Reproductive strategies of Strobilanthes kunthianus, an endemic, semelparous species in southern Western Ghats, India

Strobilanthes kunthianus (Acanthaceae) is a semelparous species with synchronized flowering and mast seeding once in 12 years. As semelparous plants have only one chance to reproduce, they are expected to develop effective strategies to prevent reproductive failure. The reproductive strategies of S. kunthianus were investigated by studying the floral traits, pollination biology, and breeding system that are critical for reproductive success. The species exhibits a series of floral traits: (1) gregarious flowering attracts a large number of Apis cerana indica , the major pollinator; (2) the stigma is sensitive to touch by the pollinator; in fresh flowers, the receptive surface faces the entry path of the incoming bee, facilitating pollen deposition; as an immediate response, the stigma curves backwards moving the receptive surface away from the path of the exiting bee, thus preventing autogamy and interference in pollen transfer; (3) flowers remain fresh for 2 days with receptive stigma and nectar and pollen reward. These traits render the species 100% pollination efficient to ensure a high seed set. As the species is self-compatible, the prevailing high degree of geitonogamous pollinations does not interfere with fruit set. The evolution of the adaptive floral traits has facilitated mast seeding in the species.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 155–163.     

Reproductive biology in Anagyris foetida L. (Leguminosae), an autumn–winter flowering and ornithophilous Mediterranean shrub

As most plants of the Mediterranean region bloom in spring, there have been few studies of the reproductive biology of species with autumn–winter flowering. In this study, we investigate the breeding system of Anagyris foetida , one of the few shrubs that blooms at this time. The floral, phenological, and reproductive aspects of two populations of this Mediterranean legume from south-west Spain were studied via field and laboratory experiments. The variability of fruit and seeds was studied in another 12 Iberian populations with respect to certain meteorological parameters (temperature and rainfall). Anagyris foetida shows cauliflory, marked floral longevity, and adichogamy. The peak of flowering is in January–February. It is self-compatible, with no clear advantage of cross- over self-pollination, and with virtually no autonomous self-pollination. This is because the stigma, like some other legumes, prevents the germination of pollen if its surface is not ruptured by pollinators. The number of seeds per fruit under natural pollination was positively correlated with the total rainfall during the fruiting period (from January to May), and significantly influenced the percentage of fruit weight represented by the pericarp, in the sense that the smaller the number of viable seeds in the fruit, the greater the percentage of pericarp weight.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 519–532.     

Variation in native pollinators in the absence of honeybees: implications for reproductive success of an Australian generalist-pollinated herb Trachymene incisa (Apiaceae)

Most plants are generalist in terms of pollination, with the potential for significant spatial and temporal variation in their pollinators. Few studies have investigated how variable pollinators are in a generalist pollination system or how this variation affects plant reproduction. We investigated the degree of variation in pollinators and resulting reproductive success among populations of a widespread generalist-pollinated herb, Trachymene incisa (Apiaceae). The European honeybee was unexpectedly absent from the pollinator assemblages, providing the unique opportunity to study the native Australian pollinators. Insect visitation rates and the taxonomic composition of the pollinator assemblage varied significantly across populations, indicating that populations of T. incisa are not equally serviced and are not equally generalist. This highlights that sampling one population would not characterize the extent of species generalization. There was no positive correlation between insect visitation rate and reproductive success, with the Agnes Banks population receiving the highest visitation rate but producing the lowest reproductive output, and the Myall Lakes population receiving the lowest visitation rate and producing the highest seedling emergence. This study shows that variation in pollinators can have measurable effects on populations of generalist-pollinated plants, therefore there is potential for large-scale change in all plant–pollinator interactions.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 479–490.     

Female reproductive success in gynodioecious Thymus vulgaris: pollen versus nutrient limitation and pollinator foraging behaviour

