Pollination has been recognized to be an important ecological process to maintain and promote biodiversity on earth. The order Hymenoptera, especially the superfamily Apoidea, is one of the most abundant and diverse groups among natural pollinators. However, studies on the ecological functions of wild bee pollinators have been underappreciated in China. More professional taxonomists are urgently needed to sur-vey fauna, to provide accurate identifications and to do comprehensive studies. Our understanding of nesting biology or pollination biology is not comprehensive for most wild bees. On the other side, much more atten-tion should be paid to the associations between bees and plants for their application to various projects on pollination biology, biodiversity or conservation biology in the future. We review current research on the status of wild bees, and we anticipate further applications to practices in agriculture and forestry with infor-mation from taxonomy, nesting biology and pollination biology of wild bees.

Complete understanding of floral function requires the recognition of floral traits at two aspects: floral design and floral display. Floral display, the fundamental unit of plant mating, refers to the number, type and arrangement of the open flowers on the plant in a certain period. Interactions between the flowers on a plant could influence pollinator behaviors on the plant and consequently may govern the mating outcomes. Pollinators prefer large floral displays, which often receive more visitations than smaller displays and thus could facilitate geitonogamous pollination. However, visitations for each flower do not increase with display size directly, suggesting that the variation of display size would balance the benefit of attractiveness against the cost of self-pollination. Flower morphs, such as unisexual or perfect flowers on one plant, may have dif-ferent gender function varying with pollinator preference and when or how much reward is available. Flow-ers on one plant also vary on size, color and reward to affect pollinator’s visitation behavior and minimize the potential self-pollination. Floral display often contains a three-dimensional floral arrangement that could in-fluence pollinator attraction and forage energy at a large scale, and is dynamic in response to the complex pollination and physical environments. Here we briefly review the progress of studies on floral display. It is clear that further studies on the interactions between floral traits and various pollination environments would provide insights into ecological functions of diverse floral displays in angiosperms.

The majority of flowering plants and crops rely in whole or part on animals for pollination. The mutualism between plants and pollinators has attracted ecologists and evolutionists to use this type of interspecific interaction as a model system to study species adaptation and diversification since Charles Darwin. Recent debate on the nature of pollination systems call for studies of this interaction at different levels, ranging from single species to entire communities in a given area. At the species level, detailed studies suggest that floral traits are under selection from mutualists and antagonists as well as the physical environment. In contrast, studies at community-level are rare, but recent analyses indicate considerable spatial and temporal variation in both generalized and specialized pollination systems. This special issue of Biodiversity Science focuses on plant-pollinator interaction, presenting current research status in this area from China. Papers include floral traits and pollinator behaviors addressed by phenotypic manipulation, estimates of pollen removal and receipt, anatomy of flowers, histochemistry analysis and spatial and temporal comparison. The taxa being investigated include wild orchid and cultivated legume, endemic, endangered and invasive species with diverse sexual systems. These thirteen experimental studies and three reviews show the development of pollination biology in China and expose how to facilitate our understanding of the critical ecological proc-esses underlying interspecific interaction in both natural and agricultural ecosystems.

Foraging behavior of pollinating insects can directly influence plant–pollinator interactions in many aspects, thus studies on pollinator behavior are important for understanding plant diversity and ecological processes of plant reproduction. In this paper, we describe the characteristics of major pollinating insects and discuss the methods for studying foraging behavior of pollinating insects and factors potentially influencing pollinator behaviors. We also suggest some practical methods for studying the roles of nocturnal pollinators and how to conduct studies of insect foraging behaviors at community level. The purpose of this introduction is to provide some useful information for future studies on this multidisciplinary research in China, particularly for botanists and entomologists.

