Pollination biology of a night‐flowering Galápagos endemic,Ipomoea habeliana (Convolvulaceae)

Ipomoea habeliana is an endemic, night‐flowering member of the Galápagos flora. Pollination experiments, flower‐visitor observations, nectar sampling, pollen transfer, and pollen to ovule ratio and pollen size studies were included in this project. The large, white flowers of this species set fruit via open pollination (55%), autonomous autogamy (51%), facilitated autogamy (91%), cross‐pollination (80%), diurnal open pollination (60%) and nocturnal open pollination (60%). Fruit set is pollen‐limited. Ants, beetles, crickets and hawk moths regularly visit the flowers. Ants are the most frequent visitors, but hawk moths are the only effective pollinators. Nectar is available throughout the night, but is most abundant early in the evening when hawk moth visits are most frequent. Experiments with fluorescent dust demonstrate intra‐ and inter‐plant pollen movement by hawk moths. Although this species is adapted for hawk moth pollination, it readily sets fruit via autonomous autogamy when no visits are made. Thus, it is concluded that it is facultatively xenogamous. Additional support for this conclusion is provided by the pollen to ovule ratio of 1407 and by the fact that the plants grow in a region that has few or no faithful pollinators. Conservation efforts for I. habeliana should include hand pollinations, which could significantly increase seed set. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 11–20.     

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.     

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.     

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.     

Floral biology and pollination mechanisms of four Mexico-endemic Fuchsia species with contrasting reproductive systems

Aims The evolution of the outstanding variation of reproductive systems in angiosperms has been considered an important driver of lineage diversification. Closely related hermaphroditic and dioecious species with biotic pollination provide the opportunity to study and compare traits related to pollinator attraction and their consequences on reproductive components. A higher predictability of pollination syndromes is expected in dioecious species, which are dependent on pollinators, than in self-compatible hermaphroditic taxa. Dioecious species may suffer pollen limitation depending on the quality of floral rewards and the kind and abundance of pollinators, whereas no pollen limitation is expected in hermaphroditic species with autonomous self-pollination. Additionally, in the absence of pollen limitation, more or better seeds are expected in dioecious species, according to the sexual specialization hypothesis.Methods In natural populations of the hermaphroditic Fuchsia fulgens and Fuchsia arborescens and dioecious Fuchsia parviflora and Fuchsia obconica, all endemic to Mexico, we first described flower phenology, flower production and longevity and nectar volume and concentration. Then, we evaluated the correspondence between floral visitors and pollination syndromes. In hermaphrodite plants, we determined the level of herkogamy and the potential for autonomous self-pollination. Finally, we evaluated the effect of pollen limitation on fruit set and seed number and assessed seed germination for all species.Important findings In contrast to our prediction, dioecious species did not show a higher correspondence between pollination syndromes and floral visitors than did hermaphrodites; however, male flowers exhibited a higher correspondence than female flowers. No pollen limitation was detected in dioecious species, for which visitation rate did not differ between male and female flowers. The hermaphroditic F. fulgens showed pollen limitation for seed number, despite the presence of autonomous selfing. Fruit set from autonomous pollination was higher in F. arborescens, which showed a lower level of herkogamy compared with F. fulgens. Finally, dioecious species produced fewer but heavier seeds compared with hermaphrodite species. Although Fuchsia is classified as an outcrossing genus, both hermaphroditic species showed autonomous self-pollination. The heavier but lower number of seeds per fruit in dioecious species may be related to the more efficient resource allocation expected from sexual specialization. This could play an important role in the evolution of dioecy; however, a comparative phylogenetic approach is required to confirm this hypothesis.     

Resource limitation and pollen source (self and outcross) affecting seed production in two louseworts, Pedicularis siphonantha and P. longiflora (Orobanchaceae)

Two animal-pollinated hermaphrodite plants, Pedicularis siphonantha and P. longiflora , have been used to investigate factors limiting seed production in natural populations. To evaluate the potential seed abortion due to resources limitation, seed development has been observed and seed count conducted twice. Seed production per capsule has been compared when flowers have been removed and in a control group. Open pollination has been investigated and pollen supplementation undertaken to estimate the possibility of pollen limitation. Results show that seed abortion is frequent. Stigmatic pollen load is significantly higher than ovule number per ovary under open pollination for both species. Additional self and outcross pollen did not affect seed production. Flower removal significantly increases seed production per capsule, which indicates that seed production of the studied species is limited by available resources. To detect differences in seed production between flowers pollinated by self and outcross pollen, hand pollination of bagged flowers has also been conducted in natural populations of the two Pedicularis species. Compared with open pollination, hand-pollinating self-pollen decreases, while outcross pollen increases seed production per capsule. Such results suggest that inbreeding depression in the two self-compatible species may also result in partial seed abortion under open pollination if mixed pollen is deposited on the stigma. Our results also suggest that pollen interference plays an important role in low female fertility in the two Pedicularis species.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 147 , 83–89.     