Gynodioecy is a dimorphic breeding system in which female individuals coexist with hermaphroditic individuals in the same population. Females only contribute to the next generation via ovules, and many studies have shown that they are usually less attractive than hermaphrodites to pollinators. Several mechanisms have been proposed to explain how females manage to persist in populations despite these disadvantages. The ‘resource reallocation hypothesis’ (RRH) states that females channel resources not invested in pollen production and floral advertisement towards the production of more and/or larger seeds. We investigated pollination patterns and tested the RRH in a population of Thymus vulgaris. We measured flower display, flower size, nectar production, visitation rates, pollinator constancy and flower lifespan in the two morphs. In addition, we measured experimentally the effects of pollen and resource addition on female reproductive success (fruit set, seed set, seed weight) of the two morphs. Despite lower investment in floral advertisement, female individuals were no less attractive to pollinators than hermaphrodites on a per flower basis. Other measures of pollinator behaviour (number of flowers visited per plant, morph preference and morph constancy) also showed that pollinators did not discriminate against female flowers. In addition, stigma receptivity was longer in female flowers. Accordingly, and contrary to most studies on gynodioecious species, reproductive success of females was not pollen limited. Instead, seed production was pollen limited in hermaphrodites, suggesting low levels of cross‐pollination in hermaphrodites. Seed production was resource limited in hermaphrodites, but not in females, thus providing support for the RRH. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 175 , 395–408.     

Pollination of the lady's slipper Cypripedium henryi Rolfe (Orchidaceae)

The pollination ecology of Cypripedium henryi Rolfe, a slipper orchid endemic to west China, was investigated, and its floral shape, size, colour, and scent were analysed. Examination of the breeding system suggests that the flowers are self-compatible, but need pollen vectors for successful reproduction. The flower is rewardless; over 15 insects belonging to Araneida, Hymenoptera, Diptera, Lepidoptera, and Coleoptera were recorded as flower visitors, but most only alighted or rested on the flower. In the total 32 h of observations over 2 years, female Lasioglossum bees were found to be the most frequent visitors and the only pollinators. They showed a high visitation frequency and, surprisingly, re-visited the same flowers frequently. Cypripedium henryi probably attracts pollinators visiting the flowers through general food deception (odour components, colour, false nectar guides), as well as special structures (slippery labellum, slippery staminode). Although three Lasioglossum species visited the flowers, only L. sauterum Fan et Ebmer was found with pollen. Lasioglossum flavohirtum Ebmer was large and climbed out from the entrance. Morphologically, L. sichuanense Fan et Ebmer could be considered as a potential pollinator, but the collected specimens were found to have no pollen of C. henryi on their bodies. It was speculated that the particular floral scent of C. henryi discouraged the entrance of L. sichuanense bees. Lasioglossum sauterum was matched morphologically to the flower, but not all of the visitations resulted in effective pollinations, as some flowers of C. henryi were frequently re-visited and the pollen mass had been taken away by bees on previous visitations. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 491–499.     

Reproductive ecology of the endemic Lecocarpus pinnatifidus (Asteraceae) in an isolated population in the Galápagos Islands

Lecocarpus pinnatifidus is an endemic member of the Asteraceae occurring on only one island in the Galápagos archipelago. The capitula are large with female ray florets and male disc florets. They are self-compatible but this study suggests fruit set is pollen limited. Visits from Xylocopa darwini and other larger insect pollinators are rare, and small insects seem to be the main pollinators. Small insects carry few pollen grains and most likely mediate self-pollinations. Self-compatibility and seed set after selfing are the most common reproductive strategy in the Galápagos Islands and L. pinnatifidus seemingly fits well into this group.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 171–180.     

Breeding system and bird pollination of Camellia pubipetala,a narrowly endemic plant from karst regions of south China

Camellia pubipetala is an endemic and endangered species with small and isolated populations occurring only in karst regions in Guangxi of south China. To understand the reproductive biology of C. pubipetala and its possible influences upon its endangered status, its breeding system and pollination ecology were studied in the Longhushan (LHS) and Longzhao (LZ) populations of this species. The flowering duration of the C. pubipetala populations spanned from late January to early April and anthesis of a single flower usually lasted 5–7 days. This species is homogamous, and the pollen and stigma are viable throughout anthesis. Each bagged flower could secrete 141.5 μL of nectar at a sugar concentration of 25.0% during anthesis. The observed high pollen/ovule ratio, and the results of hand-pollination experiments indicated that this species obligately outcrosses. Open pollination resulted in a significantly decreased fruit set (6.7%) and seed set (38.9%) compared to supplementary pollination treatment (23.3% and 64.7%, respectively), which is indicative of a pollen limitation in the process of pollination. The primary pollinator of C. pubipetala is the sunbird Aethopyga christinae and its visiting frequency is quite low, whereas the honeybee Apis cerana is only an occasional pollinator in wild populations. Low reproductive rates in C. pubipetala were found to be a consequence of few species of pollinators and their low visiting frequency. Pollen limitation may be a crucial factor that contributes to the endangered nature of this species. Artificial pollination and the release of pollinators are effective ways to increase the fruit and seed yield of this species.     