The orchid family is renowned for its enormous diversity of pollination mechanisms and unusually high occurrence of non-rewarding flowers compared to other plant families. We investigated the pollination biol-ogy of Cymbidium lancifolium during 2005 and 2006 in the Yachang Nature Reserve, Guangxi Province, SW China. Our observations showed that Apis cerana cerana (Hymenopterous, Apidae) was the only pollinator. The bee directly landed on the mid-lobe, then adjusted its direction and entered into the flower. When it found no rewards in the flower, it would exit from the flower with the hind legs forcibly grasping the mid-lobe. The pollinaria together with the anther cap adhered to the thorax by the viscidium during the re-treating process of the bees. The pollinator stayed for 8–71 s in the flower with an average of 18.3 s (N = 11). It is likely that C. lancifolium attracted the bee by the purplish chestnut spots on the labellum (false nectar guides) exploiting the foraging preference of bees. The anther cap that remained on the back of the pollinator blocked the pollinaria from being received by the subsequently visited flower. The height of the anther cap (0.154 ± 0.032 cm) (N = 10) together with thorax of the pollinator (2005: 0.37 ± 0.03 cm (N = 10), 2006: 0.35 ± 0.04 cm (N = 7)) was higher than the entrance of the flower (0.29 ± 0.04 cm) (N = 21), suggesting a possi-bility of anther cap retention for geitonogamy. The reproductive success in the population was respectively 21.13% and 21.28% in 2005 and 2006. Breeding experiments showed that C. lancifolium was self-compatible and there was no significant difference in reproductive success between self-pollination and cross-pollination. There was neither apomixes nor spontaneous autogamy. The pollination success of this species was depend-ent on pollinators. The viability of seed by TTC was estimated as 85.78% (N = 11), and it was not considered to be the key limiting factor for seed germination. Therefore, it is suggested that other factors, such as the density of the pollinators and their pollination frequency, influence the fruit set and maintenance of the popu-lation of C. lancifolium.

Primula merrilliana, a rare and endangered National Grade Ⅲ protected plant, is endemic to Anhui Province, China. We studied its reproductive characteristics from the aspects of phenology, breeding system structure and pollination. Our observations showed that: (1) P. merrilliana is typically distylous in both mor-phology and function, and it is a biennial plant that grows from September in the first year and lasts until late June or early July of the next year. In addition, the long-styled plants tend to flower 3 to 5 days earlier than the short-styled morphs in each population; (2) The pantoporate pollen of P. merrilliana shows that the spe-cies has vital taxonomical and evolutionary significance in Primula. The short-styled pollen diameter is 1.78 times as wide as the long-styled, but the pollen production of a short-styled flower is less than that of a long-styled flower; (3) The long-styled pistil is about 1.64 times as long as that of the short-styled morph with shorter and more frequent papillae; (4) The pollen-ovule ratio (P/O) is different in the three studied populations, and we noted larger variation in pollen than ovule production, which may be related to habitats; (5) P. merrilliana is an outcrossing plant pollinated by thrips, and the seed-set of legitimate pollination is higher than that of illegitimate; and (6) The seed morphology of P. merrilliana usually appears like a non-equilateral heptahedron, a few seeds resembles an irregular polyhedron, but there is no obvious difference between the two morphs, the long-styled and the short-styled. Based on this study, biased morph frequencies in small populations of P. merrilliana, destruction of habitats and disappearance of accompanying species are possibly the main reasons for the endangerment of this species.

During May to July, 2006 and April to May, 2007, we studied pollination biology in Ipomoea cairica, an invasive weed in Guangdong Province, China. Ipomoea cairica is a perennial creeping or climbing herbaceous vine, blooming all year round in Guangdong. The flowers gathered in cymes, with a purple or bluish purple bell-formed corolla. The petals unfolded at about 4:30–5:20 and closed at 17:40, lasting for about 12 hours. The proximity of the stigma and anthers during flowering period facilitated the transfer of self-pollen. The mean volume of nectar per flower was 5.82 ± 2.47 μL (n = 10), with a sugar concentration of 41.03 ± 6.52% and an amino acid concentration of ca. 0.042 mg/mL. During anthesis, both pollen viability and stigma receptivity remained at a high level (>90%). The mean P/O ratio was 4,778.18 ± 264.58 (n = 10). Carpenter Bees (Xylocopa sp.) were considered as effective pollinators, while flies and butterflies were occa-sional visitors. Ipomoea cairica is self-incompatible as determined by an absence of fruit set in the flowers following controlled hand self-pollination, producing fruits and viable seeds only after cross-pollination.