海南三七（姜科）的食源性欺骗传粉

有花植物为繁殖成功,进化出各种各样的花部特征来吸引传粉者,如为传粉者提供花蜜、花粉、栖息地等,然而在33科146属的被子植物中也存在着不提供任何报酬而欺骗昆虫为其传粉的现象。这种欺骗性传粉模式主要出现在高度进化的具有多样化传粉模式的兰科植物中。报道了在姜科植物中首次发现的食源性欺骗传粉模式。对姜科山柰属海南三七进行连续2年的传粉生物学观察和研究发现,海南三七的花在早上5:30～6:00之间开放,下午17:00～18:00左右闭合萎蔫,持续大约11～12h。开花过程中花粉活性与柱头可受性均保持较高水平(>90%)。花粉/胚珠比率(P/O)为82.20±47.89(n=20)。木蜂是其主要的访花和传粉昆虫,访花目的是吸取花蜜。海南三七虽有细长线形的蜜腺,但并不分泌花蜜作为传粉昆虫访花的报酬,采用食源性欺骗的方式欺骗木蜂为其传粉。繁育系统的研究表明广西弄化的海南三七居群主要是通过根茎进行无性繁殖。     

草豆蔻传粉生物学的研究

比较研究了花柱卷曲性植物草豆蔻 Alpinia hainanensis两种表型(上举型和下垂型)的传粉生物学特性。结果表明:草豆蔻的花柱卷曲运动节律与其他已报道的山姜属Alpinia植物基本一致,而下垂型花的花柱卷曲运动明显滞后于上举型花约2 h。草豆蔻的花柱卷曲运动中存在一些不同步的现象,甚至在同一花序上的两朵花的花柱运动节律亦会表现出不一致的现象,但上举型花的花药开裂时间却严格同步,都发生在同类型个体的柱头全部位于花药上方之后进行。草豆蔻上举型花的花蜜分泌量、单花花粉量、花粉/胚珠比率(P/O)均明显比下垂型花多,而两种表型的胚珠数、花蜜糖含量、氨基酸含量无显著差异。在草豆蔻的单花期内不同时间段进行人工授粉,上举型花在其柱头位于花药下方时进行人工授粉,其结实率明显比柱头位于花药上方时人工授粉的处理高,下垂型花则没有显著差异。在自然居群中,草豆蔻的主要传粉者是无垫蜂Ameglla sp.和两种木蜂Xylocopa sp.,但存在传粉者不足而影响结实率的现象。完全套袋、去雄和去雌(去柱头)处理的均不结实,表明草豆蔻中不存在无融合生殖、主动自花授粉和滞后自交的生殖保障现象。而人工自交和异交均具有较高的结实率,表明草豆蔻为自交亲和植物。草豆蔻的繁育系统是具花柱卷曲性运动的异花授粉的交配系统。     

Pollination by fungus gnats in four species of the genus Mitella (Saxifragaceae)

The first example of pollination by fungus gnats in the eudicots is reported. The genus Mitella (Saxifragales) is characteristically produces minute, inconspicuous, mostly dull-coloured flowers with linear, sometimes pinnately branched, petals. To understand the function of these characteristic flowers, we studied the pollination biology of four Mitella species with different floral traits and different sexual expression: dioecious M. acerina , gynodioecious M. furusei var. subramosa , and hermaphroditic M. stylosa var. makinoi and M. integripetala. Flower-bagging experiments showed that wind pollination did not occur in the dioecious and gynodioecious species. Two years of observations of flower visitors at six study sites in Japan revealed that the principal pollinators of all four Mitella were specific species of fungus gnats (Mycetophilidae), which landed on the flowers with their long spiny legs settling on the petals. Characteristically, numerous pollen grains were attached to the fungus gnats in specific locations on the body. Although, on average, 1.3–2.6 fungus gnats visited each inflorescence per day, the fruit set of both bisexual and female flowers exceeded 63%. These results suggest that fungus gnats are highly efficient pollinators of Mitella spp., and that Mitella flowers are morphologically adapted to pollination by fungus gnats.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 144 , 449–460.     