Pollinator‐mediated phenotypic selection does not always modulate flower size and number in the large‐flowered Mediterranean shrub Cistus ladanifer (Cistaceae)

Flower size and number usually evolve under pollinator‐mediated selection. However, hot, dry environments can also modulate display, counteracting pollinator attraction. Increased pollen deposition on larger flower displays may not involve higher female fitness. Consequently, stressful conditions may constrain flower size, favouring smaller‐sized flowers. The large‐flowered, self‐incompatible Mediterranean shrub Cistus ladanifer was used to test that: (1) this species suffers pollen limitation; (2) pollinators are spatially–temporally variable and differentially visit plants with more/larger flowers; (3) increased visits enhance reproduction under pollen limitation; (4) stressful conditions reduce female fitness of larger displays; and (5) phenotypic selection on floral display is not just pollinator‐mediated. We evaluated pollen limitation, related floral display to pollinator visits and fruit and seed production and estimated phenotypic selection. Flower size was 7.2–10.5 cm and varied spatially–temporally. Visitation rates (total visits/50 min) ranged from 0.26 to 0.43 and increased with flower size. Fruit set averaged 80% and seed number averaged 855, but only fruit set varied between populations and years. Selection towards larger flowers was detected under conditions of pollen limitation. Otherwise, we detected stabilizing selection on flower size and negative selection on flower number. Our results suggest that selection on floral display is not only pollinator‐dependent through female fitness in C. ladanifer. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 176 , 540–555.     

The effect of flower position on male and female reproductive success in a deceptively pollinated tropical orchid

In many plants, including orchids, differential fruit set along the inflorescence has been attributed to pollinator behaviour. For instance, the pollinator, moving up the inflorescence, becomes satiated with the resources and leaves before visiting the upper flowers. Consequently, the pollinators do not visit flowers as frequently higher up the inflorescence. Alternatively, flower size may vary along the inflorescence, making pollination ineffective as flowers decrease in size. I tested for the presence of differential pollination along the inflorescence in a pollinator-limited tropical epiphyte, Lepanthes rupestris Stimson, and determined the likely cause of the observed pattern. As this species has inflorescences with sequential flowering, pollinator behaviour, moving up the inflorescence as in synchronous multiflowering inflorescences, can be discounted as an explanation for differential fruit set. Fruit set is shown to be more frequent at the base of the inflorescence, but male reproductive success through pollinarium removal is basically independent of flower position. Moreover, cross-pollination by hand at variable flower positions along the inflorescence results in equal fruit set, suggesting that resources are not limiting and cannot explain the cause of differential fruit production along the inflorescence in natural populations. Furthermore, flower size is shown to diminish along the inflorescence, suggesting that the pollinator(s) may be ineffective at depositing the pollinarium in the smaller higher flowers. Consequently, pollinator behaviour and its interaction with flower size, and not resource limitation, is likely to be the main cause of differential fruit set along the inflorescence in L. rupestris .  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 151 , 405–410.     

Reproductive biology of the invasive exotic shrub, Rhododendron ponticum L. (Ericaceae)

The reproductive biology of an exotic species will affect its ability to become naturalized and invasive in non-native habitats. Rhododendron ponticum is an ecologically damaging exotic weed in the British Isles, which spreads predominantly by seed. I investigated how inbreeding and outcrossing affect seed production and germination in a wild population of this species in Ireland. Experimental manipulations revealed low fruit and seed set when insects were excluded from flowers, suggesting that this species has limited capability for spontaneous autogamy. Hand-pollination treatments showed that, although flowers are self-compatible (with self and same plant pollen), higher levels of seed set occur following outcrossing (xenogamy). There was no significant difference in rate of germination of seeds from inbred or outcrossed treatments. The addition of xenogamous pollen to open flowers did not increase fruit or seed set, suggesting that flowers in this population are not pollen limited: native generalist pollinators, mainly bumblebees ( Bombus spp.), are providing an adequate pollinator service. This work demonstrates that outcrossing increases seed set and pollinators are required to facilitate this. Hence, generalist native pollinators can promote invasion by exotic plants. Native pollinators can clearly play an important part in alien species invasion.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 373–381.     