Self-incompatibility occurs widely in the Solanaceae, but a few species in this family, or a few intraspecific populations or a few individuals within the populations are highly self-compatible and their breeding systems have evolved from outcrossing to selfing. We studied pollination biology of Anisodus tanguticus from this family, a perennial endemic to the Qinghai-Tibetan Plateau. This species flowers in the early summer and probably suffers from the serious limitations of the outcrossing pollinator. We aimed to test whether the breeding systems of a few individuals in this species have shifted from outcrossing to selfing. Our experiments and observations were conducted in two populations with different altitudes. Most flowers of this species were incompletely protogynous, and the mean distance between the stigma and anthers decreased gradually with floral longevity. Both stigma and anthers did not come into touch when the corolla wilted in most of the monitored flowers and such herkogamy favours outcrossing. However, the complete contact of stigma and anthers in 4.9% of the measured flowers suggested potential occurrence of “autonomous selfing” in these flowers. Most of the examined individuals in both populations are self-incompatible and have to depend on insects for pollination. However, a few of them were found to be self-compatible. Flies were the effective outcrossing pollinators in the high altitude population and “autonomous selfing” was detected in a few individuals of this population. In contrast, the effective outcrossing pollinators were rarely observed in the low altitude population and the dominant visitors or pollinators, ants in this population, transferred pollen within the single flower, which finally resulted in “facilitated selfing”. Pollination limita-tions were obvious in both populations due to the lack of enough outcrossing pollinators. Two different self-ing mechanisms, uncovered here, may provide a partial compensation for the natural reproduction of this al-pine species in the arid alpine habitats when flowering at the early summer.

Flexistyly is a unique sexual dimorphic system found in Amomum and Alpinia species of the ginger family (Zingiberaceae). The populations of flexistylous species have two phenotypes, named an anaflexistylous morph and a cataflexistylous morph, and all individuals of both morphs separate their male and female functions spatio-temporally. We conducted manipulated pollinations and pollen tube growth experiments on Alpinia blepharocalyx and A. galanga to detect the manner of separation of male and female functions within the individual and its adaptive significance. The results showed that the outcrossing rates of manipulated and natural pollination in the cata-morph did not differ significantly (P>0.05). However, the number of seeds per fruit of manipulated cata-morphs was significantly lower (P<0.01) than that of control individuals, perhaps due to the inbreeding depression caused by ovule discounting. Pollen tube growth experiments showed that, when stigma were located at the receptive position (ana-morph in AM, cata-morph in PM), stigma provided appropriate conditions (had stigmatic secretion) for pollen grain germination, and pollen tubes penetrated into the style within 2 hours after pollination, regardless treatment of selfing or outcrossing. However, when stigma were beyond the anther (ana-morph in PM, cata-morph in AM, without stigmatic secretion), it usually took 6–10 hours for pollen germination and pollen tube penetration. Pollen tubes, however, could reach the ovary within 24 hours under both treatments. Hand-pollination also showed that pollen grains of anaflexistylous flowers have matured before the dehiscence of pollen sacs. Our research suggests that flexistyly is a floral dimorphism comprising reciprocal mobile herkogamy and heterodichog-amy. Heterodichogamy encourages outcrossing, meanwhile reciprocal curvatures of stigmas play a role of reducing interference between male and female functions.

Interaction between animal-pollinated plants and their pollinators is thought to be an important selecting force shaping the evolution of flowers. Successful pollination of a plant relies on its attractiveness to pollinators and the ability of the pollinators to deposit enough compatible pollen on the flower’s stigma. To assess the attractiveness, we manipulated the flower of Aconitum kusnezoffii by removing the sepals and pet-als, respectively. We then evaluated the mating system based on pollinator behavior and flower biology of A. kusnezoffii. The bumblebee, Bombus ignites, was the effective pollinator of A. kusnezoffii. Bumblebee be-havior differed on the manipulated flowers. The visiting frequency was significantly reduced by se-pal-removal treatment, but remained unchanged by nectar-removal treatment. Bumblebees were attracted by the flower exterior morphology formed by five sepals, not by the nectary formed by the two petals. The two lower sepals provided a landing platform, and the uppermost sepal functioned as a nectar guide, ensuring bumblebee find the nectar precisely and rapidly. The two lateral sepals restricted the direction in which a bumblebee can enter the flower, ensuring pollination efficiency in zygomorphic flowers. Nectar was the main reward for bumblebees, with a sugar concentration of 39.23% and histidine concentration of 0.25 μg/μL. The flower of A. kusnezoffii was large, protandrous and herkogamous, suggesting an outcrossing mating system based on the outcrossing index. In Aconitum inflorescences the oldest flowers were functionally female at the bottom of acropetal racemes, while younger flowers were functionally male at the upper positions. Bombus ignites generally flew from a younger functionally male flower near the top of an A. kusnezoffii inflorescence to an older functionally female flower near the bottom of another inflorescence, and then moved progres-sively upward. This behavior promoted the outcrossing of A. kusnezoffii. Aconitum kusnezoffii flowers were strongly protandrous, with the male phase lasting 2–4 days, during which the anthers gradually dehisced. Aconitum packaged pollen within each flower as individual anthers dehisced over a protracted period. Such pollen packaging necessarily limited pollen removal during single visits and increased male fitness by pro-moting pollen dispersal.