Pollen fates and the limits on male reproductive success in an orchid population

Male reproductive success in higher plants depends largely on the fates of pollen, but current methodologies have given only partial insights into this important aspect of plant mating. We present a detailed analysis of the proportions and absolute amounts of stained pollen involved in six key fates for the hawkmoth-pollinated African orchid Disa cooperi . Despite being packaged into pollinaria, high proportions (> 0.95) of the pollen removed from anthers were lost during transport by hawkmoths in both years. The proportion of pollen lost correlated positively with the number of pollinaria removed from a plant, so that pollen export did not vary with pollen removal. Most pollen was dispersed to neighbouring plants, with rare long-distance dispersal up to 65 m. Of the pollen that reached stigmas during both years, roughly equal amounts were involved in facilitated self-pollination vs. cross-pollination, but the relative proportions of these fates differed between years. Contrary to expectation, we found that self-pollination between flowers did not increase with the number of open flowers, even though moths probed significantly more flowers on larger plants. However, during both years the fraction of removed pollen exported to other plants declined significantly with increasing self-pollination on the source plant, indicating that once self-pollination occurred it reduced (discounted) subsequent pollen export opportunities. The packaging of pollen into pollinaria in orchids appears to increase overall transfer efficiency by at least an order of magnitude relative to plants with granular pollen. Nevertheless, considerable uncertainties remain in the male reproductive success of individual orchids. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 86 , 175–190.     

Flowering in a bamboo, Melocanna baccifera (Bambusoideae: Poaceae)

Melocanna baccifera (Roxburgh) Kurtz ex Skeels, a species of bamboo introduced to Sri Lanka from India, flowered and set fruit during 2001–2002. Culms that flowered and set fruit died. The incidence of flowering is significant in that flowering took place close to the predicted mast flowering in 2007. At the onset of flowering, inflorescences were predominantly staminate. But later in 2002, bisexual and pistilate flowers also developed leading to fruiting. Both protandry and protogyny were observed in the bisexual florets. Floral characters indicated that the species was mainly out-crossing. Although anther dehiscence released pollen and stigmas were exerted, pollination of stigmas was inefficient. The few stigmas that were naturally pollinated showed limited pollen tube growth. However, fruit set took place. Fruits were very rarely seen to germinate naturally. Many fruits were devoid of an embryo, indicating that parthenocarpy and/or apomixis may have taken place. Excised embryos germinated in vitro .  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 143 , 287–291.     

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.     

Specialized use of pollen vectors by Caesalpinia gilliesii, a legume species with brush-type flowers

The pollination of Caesalpinia gilliesii (Fabaceae) , a legume species with long, brush-type flowers, was studied in wild populations in Argentina. A total of 341 hawkmoths (Sphingidae), belonging to 10 species, with tongues ranging from 1.5 to 13.5 cm in length, were captured by means of light traps. Hawkmoths could be classified in four significantly different tongue-length classes or guilds: short (15.35 ± 1.11 mm), medium (30.23 ± 2.24 mm), long (55.85 ± 4.98 mm) and very long (95.61 ± 13.63 mm). A total of 133 of the hawkmoths, belonging to seven species, carried pollen of Cae. gilliesii , mainly on their venter. Successful contact with anthers while drinking nectar depended upon hawkmoth tongue length. The relative frequency of pollen-carriage and the mean tongue length of each species were positively and significantly correlated. Considering a null hypothesis of nonspecialization, in which hawkmoths carrying pollen are distributed at random among individuals of the four guilds, long-tongued hawkmoths carried Cae. gilliesii pollen more frequently than would be expected by chance. In contrast, short- and medium-tongued guilds carried pollen less frequently than is predicted by random expectation. Individuals with short tongues accessed nectar from below without touching the anthers, whereas very long-tongued hawkmoths, with tongues longer than the length range of the flower reproductive organs, can probably reach nectar without touching the fertile organs. Results show that a pterotribic pattern of pollen deposition on the body of long-tongued hawkmoths is operating in this species. This suggests that brush-type blossoms are not necessarily unspecialized, despite popular belief.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 579–592.     

