Flowering phenology and reproductive biology of Drosera anglica (Droseraceae)

Prompted by the sparse knowledge of the reproductive biology of carnivorous plants, compared with studies of their trapping habits, we investigated the flowering phenology and pollination biology of Drosera anglica Huds. in two fens in mid-western Canada. Seed set and germination were used to compare the effectiveness of a series of pollination treatments, including single insect visits to virgin flowers. Flowers opened during mid-morning but closed by early afternoon, and exhibited pseudo-cleistogamic behaviour in cool, overcast weather. D. anglica was found to be self-compatible, and able to self-pollinate and self-fertilize. Geitonogamy was an uncommon mode of self-reproduction because plants typically possessed a lone inflorescence upon which a single, short-lived flower opened, a few days before the next bud reached anthesis. Insect visits to the fragrance-lacking, nectarless flowers, chiefly by flies (Diptera: Syrphidae), were infrequent (one visit per 1 h 40 min of observation), and the low frequency of seed set and low numbers of seeds per fruit in pollination treatments involving insects, suggest the species does not rely on insects to effect pollination. Self-pollination, with or without the aid of a vector (insects, wind) was as effective as natural pollination; ultimately, autogamy is chiefly responsible for natural seed set. Thus, the species exhibits characteristics of facultative autogamy.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 147 , 417–426.     

Reproductive biology of Arum italicum (Araceae) in the south of France

The reproductive success of Arum italicum in south-western France showed a positive relationship with plant vigour at both the plant (number of inflorescences) and inflorescence (number of seeds) levels. However, the infructescence and berry numbers were not related to the number of inflorescences, and two-fold more seeds were produced by individuals flowering several times than by those flowering just once. Moreover, the reproductive success of this species appeared to be limited by the high abortion rate (50%), strong predation pressure on the inflorescences (34%), and low seed set rate of nonpredated inflorescences (36%), suggesting pollination limitation. Nevertheless, a positive relationship was found between the mean number of Psychoda trapped per inflorescence and the number of maturing infructescences, particularly for the most abundant species, Psychoda crassipenis . Therefore, pollinator availability appeared to be an important limiting factor for fructification in the studied population, by contrast with other studies in which the fruit set appeared to be related more strongly to the density of inflorescences. Such different results may have been caused by the relatively low abundance of Psychoda in the present study.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 43–49.     

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.     

Pollination of Kadsura longipedunculata (Schisandraceae), a monoecious basal angiosperm, by female, pollen-eating Megommata sp. (Cecidomyiidae: Diptera) in China

The plants of Kadsura longipedunculata (Schisandraceae) are monoecious and possess either red or yellow male flowers (the androecium), with yellow tepals, and yellow female flowers. All flower types simultaneously produce heat and floral odours (dominated by methyl butyrate) throughout a 4–5-h nocturnal period. The flowers are pollinated only by female, pollen-eating Megommata sp. (Cecidomyiidae). Pollen is the only reward, and female flowers use the same attractants as male flowers but offer no food (pollination by deceit). Open pollinated flowers in nature varied in fruit set from 8 to 92%. Megommata (subfamily Cecidomyiinae, supertribe Cecidomyiidi), consists of six described species, which feed on Coccoidea (scale insects) and are distributed worldwide.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 523–536.     

Comparative biology of pollination systems in the African-Malagasy genus Brownleea (Brownleeinae: Orchidaceae)

The role of pollinators in the evolution of the African-Malagasy orchid genus Brownleea (Brownleeinae) was investigated. Taxa show specialization for pollination by bees ( B. parviflora , B. recurvata ), short-proboscid flies ( B. galpinii ), and long-proboscid flies ( B. macroceras , B. coerulea ). All species in the genus produce nectar, but some ( B. coerulea , B. galpinii ) appear to mimic flowers of abundant sympatric species as an additional strategy to attract pollinators. Species investigated in terms of their breeding systems ( B. coerulea , B. parviflora , B. macroceras , B. galpinii ) are reliant on pollinator visits for seed production. Self-pollination results in strong inbreeding depression during embryo formation. A phylogeny of the genus, constructed using data from the ITS1-5.8S-ITS2 region and morphology, indicates that fly pollination is likely to be basal in the genus, and that there has been a single shift to bee pollination.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 65–78.     

Pollination of the understorey palm Calyptrogyne ghiesbreghtiana by hovering and perching bats

Inflorescences of the Central American understorey palm Calyptrogyne ghiesbreghtiana offer bats fruit-like flower tissue as reward for visitation. Bats visited the inflorescences in two different modes: frugivores (Phyllostomidae: Stenodermatinae, Carolliinae) foraged on the inflorescence while perched, whereas bats that were primarily nectarivores (Phyllostomidae: Glossophaginae) also consumed flower tissue, but did so while hovering. Fruit set was significantly lower in inflorescences that had received only hovering visits, indicating that perching behaviour offers better possibilities for pollen transfer. The pollination system of C. ghiesbreghtiana is probably adapted to perching frugivorous bats with nectar-specialist Glossophagines as non-optimal participants. Seen in an evolutionary perspective the C. ghiesbreghtiana– glossophagine bat interactions may demonstrate recruitment of new pollinators from non-destructive visitors.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 281–288.     