Philodendron adamantinum (Araceae) lures its single cyclocephaline scarab pollinator with specific dominant floral scent volatiles

Cyclocephline scarabs and their host plants are documented as highly specialized plant–pollinator associations, with various fine‐tuned adaptations. We studied the association between Philodendron adamantinum, a species endemic to the Espinhaço Range in Minas Gerais, South‐East Brazil, and its exclusive pollinators. We focused on the pollination mechanism and reproductive success of P. adamantinum, analysed its floral scent composition, and performed field bioassays to verify the scent‐mediated attraction of pollinators. The reproductive success of P. adamantinum depends on the presence of Erioscelis emarginata (Scarabaeidae, Cyclocephalini), its sole pollinator. At dusk, the inflorescences heat up to 18 °C above the surrounding ambient air temperature and give off a strong sweet odour, from which 32 volatile compounds were isolated. Dihydro‐β‐ionone, the major constituent in the floral scent bouquet, lures individuals of E. emarginata when applied to scented artificial decoys, either alone or blended with methyl jasmonate. We attribute the low fruit set of P. adamantinum at our study sites to pollinator limitation of small and isolated populations and geitonogamic pollen flow of vegetatively generated clonal plant groups. The interaction between P. adamantinum and E. emarginata shows common traits typical of the known plant–pollinator associations involving cyclocephaline scarabs: the asymmetrical dependence of plants on their pollinators, and the scent‐mediated interaction between flowers and beetles. In addition to updating the current catalogue of active compounds of cantharophilous pollination systems, further experimental studies should elucidate the role of the specific chemical compounds that attract pollinators along different time and biogeographic scales. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 679–691.     

Geographical variation in floral traits of the tree tobacco in relation to its hummingbird pollinator fauna

Nicotiana glauca , a hummingbird pollinated plant, exhibits geographical variation in several floral traits. We examined whether geographical differentiation occurred for different flower characters and if this differentiation could be explained, at least in part, by the existence or abundance of different hummingbird species in the respective pollinator assemblages. The comparison between five populations showed significant variation in six floral traits and two female fitness measures. The traits that better discriminated between populations were corolla length and corolla width. There were metric correlations between corolla length and style length in all populations studied and, in four of the five populations, both corolla length and width were also correlated. Among plants in each population, seed weight was correlated positively and significantly with style exertion, suggesting that fruit quality is dependent on the degree of cross pollination. Assemblages of hummingbirds differed between populations in species composition, visitation frequencies, and bill length. Linear regression involving bill length of the more frequent hummingbird pollinators and corolla length yielded positive and significant relationships. Thus, there appears to be an adjustment between pollinators and flowers traits that have high incidence in the among population variation.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 657–667.     

Pollination biology of the deceptive orchid Changnienia amoena

The pollination biology of Changnienia amoena , an endangered terrestrial orchid, was investigated at two sites in the Shennongjia Mountains, Hubei, central China. The results show that the orchid is exclusively pollinated by bumblebees. In Longmenhe, Bombus ( Diversobombus ) trifasciatus is the primary effective pollinator, whereas B.  ( Tricornibombus ) imitator is the only pollinator in Guanmenshan. These two bumblebees can be treated as a functional group because they carry pollinaria on the same position on their bodies and have similar pollinating behaviours. The morphological traits of the flower adapt precisely to the pollinators. Visitation by bumblebees is mainly in the first half of the flowering period of C. amoena . Pollinarium removal and pollinia deposition take place when bumblebees withdraw from the flower. Crossing experiments show that C. amoena is a self-compatible and outcrossing species. Fruit set in this species is low and may result from limited pollinators because 87.5% of individuals set fruits under hand-pollination, but only 6–12% of individuals set fruits under natural conditions. These results imply that it is important to conserve the pollinator community together with the plants when conservation management for this endangered species is undertaken. Artificial pollination would also be a useful measure to facilitate restoration of the small populations.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 165–175.     

