Floral ecology of Oreocharis acaulis (Gesneriaceae): An exceptional case of “preanthetic” protogyny combined with approach herkogamy

Protogyny is supposed to represent the ancestral form of dichogamy in the angiosperms, but is rare in advanced groups such as the Asteridae, in which protandry prevails by far. Here we report on an unusual form of protogyny combined with herkogamy in a Chinese species of Gesneriaceae (Asteridae–Lamiales): Oreocharis acaulis (formerly Opithandra acaulis). This is characterized by a conspicuous protrusion of the style from the flower bud and the stigma becoming receptive before corolla opening (female-only stage; preanthetic protogyny) and both sexes staying functional during anthesis (hermaphroditic stage), with the stigma presented above the anther level (approach herkogamy). The plants studied were found to be self-compatible, but autonomous self-pollination and apomixis were not observed. Successful pollination was found to depend fully on the presence of insect pollinators (Bombus sp.). The visiting frequency was higher in the hermaphroditic stage (in which also more nectar was produced) than in the female-only stage. The out-crossed flower buds opened earlier and had a shorter flowering period than selfed flowers. Similarly, the outcross-pollen germinated earlier and the pollen tube growth was faster than in self-pollen. Anthers, pistil and corolla of O. acaulis obviously form an integrative functional unit in which the elongated style plays a key role both in pollen-dispensing and pollen-deposition. The combination of preanthetic protogyny with herkogamy has probably arisen through selection for promoting out-crossing and prolonging the exposition time of the receptive stigma in order to capture a higher amount of pollen grains. This may be understood as a strategy to cope with scarcity of pollinators in the plants’ habitat.     

Floral traits mediate the vulnerability of aloes to pollen theft and inefficient pollination by bees

Background and Aims

Pollen-collecting bees are among the most important pollinators globally, but are also the most common pollen thieves and can significantly reduce plant reproduction. The pollination efficiency of pollen collectors depends on the frequency of their visits to female(-phase) flowers, contact with stigmas and deposition of pollen of sufficient quantity and quality to fertilize ovules. Here we investigate the relative importance of these components, and the hypothesis that floral and inflorescence characteristics mediate the pollination role of pollen collection by bees.

Methods

For ten Aloe species that differ extensively in floral and inflorescence traits, we experimentally excluded potential bird pollinators to quantify the contributions of insect visitors to pollen removal, pollen deposition and seed production. We measured corolla width and depth to determine nectar accessibility, and the phenology of anther dehiscence and stigma receptivity to quantify herkogamy and dichogamy. Further, we compiled all published bird-exclusion studies of aloes, and compared insect pollination success with floral morphology.

Key Results

Species varied from exclusively insect pollinated, to exclusively bird pollinated but subject to extensive pollen theft by insects. Nectar inaccessibility and strong dichogamy inhibited pollination by pollen-collecting bees by discouraging visits to female-phase (i.e. pollenless) flowers. For species with large inflorescences of pollen-rich flowers, pollen collectors successfully deposited pollen, but of such low quality (probably self-pollen) that they made almost no contribution to seed set. Indeed, considering all published bird-exclusion studies (17 species in total), insect pollination efficiency varied significantly with floral shape.

Conclusions

Species-specific floral and inflorescence characteristics, especially nectar accessibility and dichogamy, control the efficiency of pollen-collecting bees as pollinators of aloes.     

A preliminary study on pollination biology of Omphalogramma souliei Franch. (Primulaceae), a species endemic to China

The pollination biology of Omphalogramma souliei Franch., a species endemic to southwestern China, was investigated. Floral phenology, flower visitors, pollen/ovule ratio, attractants and rewards to the visitors were observed, measured, and recorded. Bagging experiments to exclude pollinators were carried out in the wild for two years. Our results revealed five important aspects of the reproductive biology of Omphalogramma souliei. 1) The pollen-ovule ratio was 1748±233. The breeding system was self-compatible, with facultative xenogamy. 2) The pollination syndrome is entomophily, and this species could not be pollinated by wind if the pollinators were unavailable. 3) Six insect species were observed visiting the flowers of Omphalogramma souliei in the wild, of them, three species of hymenoptera, Lasioglossum sp., Heriades parvula Cockerell and Micrapis florae Fabricius, are the principal floral visitors and effective pollinators. 4) The visual attractants to the visitors are floral color and shape, the large yellow anthers, and the rewards for visitors are pollen and nectar. 5) Cleistogamy may also occur, since the anthers of some flowers dehisced before opening of the corolla. The results of floral biology and pollination characters suggest that xenogamy predominated and autogamy played an assistant role in the evolution of reproduction and breeding system of O. souliei.     