In order to donate pollen to recipient stigmas efficiently, animal-pollinated plants have evolved a variety of floral characteristics. Pollen presentation schedule is one of them. Plants can control the pace of pollen presentation and distribute pollen among pollinators by either packaging or dispensing mechanisms. Pollen presentation theory (PPT) predicts that gradual pollen presentation should be favored when pollinators are abundant or inefficient at delivering the pollen they remove; while synchronous pollen presentation should be favored when pollinators are infrequent or efficient at delivering the pollen they remove. Here, we present a review of recent advances in this field, with an emphasis on: (1) floral mechanisms restricting pollen removal; (2) pollen presentation theory; and (3) evolutionary advantages of pollen presentation schedules. Current research focuses on the adaptability of pollen presentation schedule to the pollinating animals, while environmental factors also work on the schedule. The PPT model cannot fully predict the pollen presentation temporal schedule of plants distributed in special environments, thus further combined studies and analyses are needed regarding floral syndromes, pollination systems, mating systems and environment factors in suit-able groups. These results will help us have a better understanding of the adaptive advantages of pollen pres-entation schedules.

Hedysarum laeve (Fabaceae) is an important legume for plant ecosystem restoration and reconstruction in Mu Us Sandland, Inner Mongolia. Fruit set is greatly enhanced when pollinators are available in the H. laeve system, since fruit set is stimulated less by spontaneous autogamy. This species is pollinated mainly by wild bees, but there is insufficient information to determine the overall effectiveness or importance of the pollinators. We investigated the composition of bee pollinator species of H. laeve and the pollination efficiency of the dominant ones. The species and numbers of pollinators of H. laeve were investigated in four 2 m×2 m plots in Mu Us Sandland during 2004–2006. We observed visitation frequency of the main pollinators and measured their pollen removal ratio from anthers after a single visit to virgin flowers, pollen deposition on stigmas by a single visit to virgin flowers, and the duration of each visit. The results showed that three bees Anthophora albifronella, Megachile maritima and Bombus sporsdicus were major pollinators, of which A. albifronella was dominant in number and visitation frequency. A. albifronella removed less pollen than M. maritima and B. sporsdicus, but the three bee species deposited similar amounts of pollen on stigmas. We suggest that A. albifronella was the most efficient pollinator for H. laeve according to comparison among the three bees of the amount of pollen removal, the pollen deposition on stigmas, and visitation frequency.

Mutualism is a relationship between individuals of different species that benefits all the partners. However, this interaction may also be described as mutual exploitation. The “host sanctions effect” predicts that the hosts punish partners that cheat by receiving benefits without paying for them. Fig trees (Ficus) and their fig-pollinating wasps (Agaonidae) constitute a mutualistic system with a mainly one-to-one relationship. In order to test if there exists the “host sanctions effect”, we carried out a study at Xishuangbanna Tropical Botanical Garden, Yunnan Province on the monoecious fig tree Ficus benjamina, which is actively pollinated by Eupristina koningsbergeri. We produced two groups of pollinating wasps, either carrying pollen or not, and introduced one or two foundress wasps from each group into single figs. Figs entered by no wasps aborted rapidly, but almost all figs entered by wasps completed their development normally, except a few entered by a single pollen-free wasp. However, pollen-loaded foundresses produced significantly larger broods than foundresses without pollen. This effect was particularly marked in figs containing two foundresses. Our results show that active pollination is not essential for the reproduction of the pollinator, but does improve its reproductive success. This suggests that a sanctions effect is operating.