Experimental and phylogenetic evidence for floral mimicry in a guild of fly-pollinated plants

Mimicry, as an adaptive explanation for the resemblance between organisms, is not always readily distinguishable from, inter alia , coincidence, shared ancestry, or convergent evolution. We tested the hypothesis that two rare South African orchid taxa Brownleea galpinii ssp. major (nectar-producing) and Disa cephalotes ssp. cephalotes (non-rewarding) are mimics of the nectar-producing flowers of a relatively common species, Scabiosa columbaria (Dipsacaceae), with which they always occur sympatrically. Flowers of the orchids were apparently unscented and had similar dimensions and almost identical spectral reflectance to the flowers of Scabiosa . The orchids were pollinated exclusively by long-proboscid flies (Tabanidae and Nemestrinidae) that feed mainly on nectar in Scabiosa flowers. Choice experiments showed that these flies did not discriminate between the orchids and Scabiosa when alighting on their flat-topped inflorescences. However, flies were not attracted to related orchids dissimilar to Scabiosa , or to inflorescences of B. galpinii that had been artificially reconstructed in the shape of a spike, rather than a flat-topped capitulum. A phylogenetic analysis showed traits that give the orchids a resemblance to Scabiosa , such as a flat-topped inflorescence and cream floral colouration with dark spots and short spurs, to be mostly apomorphic features, and therefore likely to be relatively recent adaptations for mimicry. We caution that the term mimic should not be applied to species whose resemblance to another species is due entirely to plesiomorphic traits that, in all likelihood, evolved prior to the ecological association.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 289–304.     

Two new South American species of Struthanthus (Loranthaceae) posing a challenge to circumscription of neotropical genera

Two new, closely related species of Struthanthus (Loranthaceae) are described, S. meridionalis from southern Bolivia and S. prancei from northern Brazil, each showing significant deviations from the generic norm in their inflorescence morphology. In both cases, a very high proportion of inflorescences bear bracteolate and/or ebracteolate monads as lateral units rather than the triads which characterize the rest of the genus. The place of inflorescence morphology in the development of generic concepts in small-flowered neotropical Loranthaceae is briefly reviewed, leaving the two new species in Struthanthus for the time being.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 142 , 469–474.     

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.     

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.     

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.     

Any which way will do – the pollination biology of a northern Australian rainforest canopy tree (Syzygium sayeri; Myrtaceae)

The pollination biology of Syzygium sayeri was documented using the special capabilities of the Australian Canopy Crane. Syzygium sayeri is a xenogamous species with poor self-compatibility, moderate levels of natural out-crossing, and the producer of copious amounts nectar throughout the day and night. Of a diverse fauna associated with, and visiting the flowers of S. sayeri , larger vertebrates (blossom bats and honeyeaters) account for approximately half its natural pollination rate, while the balance of pollination is attributable to a host of invertebrate visitors (wasps, flies, thrips, butterflies). Day and night pollinators contributed approximately equally to the successful pollination of S. sayeri ; although the number of individuals visiting flowers was greater during the day, further experimentation might reveal night visitors to be more effective pollinators. The co-occurrence of vertebrates and invertebrates, as well as day and night visitors, suggests that S. sayeri has a generalist pollination system, whereby the absence of a discrete set of faunae could be compensated for by the presence of other pollinators. What is not clear is the contribution of different pollinators to the population success (i.e. gene flow) of this species. Further study is needed to determine the contribution of each pollinator group to the flow of genetic material in populations of S. sayeri . © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 149 , 69–84.     

The design of trapping devices in pollination traps of the genus Arum (Araceae) is related to insect type

Pollinators have long been known to select for floral traits, but the nature of this relationship has been little investigated in trap pollination systems. We investigated the trapping devices of 15 Arum spp. and compared them with the types of insects trapped. Most species shared a similar general design of trap chamber walls covered in downward‐pointing papillate cells, lacunose cells in the chamber wall and elongated sterile flowers partially blocking the exit of the trap. However, there was significant variation in all these morphological features between species. Furthermore, these differences related to the type of pollinator trapped. Most strikingly, species pollinated by midges had a slippery epidermal surface consisting of smaller papillae than in species pollinated by other insects. Midge‐pollinated species also had more elongated sterile flowers and tended to have a larger lacunose area. We conclude that pollination traps evolve in response to the type of insect trapped and that changes to the slippery surfaces of the chamber wall are an important and previously little recognized variable in the design of pollination traps. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 172 , 385–397.     