High specialisation in the pollination system of Mandevilla tenuifolia (J.C. Mikan) Woodson (Apocynaceae) drives the effectiveness of butterflies as pollinators

Butterfly pollination in the tropics is considered somewhat effective or solely effective in a few plant species. In the present study, we tested the hypothesis that Mandevilla tenuifolia (Apocynaceae), which has floral attributes associated with psychophily, has strategies adapted to pollination by butterflies, restricting other floral visitors and making these insects act as efficient pollinators. We analysed the floral and reproductive biology of M. tenuifolia, as well as the frequency and efficiency of its flower visitors. M. tenuifolia is an herb whose flowers have strong herkogamy and secondary pollen presentation on the style head, which corresponds to 60.4% of pollen on the anthers. Flower longevity and the long period of receptivity of the stigmatic region associated with the large amount of pollen removed in the first visits suggest that flowers remain functionally female during part of anthesis. Butterflies, mainly of the families Nymphalidae and Pieridae, are the only pollinators of M. tenuifolia. Despite being self‐compatible, M. tenuifolia depends on biotic vectors for fruit production. A non‐significant difference in fruit set between controlled treatments and natural conditions suggests that the pollinators are efficient. The inclination resulting from the landing of butterflies on flowers, together with flower morphology, guiding the insect proboscis inside the floral tube, as well as the frequency and efficiency of butterfly visits, are evidence of the close relationship between butterflies and M. tenuifolia, and also of the efficiency of these insects as pollinators.     

The relative strength of different floral visitors driving floral evolution within a <Emphasis Type="Italic">Primula secundiflora</Emphasis> population

Floral visitor assemblages within plant populations are usually composed of different visitors, and the relative abundance of these visitors also varies. Therefore, identifying the relative strength of these floral visitors driving floral evolution within the population is an important step in predicting the evolutionary trajectory of floral traits. Using supplemental hand pollination and nectar-robbing exclusion treatments, we experimentally identified the relative strengths of legitimate pollinators (that visit flowers through the corolla tube entrance) and nectar robbers (that visit flowers by biting a hole in the corolla tube or using an existing hole) driving floral evolution within the Primula secundiflora population. We also estimated legitimate pollinator- and nectar robber-mediated selection separately for pin and thrum flowers. Both legitimate pollinators and nectar robbers mediated selection on pollination efficiency traits in P. secundiflora population. Legitimate pollinators mediated selection for wider corolla tubes, whereas nectar robbers mediated selection for longer corolla tubes. In addition, nectar robber-mediated selection on corolla tube length marginally varied between the pin and thrum flowers. Nectar robber mediated selection for longer corolla tube length in the pin flowers not in the thrum flowers. These results indicate that legitimate pollinators and nectar robbers within a population can drive differential evolutionary trajectories of floral traits.     

Nectary tracks as pollinator manipulators: The pollination ecology of Swertia bimaculata (Gentianaceae)