Insect visitation was preliminarily monitored in some typical herbaceous plant communities at different altitudes (1,000–2,600 m) in the Shennongjia Mountains, Hubei Province, China. In the nine quadrats studied, insects in eleven families of Hymenoptera, Lepidoptera and Diptera were observed to be floral visitors. The taxa of insect visitors were visibly associated with the community composition. Observing the behavior of floral visitors, we found that the total visitation frequency and the frequency of visits of each kind of insect both differed in communities with different plant species, and that more insect species ap-peared in communities with more plant species in bloom. Visitation frequencies to some plant species were significantly different when they occurred in different communities. For example, no insects were observed to visit Rumex acetosa flowers, with an indistinctive perianth, in some communities, but high visitation fre-quencies were observed in others. Geranium henryi, featuring an obvious perianth, was visited by insects in every community. On the other hand, some plants, such as Vicia cracca, were always visited by insects, but the taxa of visitors were different in each community. Our results suggest that different plants contributed to various roles in attracting pollinators within communities, and one should consider the community back-ground of the plant populations in studies of plant–pollinator interactions.

The nutritive reserves in angiosperm pollen grains and the pollen and ovule numbers of single flowers are considered to be correlated with the pollinating vectors. In this paper, we studied the relationships between pollen histochemistry, pollen grain number, ovule number and pollinators in Phyllanthaceae. Hymenoptera- and Diptera-pollinated species tend to have starchless, lipid-rich pollen while most Lepidopteran-pollinated species have starchy pollen grains. No correlation was found between pollinator-types and pollen number of single flowers. Flowers of fly-pollinated species have much fewer ovules than flowers of moth-pollinated species. It is suggested that the decrease in ovule number may be an adaptation to the pollinating flies, which have relatively poorer pollen-transferring ability and which transfer pollen less precisely in comparison with other pollinating insects such as moths or butterflies. Pollen grains in single flowers of shrub species were found to be almost ten times as many as that of herbs, while the tree species also have higher pollen grain numbers than congeneric shrub species. This may be due to the different flower size in plants with different life forms. Significant differences were found in the pollen ornamentation patterns under SEM between fly-pollinated and moth-pollinated species.

Natural hybridization mediated by pollen flow has been considered as an important factor to drive speciation in Rhododendron, one of the largest genera within alpine plants. The diversity of Rhododendron species is centered in southwestern China, yet the potential role of interspecific pollination in natural hybridization has not been empirically examined in this area. Here we investigated the flowering period and floral visitors, and conducted a series of pollination experiments to examine breeding systems and hybrid compatibility within four Rhododendron which are frequently sympatric in Yunnan Province. Rhododendron delavayi and R. decorum are clearly distinct by their morphological traits, but the putative hybrids R. agastum and R. irroratum are morphologically between the other two species. We observed that R. delavayi flowered from the beginning of March to the end of May, R. agastum and R. irroratum flowered from the beginning of March to the beginning of April, and after their flowering periods ended, R. decorum began to flower until the end of May. The anthesis of single flowers of the four Rhododendron species was almost one week. The floral visitors belong to the Hymenoptera and Diptera Orders, and Apis cerana cerana visited all of the four Rhododendron species. We found that R. delavayi, R. agastum and R. decorum are self-incompatible, but not R. irroratum. No breeding barrier between any of the four species was detected by artificial pollination, and the hybrid seeds were fertile. The hybrids between four species showed equivalent fitness to their par-ents. We suggest that the role of potential interspecific pollination is essential to hybrid speciation and evolu-tion of Rhododendron species.

The floral nectaries of three species of Musaceae s. s. representing the genera Musa, Ensete and Musella were comparatively investigated. Our observations revealed that nectaries of these three genera belonged to the interlocular septal type. In female flowers, nectaries were limited to the upper part of the ovaries above the locules, while in male flowers (with aborted ovaries) nectaries entirely occupied the aborted ovaries. A transection of nectary ducts suggested a complex and highly proliferated labyrinthine structure. The three species shared a few common features in the palisade-like epithelial cells, vascular supplies, and nectary openings. However, they showed some differences in longitudinal section and transectinal outline. The nectaries of Ensete glaucum had the highest starch content, and those of Musa basjoo and E. glaucum had fibrillar material presented in nectar ducts. Pollination syndromes among the three species showed high diversity, while inflorescence and flower characters (such as pendant or erect inflorescences, bract color, nectar volume and production over time, etc.) and pollination patterns were highly correlated. There were no strong correlations between nectary structures and pollinator behavior, although gelatinous or watery nectar was associated with the foraging preference of pollinators.