Diversity, flower visitation frequency and generalism of pollinators in temperate rain forests of Chiloé Island, Chile

Species richness and taxonomic composition of pollinator assemblages are documented for 26 plant species from temperate rain forests of northern Chiloé Island, southern Chile (42°30'S). We investigated the patterns of generalism and specialization among plants and animal pollinators by comparing the flower visit frequency by different pollen vectors during the spring and summer months of three consecutive years (2000–2002). Species studied exhibited a range of floral morphologies (radial vs. zygomorphic, open vs. tubular) and rewards (nectar and/or pollen). Overall, we recorded 172 pollinator species, with an average of 6.6 species of pollen vectors/plant species. Pollinators visited an average of 15.2 plant species/pollen vector. Pollinator assemblages were dominated by Coleoptera (75 species), Diptera (56 species) and Hymenoptera (30 species), but passerine birds and hummingbirds were also important. The most specialized plants were vines, including the bee-pollinated genus Luzuriaga (Philesiaceae) and two endemic species of hummingbird-pollinated Gesneriaceae. Hymenoptera contributed 41.2% of all visits, with the bumblebee Bombus dalhbomii accounting for 22.5% of these. Plants with unspecialized flower morphology supported a higher species richness of pollinators, but visiting rates did not differ from specialized flowers.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 147 , 399–416.     

Many to flower, few to fruit: the reproductive biology of Hamamelis virginiana (Hamamelidaceae)

Hamamelis virginiana flowers from late September to late November. In 1977, we began studying the reproductive biology of this eastern North American arborescent shrub by examining floral phenology and rewards, pollen-ovule ratios, breeding system, pollination, pollinator and resource limitation, and seed dispersal. The homogamous, self-incompatible flowers emit a faint odor, bear nectar with sucrose ratios typical of bee- and fly-pollinated flowers, and produce abundant sticky pollen. Flowers were visited infrequently by insects representing six orders. Flies were the most common floral visitors, specifically members of the genus Bradysia, but small bees also carried high percentages of Hamamelis pollen. Despite high pollen/ovule ratios (11?445 grains/ovule), bees and flies are likely pollinators, as experiments indicate wind pollination is less likely. Pollen quantity and resource availability did not appear to limit reproductive output, but pollen quality did. Tests of >40?000 flowers showed natural fruit set to be <1%. The flowering time, breeding system, and clumped distribution of plants, likely due in part to limited seed dispersal, combine to yield this remarkably low fruit set. Because all other species of Hamamelis flower from late winter to early summer, it may be that H. virginiana evolved a fall flowering phenology to avoid competition for pollinators with the closely related H. vernalis.     

Pollination and reproduction of Psychotria homalosperma,an endangered distylous tree endemic to the oceanic Bonin (Ogasawara) Islands,Japan

Distyly is usually rare or not observed in species thriving on oceanic islands. The rarity of this breeding system is probably because of the difficulty of colonization for distylous plants and the paucity of pollinators on oceanic islands. However, the endemic and endangered tree Psychotria homalosperma has maintained its distylous nature in the oceanic Bonin Islands, Japan. To understand how the distylous breeding system of P. homalosperma has been maintained on these islands and to characterize the reproduction systems, we studied the pollination and reproductive biology of this species. Specifically, we observed current flower visitors and estimated their effects on plant reproduction. We also examined the floral traits and floral volatiles of P. homalosperma to infer its original pollinators, because plant–pollinator relationships in the Bonin Islands have recently been disrupted by anthropological activities. Finally, we examined the fruit set and pollen tube growth in the stigmas under hand and open pollination. Although original pollinators were presumed to be moths with long proboscises, the introduced honeybee, Apis mellifera, was the most common flower visitor. The honeybee carried pollen grains only unidirectionally, from the short‐ to long‐styled morphs, because it could not reach the hidden stigmas of the short‐styled flowers, and long‐styled flowers set fruits 1.7–38 times more than short‐styled ones. This case study indicates that the instability of pollinator fauna can cause distylous species to be rare on oceanic islands.     

Reproductive biology of Boswellia serrata, the source of salai guggul, an important gum-resin

Detailed studies were carried out on the phenology, floral biology, pollination ecology and breeding system of Boswellia serrata Roxb. (Burseraceae) the source of 'salai guggul'. The trees remain leafless during the entire period of flowering and fruiting. The inflorescence is a terminal raceme and produces up to 90 bisexual, actinomorphic flowers. On average a flower produces 10 044 ± 1259 starch-filled pollen grains. About 85% of the fresh pollen grains are viable; the pollen to ovule ratio is 3348 : 1. The stigma is of the wet papillate type. The style is hollow with three flattened stylar canals filled with a secretion product. The stylar canals are bordered by a layer of glandular canal cells. The inner tangential wall of the canal cells shows cellulose thickenings. The ovary is trilocular and bears three ovules, one in each locule. Flowers offer nectar and pollen as rewards to floral visitors. The giant Asian honey bee ( Apis dorsata ) and A. cerana var. indica (Indian honey bee) are the effective pollinators. The species is self-incompatible and the selfed pollen tubes are inhibited soon after their entry into the stigma. Self-pollen tubes develop a characteristic 'isthmus' as a result of enlargement of the tube soon after emergence through the narrow germ pore. Cross-pollinated flowers allowed normal pollen germination and pollen tube growth, and resulted in fruit- and seed-set. Under open pollination fruit-set was only about 10%. Although manual cross-pollinations increased fruit set, it was only up to about 20%. Low fruit set appears to be the result of inadequate cross-pollination and other constraints, presumably limitation of available nutrients.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 147 , 73–82.     