Floral nectaries are closely associated with biotic pollination, and the nectar produced by corolla nectaries is generally enclosed in floral structures. Although some Swertia spp. (Gentianaceae), including S. bimaculata, evolved a peculiar form of corolla nectaries (known as “gland patches”) arranged in a conspicuous ring on the rotate corolla and that completely expose their nectar, little is known about the pollination of these plants. Two hypotheses were made concerning the possible effects of gland patches: visual attraction and visitor manipulation. The floral traits, mating system, and insect pollination of S. bimaculata were examined, and the pollination effects of gland patches were evaluated. A comparative study was made using Swertia kouitchensis, a species with fimbriate nectaries. Swertia bimaculata flowers were protandrous, with obvious stamen movement leading to herkogamy in the female phase and to a significant reduction in nectary–anther distance. The species is strongly entomophilous and facultatively xenogamous. The daily reward provided per flower decreased significantly after the male phase. The most effective pollinators were large dipterans, and the visiting proportion of Diptera was significantly higher in S. bimaculata than in S. kouitchensis. Most visitors performed “circling behavior” in S. bimaculata flowers. Removing or blocking the nectaries caused no reduction in visiting frequency but a significant reduction in visit duration, interrupting the circling behavior. The circling behavior was encouraged by nectar abundance and promoted pollen dispersal. Visitor species with small body size had little chance to contact the anthers or stigma, revealing a filtration effect exerted by the floral design. These results rejected the “visual attraction” hypothesis and supported the “visitor manipulation” hypothesis. The nectary whorl within a flower acted like a ring‐shaped track that urged nectar foragers to circle on the corolla, making pollination in S. bimaculata flowers more orderly and selective than that in classically generalist flowers.     

Interaction between oil-collecting bees and seven species of Plantaginaceae

Oil-bee/oil-flower mutualism evolved through multiple gains and losses of the ability to produce floral oil in plants and to collect it in bees. Around 2000 plant species are known to produce floral oils that are collected by roughly 450 bee species, which use them for the construction of nests and for the larval food. The Plantaginaceae contain several Neotropical species that produce floral oils, the main reward offered by these plants. In the genera Angelonia, Basistemon, Monopera and Monttea, mainly associated with Centris bees, the floral oil is produced in trichomes that are located in the inner corolla. The pollinators of a few species in this neotropical clade of Plantaginaceae are known, and the role of flower morphology as well as the requirements from pollinators and the role of other groups of bees in the pollination of these flowers remains unclear. In this paper we provide a list of the flower visitors of seven Plantaginaceae species (six Angelonia species and Basistemon silvaticus) analyzing their behavior to highlight the legitimate pollinators and illustrating little known aspects of flower morphology and oil-collecting apparatuses of the bees. Two general morphological patterns were observed in the Angelonia flowers: deep corolla tube with short lobes, and short corolla tube with long lobes. Corolla tubes of different length result in pollen adherence to different parts of the insect body. The six Angelonia species and B. silvaticus flowers were visited by 25 oil-collecting bee species (10 Centris, 11 Tapinotaspidini and 4 Tetrapedia species), the majority acting as legitimate visitors. The flowers were also visited by illegitimate bee pollinators, which collected pollen but do not transfer it to the female organ. Specialized collectors of Plantaginaceae floral oils present modifications on the first pair of legs, mainly in the basitarsi but also extended to the tarsomeres. The new records of Tapinotaspidini and Centridini species acting as specialized pollinators of Plantaginaceae suggest that there is a geographic variation in the pollinators of the same plant species, and that the evolutionary scenario of the historical relationships between oil-collecting bees and floral oil producing plants is more complex than previously considered.     

Pollination biology of the hexaploid self‐compatible species Turnera velutina (Passifloraceae)

• The evolution of monomorphisms from heterostylous ancestors has been related to the presence of homostyly and the loss of self‐incompatibility, allowing the occurrence of selfing, which could be advantageous under pollinator limitation. However, flowers of some monomorphic species show herkogamy, attraction and rewarding traits that presumably favour cross‐pollination and/or a mixed mating system. This study evaluated the contributions of pollinators, breeding system and floral traits to the reproduction of Turnera velutina, a herkogamous monomorphic species.
• Floral visitors and frequency of visits were recorded, controlled hand cross‐pollinations were conducted under greenhouse and natural conditions, and individual variation in floral traits was characterised to determine their contribution to seed production.
• Apis mellifera was the most frequent floral visitor. Flowers presented approach herkogamy, high variation in nectar features, and a positive correlation of floral length with nectar volume and sugar concentration. Seed production did not differ between manual self‐ and cross‐pollinations, controls or open cross‐pollinations, but autonomous self‐pollination produced, on average, 82.74% fewer seeds than the other forms, irrespective of the level of herkogamy.
• Differences in seed production among autonomous self‐pollination and other treatments showed that T. velutina flowers depend on insect pollination for reproduction, and that approach herkogamy drastically reduced seed production in the absence of pollen vectors. The lack of differences in seed production from manual cross‐ and self‐pollinations suggests the possible presence of a mixed mating system in the studied population. Overall, this species was possibly derived from a distylous ancestor but appears fully capable of outcrossing despite being monomorphic.

