct the corollas of flowers, but they neither touch the sex organs nor destroy the ovules. Their behavior don't affect the fruit sets or seed sets of the hosting plant. Beside the direct impacts on plants, nectar robbers may also have an indirect effect on the behavior of the legitimate pollinators. In some circumstances, the change in pollinator behavior could result in improved reproductive fitness of plants through increased pollen flow and out-crossing.

Nectar robbing not only affects the reproductive fitness of the plant but it may also potentially affect the pollination dynamics of the associated coflowering individuals. In this study, we established that the nectar robber Xylocopa sinensis robs nectar only from the hermaphrodite ramets of the gynodioecious plant Glechoma longituba but not from the female ramets. In populations with high rates of nectar robbing, this results in hermaphrodite ramets having reduced seed set whereas the female ramets have a slightly increased seed set. We hypothesize that selective nectar robbing confers an advantage to female individuals and thus ensures their maintenance in gynodioecious populations. Results of controlled experiments indicated that the reduction in the amounts of nectar available occasioned by nectar robbing resulted in some legitimate pollinators switching to visiting flowers on female rather than hermaphrodite ramets. This resulted in lower pollination rates and seed set for hermaphrodites and higher pollination rates and seed set for females. This study presents a previously unreported mechanism causing female advantage in gynodioecious plants.