Reflexed flowers in Aeschynomene amorphoides (Fabaceae: Faboideae): a mechanism promoting pollination specialization?

This study aims to understand the role of floral traits in determining the reproductive biology of the leguminous shrub Aeschynomene amorphoides, endemic to western Mexico, which has unusually orientated flowers. We investigated the floral biology, pollination and breeding system based on a combination of morphological studies and field experiments, using controlled pollinations in a natural environment. The architecture and reflexed position of A. amorphoides flowers facilitate precise placement of pollen on the body of the pollinator, but this has a cost to A. amorphoides in terms of available flower resources. These costs to reproduction success are set against the attraction of a specialized pollinator, Tetraloniella jaliscoensis, which is capable of manipulating this unique pollination system in papilionoid (or flag) flowers. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 657–666.     

A ballistic pollen dispersal system influences pollination success and fruit‐set pattern in pollinator‐excluded environments for the endangered species Synaphea stenoloba (Proteaceae)

The critically endangered Synaphea stenoloba (Proteaceae) has numerous scentless flowers clustered in dense inflorescences and deploys a ballistic pollen ejection mechanism to release pollen. We examined the hypothesis that active pollen ejection and flowering patterns within an inflorescence influence the reproductive success (i.e. fruit formation) of individual flowers within or among inflorescences of S. stenoloba in a pollinator‐excluded environment. Our results showed that: (1) no pollen grains were observed deposited on the stigma of their own flower after the pollen ejection system was manually activated, indicating self‐pollination within an individual flower is improbable in S. stenoloba; (2) fruit set in the indoor open pollination treatment and the inflorescence‐closed pollination treatment indicated that S. stenoloba is self‐compatible and pollen ejection can potentially result in inter‐floral pollination success; (3) fruit set in the inflorescence‐closed pollination treatment was significantly lower than that of indoor open pollination, indicating within‐ and between‐flower pollination events in an inflorescence are most likely limited, with pollination between inflorescences providing the highest reproductive opportunity; and (4) analysis of the spatial distribution of cumulative fruit set on inflorescences showed that pollen could reach any flower within an inflorescence and there was no functional limitation on seed set among flowers located at various positions within the inflorescence. These data suggest that the pollen ejection mechanism in S. stenoloba can enhance inter‐plant pollination in pollinator‐excluded environments and may suggest adaptation to pollinator scarcity attributable to habitat disturbance or competition for pollinators in a diverse flora. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 170 , 59–68.     

Relationships between floral characters, pollination mechanisms, life forms, and habitats in Araceae

The floral traits of the inflorescences of angiosperms have coevolved to ensure and maximize pollination success. Other factors believed to influence floral architecture are external (for example, ecological) to the inflorescence. In order to understand the relationships between such factors and floral characters, 12 floral traits were measured in 54 species of Araceae. An analysis was performed to determine how these traits are linked to the following: (1) self-pollination capacity; (2) life form (evergreen versus seasonally dormant); (3) climatic conditions; and (4) type of pollinator (i.e. flies, bees, or beetles). A significant difference was found between the pollen to ovule ratio of the species able to self-pollinate and those unable to self-pollinate. Evergreen and tropical aroids produced a larger number of gametes than did seasonally dormant and temperate taxa. Finally, several floral traits, such as pollen volume and number, number of female flowers, and flower sexual type (unisexual or bisexual), showed clear differences between the three pollinator types. Variations in floral traits between the different life forms and climatic conditions are discussed with respect to pollination efficiency and properties of the growing season. The pollen to ovule ratio cannot be considered as an accurate indicator of breeding systems in aroids because of the particular pollination ecology of the family.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 29–42.