     

Floral biology of Eriope blanchetii (Lamiaceae) in coastal sand dunes of NE Brazil

Abstract The floral biology of the sand dune shrub Eriope blanchetii (Benth) Harley was investigated in a wild population located within an environment protection area near Salvador, NE Brazil. Inflorescence and flower development were monitored, and the reproductive biology was assessed. Inflorescences are terminal panicles, each bearing from one to 38 small, zygomorphic flowers. The duration of an inflorescence is about 2 months, with few new flowers each day. The rewards to visitors are pollen and nectar, the latter being produced in small quantities at the corolla base, near the stylopodium. Three sequential phases of flower development were identified, based on colour changes, pollen and nectar availability, and stigmatic receptivity. Anthesis takes place throughout the day within each plant, and flowers are strongly protandrous. Flowers are short‐lived, with individual variations of 7–30 h until corolla abscission. This variation is probably associated to a post‐pollinating response, which reduces the length of the female phase and could be advantageous for the economy of nectar production and for increased efficient pollination of the remaining flowers on a plant. The results of the pollination tests (apomixis, spontaneous and manual autogamy, manual cross‐pollination, and control) reinforced the role of pollinators for the reproductive success of E. blanchetii, given that the production of fruits from spontaneous pollination is unlikely to be resulting from protandry and given the morphological floral features. Taken together, the morphological and physiological aspects of E. blanchetii floral biology favour cross‐pollination, and it is likely that most of the fruits in nature are produced by outcrossing.     

Pollinator directionality as a response to nectar gradient: promoting outcrossing while avoiding geitonogamy

Plants with multiple flowers could be prone to autonomous self‐pollination and insect‐mediated geitonogamy, but physiological and ecological features have evolved preventing costs related to autogamy. We studied the rare perennial herb Dictamnus albus as a model plant, with the aim of describing the plant–pollinator system from both plant and pollinator perspectives and analysing features that promote outcrossing in an entomophilous species. The breeding system and reproductive success of D. albus were investigated in experimental and natural conditions, showing that it is potentially self‐compatible, but only intra‐inflorescence insect‐mediated selfing is possible. Nectar analysis showed gender‐biased production towards the female phase, which follows the male phase, and during flowering, full blooming is found in flowers at the bottom of the raceme. Among a wide spectrum of insect visitors, three genera (Bombus, Apis, Megachile) were found to be principal pollinators. A study of insect behaviour showed a tendency towards bottom‐to‐top flights for the most important pollinators Bombus spp. and Apis mellifera: upward movements on the racemes could be explained by foraging behaviour, from more to less rewarding flowers. In accordance with the ‘declining reward hypothesis’, bumblebees and honeybees leave the plant when gain of reward is low, after which few flowers are visited, reducing the chance of self‐pollen transfer among flowers. Intra‐flower self‐pollination is prevented in D. albus by protandry and herkogamy, while the nectar‐induced sequential pattern of pollinator visits avoids geitonogamy and tends to maximise pollen export, promoting outcrossing. All these features for preventing selfing benefit plant fitness and population genetic structure.     