Morphological aspects and phylogenetic analyses of pollination systems in the Tylophora–Vincetoxicum complex (Apocynaceae-Asclepiadoideae) in Japan

Pollinators of two Cynanchum , five Tylophora , and 16 Vincetoxicum species were observed in 26 populations in Japan. The following pollination systems were observed in 18 species: moth pollination, generalized insect pollination, wasp pollination, dipteran pollination, both dipteran and moth pollination, and autogamy. Principal component analysis based on 13 floral characters indicated that the size of the pollinator tended to increase with sizes of all characters measured. Furthermore, species that have developed interstaminal parts of the corona and concealed stigmatic chambers tend to be pollinated by long-tongued insects. The phylogenetic distribution of pollinator types showed that species belonging to Clade I are pollinated exclusively by Diptera, whereas those of Clade II are pollinated by four insect orders. The most prominent pollinator transition in the Tylophora–Vincetoxicum complex is dipteran to moth pollination. The most common morphological change of the plants from dipteran pollination to moth pollination, or vice versa, is modification of the corolla. In the Tylophora–Vincetoxicum complex, pollination mode shifts are generally accompanied by modifications of the corona and the structure of gynostegium. One hypothesis for the rapid radiation observed in Clade II is that a widely distributed species may have partitioned its distribution in the relatively near past and adapted to various environments, in which the dominant pollinators were different, and that the local races may then have diverged from each other after they were isolated.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 325–341.     

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 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.     

Uncovering tropical diversity: six sympatric cryptic species of Blepharoneura (Diptera: Tephritidae) in flowers of Gurania spinulosa (Cucurbitaceae) in eastern Ecuador

Diversification of phytophagous insects is often associated with changes in the use of host taxa and host parts. We focus on a group of newly discovered Neotropical tephritids in the genus Blepharoneura , and report the discovery of an extraordinary number of sympatric, morphologically cryptic species, all feeding as larvae on calyces of flowers of a single functionally dioecious and highly sexually dimorphic host species ( Gurania spinulosa ) in eastern Ecuador. Molecular analyses of the mitochondrial cytochrome oxidase-I gene from flies reared from flowers of G. spinulosa reveal six distinct haplotype groups that differ by 7.2–10.1% bp (uncorrected pairwise distances; N  = 624 bp). Haplotype groups correspond to six distinct and well-supported clades. Members of five clades specialize on the calyces of flowers of a particular sex: three clades comprise male flower specialists; two clades comprise female flower specialists; the sixth clade comprises generalists reared from male and female flowers. The six clades occupy significantly different morphological spaces defined by wing pigmentation patterns; however, diagnostic morphological characters were not discovered. Behavioural observations suggest specific courtship behaviours may play a role in maintaining reproductive isolation among sympatric species. Journal compilation  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 779–797. No claim to original US government works.     

Partial self‐incompatibility in the polyploid endemic species Scalesia affinis (Asteraceae) from the Galápagos: remnants of a self‐incompatibility system?

Different pollination treatments of capitula were used to examine the breeding system of individuals of the tetraploid endemic species Scalesia affinis from the Galápagos Islands. All types of crossings resulted in approximately 35 achenes per capitulum, but in actively and passively self-pollinated capitula these were mostly without embryos. Among self-pollinated individuals a large variation was found in the production of embryos. Some individuals failed completely to set filled achenes while others produced few or many. Additionally, we found a clear difference in female phenology of florets in self-pollinated capitula compared with florets in cross-pollinated capitula. Female florets in self-pollinated capitula remained receptive for longer time. These results suggest that Scalesia affinis is partly self-incompatible. Outcrossing is assured by the endemic carpenter bee, Xylocopa darwini , which proved to be an important pollinator of Scalesia affinis . Nevertheless, geitonogamy seemed to be considerable in the focal population, for which reason open pollinated capitula produced fewer achenes than controlled outcrossed capitula.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 142 , 93–101.     

Cytotypes of Andropogon gerardii Vitman (Poaceae): fertility and reproduction of aneuploids

In many North American prairies, populations of Andropogon gerardii Vitman (Poaceae) are composed of hexaploid and enneaploid cytotypes (2 n  = 60, 90), with intermediates occurring occasionally. Under controlled pollination, the two common cytotypes can be crossed, producing progeny with a range of chromosome numbers. In an investigation of fertility and compatibilities of intermediate cytotypes, individuals with chromosome numbers between 60 and 90 were crossed with each other, with the 2 n  = 60 and 90 cytotypes, and with South American Andropogon species having 60 chromosomes. Regardless of cytotype, all A. gerardii plants had some fertility and virtually all crosses produced seeds. Cytotype is only partially predictive of fertility. Inter-specific hybrids between A. gerardii and South American hexaploid species were vigorous but sterile. Gene flow in natural A. gerardii populations of mixed cytotype probably involves plants of all cytotypes.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 141 , 95–103.