Visual signalling of nectar‐offering flowers and specific morphological traits favour robust bee pollinators in the mass‐flowering tree Handroanthus impetiginosus (Bignoniaceae)

Mass flowering is a widespread blooming strategy among Neotropical trees that has been frequently suggested to increase geitonogamous pollination. We investigated the pollination ecology of the mass‐flowering tree Handroanthus impetiginosus, addressing its breeding system, the role in pollination of different visitors, the impact of nectar robbers on fruit set and the function of colour changes in nectar guides. This xenogamous species is mainly pollinated by Centris and Euglossa bees (Apidae) seeking nectar, which are known to fly long distances. The flowers favour these bees by having: (1) a closed entrance in newly opened flowers which provides access only to strong bees capable of deforming the flower tube; and (2) a nectar chamber that is accessible only to long‐tongued bees. Only first‐day flowers with yellow nectar guides produce nectar. Pollinators prefer these flowers over second‐ and third‐day flowers with orange and red nectar guides, respectively. Nectar robbers damage two‐thirds of the flowers and this robbing activity decreases fruit set by half. We attribute the low fruit set of H. impetiginosus to the intense nectar robbing and hypothesize that visual signalling of nectar presence in newly opened (receptive) flowers reduces geitonogamy by minimizing bee visits to unrewarding (non‐receptive) flowers. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 176 , 396–407.     

Pollination of the heterostylous Galápagos native, <Emphasis Type="Italic">Cordia lutea</Emphasis> (Boraginaceae)

The hypothesis of this study was that in the Galápagos Islands, fruit and seed set via nocturnal pollination would exceed that of diurnal pollination due to greater insect activity at night typical of hot, arid regions. Cordia lutea, a heterostylous member of the Galápagos flora, was submitted to pollination experiments, visitor observations, nectar sampling, pollen transfer studies, pollen-ovule ratio studies, and pollen measurements. Flowers set fruit and seed via open pollination, autonomous autogamy, facilitated autogamy, facilitated cross-pollination, diurnal pollination, and nocturnal pollination. There was a significant difference in fruit set between flowers experiencing legitimate cross-pollinations (pin × thrum) and those experiencing all other pollination treatments except facilitated autogamy. There was no significant difference in seed set among any of the treatments, but there was a trend toward greater seed set for flowers experiencing open-pollination, legitimate cross-pollination, and nocturnal pollination. There was no significant difference in fruit set or seed set between flowers experiencing diurnal pollination and nocturnal pollination, although there was a trend toward greater seed set resulting from nocturnal pollination. Carpenter bees were the most effective diurnal pollinators, whereas moths were the most effective nocturnal pollinators. Of the two, moths are more efficient at transporting pollen from plant to plant. Results indicate that an overall low productivity of this species is due to pollen limitation exacerbated by nectar robbing. Cordia lutea exhibits a mixed mating system, producing a relatively low level of fruits through a combination of self- and cross-pollination, facilitated by the relatively few insects that are available.     

Nocturnal and diurnal pollination of Clerodendrum molle (Verbenaceae) in the Gal��pagos Islands

The primary hypothesis of this study was that in the Galápagos Islands, fruit and seed set via nocturnal pollination would exceed that of diurnal pollination because of the greater insect activity at night typical of hot, arid regions. Clerodendrum molle, a widespread member of the Galápagos flora was submitted to pollination experiments, visitor observations, nectar sampling, pollen transfer studies, pollen?Covule ratio studies, and pollen measurements. Flowers set fruit and seed via open pollination, autonomous autogamy, facilitated autogamy, facilitated cross-pollination, diurnal pollination, and nocturnal pollination. Results indicate no significant difference in fruit set. Cross-pollinated flowers showed a significant increase in seed set over all treatments except facilitated autogamy. Nocturnal and diurnal fruit and seed set did not differ significantly. Nocturnal visitors included ants, spiders, hawk moths, and roaches whereas diurnal visitors included carpenter bees and ants. Galápagos members of C. molle exhibit incomplete protandry and set fruit via autonomous autogamy as a result of natural selection in an environment with few faithful pollinators. Overall low fruit and seed set are likely because of a combination of pollen and resource limitation, the latter exacerbated by nectar robbing. Studies of island angiosperms are crucial for complete understanding of the population dynamics of indigenous plants, which can assist conservation officials in protecting these species.     