宁夏枸杞的花粉呈现式样及交配系统研究北大核心CSCD

被子植物的花回馈、雌雄蕊时空分离特征和花粉呈现式样等花部特征及传粉者效率会影响雄性适合度和有性繁殖过程。宁夏枸杞(Lycium barbarum)是中国宁夏、新疆、内蒙等干旱和半干旱地区分布的特有种。该研究对新疆喀什地区宁夏枸杞自然种群的花部综合征、花粉呈现式样、花回馈、传粉者行为与交配方式的关系进行观察及统计分析,以探讨其花粉逐步呈现的适应性及其在提高雌雄繁殖过程中的意义。结果表明:(1)宁夏枸杞的单花寿命为(4.07±0.15) d,而雄性持续时间(0.07±0.01 d)比雌性持续时间短(4±0.01 d);花寿命内雌蕊长度比雄蕊长,属柱头探出式异位类型;花粉呈现式样为不完全逐步呈现。(2)花寿命不同阶段花回馈间存在显著差异。(3)意大利蜜蜂(Apis mellifera)、熊蜂(Bombus sp.)、食蚜蝇(Syrphidae sp.)是宁夏枸杞在自然居群的主要访花者,其中熊蜂和食蚜蝇是主要传粉者,但传粉者效率低,属于高移出低沉积类型。(4)宁夏枸杞的花粉胚珠比(2 448.11±448.32)及授粉实验结果均表现出兼性异交特征;自发自交及人工自花授粉花的座果率及结籽率很低,属于自交不亲和类型;自然传粉花的座果率及结籽率比人工去雄异花低,存在其较高的花粉限制(40.71%)。研究发现,宁夏枸杞花部综合征表现出雌雄异位和花粉不完全逐步呈现式样,这是避免雌雄功能及雄蕊各花药间的干扰、减少花粉同步移出及保障其雄性适合度的有效途径,但自然居群的传粉者种类限制、传粉效率低以及自交不亲性是导致宁夏枸杞花粉限制及降低雌性繁殖成功的主要原因。     

Distyly and sequential pollinators of Psychotria nuda (Rubiaceae) in the Atlantic rain forest, Brazil

Reciprocal herkogamy is known to promote intermorph-pollination in distylous species, which are generally self- and intramorph-incompatible. Legitimate crossing rates are also influenced by pollinator foraging strategy, which determines most of the pollen flow in natural populations. This study reports on the floral morphology, compatibility relations and pollination biology of Psychotria nuda (Cham. and Schltdl.) Wawra in the Atlantic rain forest, southeastern Brazil, based on floral measurements, hand-pollination experiments and focal observation of floral visitors. It was found that P. nuda does not present an exactly reciprocal herkogamy, however, this morphological trait in P. nuda is as good as in most of Rubiaceae. Reproductive experiments showed compatibility relations similar to those frequently observed in distylous species. The hummingbirds Ramphodon naevius and females of Thalurania glaucopis were the main pollinators of P. nuda, presenting the traplining foraging strategy, which seems to maximize intermorph crosses in P. nuda flowers. These hummingbirds pollinated P. nuda flowers sequentially throughout the flowering period.     

The pollination ecology of Pedicularis rex subsp. lipkyana and P. rex subsp. rex (Orobanchaceae) from Sichuan, southwestern China

Pedicularis is one of few genera for which pollination ecology has been studied extensively. Although over half of the species of Pedicularis are found in the mountains of southwestern China, pollination ecology has been studied there on a few species only. The present paper reports pollination ecology of Pedicularis rex subsp. lipskyana and P. rex subsp. rex from Sichuan, southwestern China. The two subspecies are nectariferous, with sugar content 28% in P. rex lipskyana and 22% in P. rex, respectively. The flowers of the two subspecies are adapted to pollination by bumblebee workers. Bumblebees are the primary and effective pollinators although honeybees were also observed pollinating P. rex subsp. lipskyana at one studied population. Usually bumblebees entered the corolla tube from the right side in an upright or a nearly half-inverted position to imbibe nectar located at the base of the corolla tube. The stigma usually contacts the side region of the thorax and abdomen or occasionally directly contacted pollen loads, leading to pollination of flowers. Much less commonly, bumblebees foraged on flowers of P. rex subsp. rex in an inverted position for pollen, which pollinated flowers sternotribically. We suggest that pollination mechanism is closely associated with floral morphology. Some important differences were found from a previous study on P. rex in floral morphology and the primary pollination mechanism.     

Secondary pollen presentation: More than to increase pollen transfer precision

Pollination precision and efficiency have been deemed to be important driving forces in floral evolution. Herkogamy reduction is a main mechanism to increase pollination precision. Secondary pollen presentation (SPP), by which pollen is presented on other floral organs especially pistils, has been widely accepted as a special mechanism to increase pollen transfer precision through spatial reduction of the anther–stigma distance, that is, minimized herkogamy. This overlooks a potential driving force, that is expanding the pollination niche through converting pollen thieves and nectar robbers into effective pollinators. We selected two species as study models with typical pistillate SPP, Pavetta hongkongensis Bremek. (Rubiaceae) and Scaevola taccada (Gaertn.) Roxb. (Goodeniaceae). In both species, two distinct pollinator functional groups were recognized. Short-tongued bees and flies fed on pollen on stigmas but also stole pollen from anthers and robbed nectar, whereas long-tongued hawkmoths and butterflies only collected nectar. Emasculation had no influence on long-tongued pollinators, but significantly decreased the visitation frequency of short-tongued visitors and fruit set, compared to intact flowers, demonstrating short-tongued visitors did not effectively pollinate and acted merely as pollen thieves or nectar robbers when SPP was absent. Data from the two plant species clearly indicated pistillate SPP has additional adaptive advantages of converting ineffective visitors into pollinators and consequently widening the pollination niche, which could help plants overcome environmental stochasticity. Our results suggest that multiple selective forces drive the evolution of SPP and the minimization of herkogamy.     

Sexual differences in reproductive characters and pollinator attractiveness in gynodioecious Glechoma longituba (Lamiaceae)

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

Functional Significance of Interspecific Variation in Burmeistera Flower Morphology: Evidence from Nectar Bat Captures in Ecuador

What causes flowers to diverge? While a plant's primary pollinator should strongly influence floral phenotype, selective pressures may also be exerted by other flower visitors or competition with other plants for pollination. Species of the primarily bat‐pollinated genus Burmeistera (Campanulaceae) frequently cooccur, with up to four species in a given site, and broadly overlap in flowering phenology, typically flowering throughout the year. The genus displays extensive interspecific variation in floral morphology in the degree that the reproductive parts (anthers and stigma) are exserted outside of the corolla, and species can be roughly classified as either long or short‐exserted. I tested two hypotheses regarding the functional significance of such variation: (1) exsertion lengths correspond to pollination by bat species of different sizes; and (2) variation serves to partition pollinator's bodies spatially and thus reduces interspecific pollen transfer. I captured bats in Ecuador to evaluate the identity and location of the Burmeistera pollen they were carrying. Results show that exsertion does not correspond to specialization on different pollinators; different bat species carried pollen of both flower types just as frequently. In support of the second hypothesis, pollen from flowers of different exsertion lengths was found to occur on different regions of bats' heads. This may serve to reduce competition for pollination among coexisting Burmeistera.     

Deconstructing a floral phenotype: do pollinators select for corolla integration in Lavandula latifolia?

An experimental field study was undertaken to assess whether correlational selection generated by pollinators can account for observed phenotypic integration of the two corolla lips in the zygomorphic flowers of the insect‐pollinated Mediterranean shrub, Lavandula latifolia (Labiatae). The experiment consisted of manipulating the upper and lower corolla lips according to a two‐way factorial design with interaction, and involved the complete (lower lip) or extensive (distal two thirds of upper lip) excision of one or the two lips. Per‐flower male (proportion of pollen grains removed) and female (number of pollen tubes down the style) pollination success, and maternal fecundity (seed set), of experimental flowers were evaluated after exposure to natural pollination in the field. Artificially induced corolla variation had no significant effects on either male or female pollination success, and two aberrant floral morphologies, characterized by lack of corolla integration, had a maternal fecundity advantage over normal two‐lipped phenotypes. These results do not support a predominant role of correlational selection by pollinators in maintaining corolla integration in L. latifolia, but are instead consistent with the alternative view that integration is mainly the consequence of genetic and/or developmental factors.     

The pollination of the gynomonoecious Bdallophytum oxylepis (Cytinaceae,Malvales)