The pollination biology of Sauroglossum elatum Lindl. (Orchidaceae: Spiranthinae): moth-pollination and protandry in neotropical Spiranthinae

The pollination biology of Sauroglossum elatum Lindl (Orchidaceae: Spiranthinae) was studied in the State of São Paulo, south-eastern Brazil. This orchid is protandrous and almost fully self-compatible, but pollinator-dependent. Thus, pollinators are required for the plants to set fruits and seeds. The flowers are pollinated by moths of the family Noctuidae. Pollinia are dislodged when the moths probe flowers in the male phase. At this stage the stigmatic surface is inaccessible, so that the flowers can act only as pollen-donors. Flowers in the female phase present their stigmatic surfaces well exposed and dry viscidia; at this stage the flowers act as pollen receivers. Pollinarium-bearing moths, when visiting a flower in the female phase, will brush the pollinarium against the stigmatic surface, thus effecting the pollination. Moth-pollination is reported here for the first time for the orchid subtribe Spiranthinae. Protandry also occurs in a few additional Brazilian Spiranthinae. Based on the evidence presented in this work, protandry in Spiranthinae is not necessarily linked to bumblebee pollination, as currently accepted. It is suggested that the occurrence of protandry in Spiranthinae and in the closely related subtribes Prescottinae and Goodyerinae may also be a feature encompassing ecological and phylogenetic implications. Anecdotal ex-situ observations are briefly discussed. Cultivated specimens were actively visited by Tetragonisca angustula (Meliponini) bees. which broke the pollinaria, collected the pollen and eventually performed pollination by leaving small fragments of the pollinia on the stigmatic surface. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 138 , 9–16.     

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.     

The effectiveness of some mechanisms of reproductive isolation in Arum maculatum and A. italicum (Araceae)

Mechanisms of reproductive isolation were studied in two species of Arum , A. italicum and A. maculatum , growing in England and the south of France. The study focused on three potential mechanisms for reproductive isolation: the effectiveness of dichogamy as a barrier to autogamy; the ability of self and outcrossed pollen to germinate on stigmas at different stages of anthesis and to effect pollination; and postzygotic barriers to selfing. Dichogamy was found to provide a very effective barrier to within-inflorescence selfing in these species, as no seeds were produced by spontaneous self-pollination (i.e. autogamy) in any population of either species. However, the study found that geitonogamy (cross-pollination between inflorescences of a same individual or clone) was possible, as genotypes frequently produced several inflorescences and stigmas were found to be receptive to pollen from before anthesis until their contraction at the end of the female phase of flowering. Hand pollination with self pollen from clone inflorescences produced as numerous and heavy seeds as outcross pollination. In addition, the germination and growth of geitonogamously produced seed was similar to that of outcrossed seed, suggesting that this potential postzygotic barrier is absent or weak. These findings suggest that geitonogamous seed production may be unrestricted by significant pre- or postzygotic barriers. The possible advantages of geitonogamy in Arum are discussed.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 323–328.     

Effects of pollen shortage and self-pollination on seed production of an endangered tree, Magnolia stellata

BACKGROUND AND AIMS: Pollen limitation is a significant determinant of seed production, and can result from both insufficient pollen quantity (pollen shortage) and quality (mainly relating to self-pollination). For animal-pollinated tree species with large floral displays, pollen limitation may be determined by a balance between increased pollen quantity due to increased attractiveness for pollinators, countered by increased self-pollination due to increased geitonogamy. The contributions of pollen shortage and self-pollination on seed production were quantitatively examined in the natural pollination of an insect-pollinated, dichogamous, endangered tree, Magnolia stellata, which has a large, showy floral display. METHODS: Manual self- and cross-pollinations were conducted to determine the effects of selfing on seed production. The outcrossing rate was measured using microsatellite analyses of open-pollinated seeds, and the embryo mortality rate caused by self-pollination was indirectly estimated. The frequency of ovule mortality due to pollen shortage was also inferred using the embryo mortality and ovule survival rates from natural pollination. KEY RESULTS: The average fruit set, seed set per fruit, and ovule survival rate per tree from hand cross-pollination were 1.37, 3.15, and 3.34 times higher than those from hand self-pollination, respectively, indicating that self-pollination causes inbreeding depression for fruit and seed set. The multilocus-outcrossing rate (t(m)) was intermediate, 0.632, and the primary selfing rate was 0.657. This indicates that frequent geitonogamous selfing occurs. The ovule mortality rate due to pollen shortage and the embryo mortality rate due to self-pollination were estimated to be 80.8 % and 45.9 %, respectively. CONCLUSIONS: It is concluded that seed production of M. stellata is strongly limited by both pollen shortage and self-pollination. Inefficient beetle-pollination and the automimicry system via asynchronous flowering might be responsible for the high level of pollen shortage and frequent geitonogamy. This is despite a large, showy floral display and the dichogamous system of the species.