Bdallophytum oxylepis is a rare and endemic species belonging to the Cytinaceae family, a root holoparasitic plant in which most resources are allocated to attracting pollinators. This species is gynomonoecious with intraindividual variation in flower size and sex. Moreover, the flowers exhibit sapromyophilous traits, as do other species of Bdallophytum. Firstly, this study aimed to determine whether all floral morphs can form seeds and be pollen donors (in the case of bisexual flowers). Secondly, as this species has floral traits hypothesized to adapt to particular types of pollen vectors (carrion flies), we also studied the pollination of B. oxylepis to confirm whether the syndromes correspond to what occurs in nature. Through pollination treatments, we determined that all floral morphs are functional. By monitoring the inflorescences, we found that pollination is specialized in the studied population. Stingless bees performed pollination, as they have a high visitation rate, frequency, and constancy, and they are unique visitors that deposit pollen on the stigmas. Thus, they appear to be effective pollinators rather than carrion flies, as predicted by the syndrome. As shown here, animal–plant interaction studies can help establish a basis for conserving rare species such as holoparasites. Moreover, knowledge about the reproductive aspects of B. oxylepis reveals essential clues about its life cycle and role in maintaining native pollinators with economic and cultural value, such as stingless bees.     

Floral biology and mechanisms of spontaneous self‐pollination in five neotropical species of Gentianaceae

Cross‐ and self‐fertilization in angiosperms are regulated by several factors, and a knowledge of the mechanism and time of spontaneous self‐pollination offers opportunities for a better understanding of the evolution of mating systems and floral traits. The floral biology of five species of Gentianaceae found in high‐altitude neotropical grassland is presented, with emphasis on the mechanisms that promote spontaneous self‐pollination. A presumed floral Batesian mimicry system is suggested between the rare and rewardless Zygostigma australe and Calydorea campestris, a species of Iridaceae with pollen‐flowers, pollinated by syrphids and bees. The floral morphology of the other four gentian species points to three different pollination syndromes: melittophily, phalaenophily and ornithophily. However, with the exception of the nocturnal Helia oblongifolia, flowers are nectarless and appear to exhibit non‐model deceptive mechanisms, providing similar floral cues to some sympatric rewarding species with the same syndrome. The similar mechanism of spontaneous self‐pollination in Calolisianthus pedunculatus, Calolisianthus pendulus and H. oblongifolia (Helieae) is based on the stigmatic movements towards the anthers. Selfing is promoted by movements of the style/stigma and of the corolla in Deianira nervosa and Z. australe (Chironieae), respectively. The movements of stamens, style and stigma during anthesis seem to be the most common method of spontaneous self‐pollination in angiosperms. It is suggested that the evolution of delayed spontaneous self‐pollination would be more expected in those taxa with dichogamous flowers associated with herkogamy. Such a characteristic is frequent in long‐lived flowers of certain groups of Asteridae, which comprise most documented cases of autonomous selfing. Thus, the presence of dichogamy associated with herkogamy (which supposedly evolved as a result of selection to promote both separation of male and female functions and the efficient transfer of cross pollen) may be the first step in the adaptive evolution of delayed selfing to provide reproductive assurance. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 357–368.     

Confirmed mixed bird–insect pollination system of Scrophularia trifoliata L., a Tyrrhenian species with corolla spots

• Both bird and mixed vertebrate–insect (MVI) pollination systems are very rare in Europe and the Mediterranean region. Because MVI can ensure reproduction over a wider range of environmental conditions than when insects are the sole pollinators, under certain circumstances such systems are highly advantageous to plants. Here, we investigated the pollination and some reproductive traits of the Tyrrhenian Scrophularia trifoliata, the only species of the genus possessing two showy dark spots inside the corolla, for which MVI pollination system had been inferred on the basis of limited censuses.
• We conducted field experiments to study MVI pollination and some reproductive traits and elucidate the role of corolla spots, analysing their ultraviolet pattern, histology and pigments versus the rest of the corolla.
• The primary pollinators were wasps and passerine birds. Corolla spots absorb UV light, present abundant anthocyanins and are histologically identical to the rest of the corolla. Control flowers had higher visitation frequency than flowers without spots. S. trifoliata is self‐compatible, with efficient intrafloral protogyny and herkogamy that prevent self‐pollination but not geitonogamy.
• We confirmed the existence of a mixed bird–insect pollination system in S. trifoliata. This system is found in three other Scrophularia species with large, showy flowers – two Mediterranean (S. grandiflora and S. sambucifolia) and one Macaronesian (S. calliantha). Unlike those species, S. trifoliata has two large spots inside the corolla. These likely operate as nectar guides and their dark colouration is related to abundant anthocyanin content.