Dioecy inHonkenya peploides var.major (Caryophyllaceae)

Sexual difference and pollination system inHonkenya peploides var.major were investigated. The present analyses indicate that sex expression of this plant is functionally dioecious, rather than androdioecious, as described previously. Its flowers are largely pollinated by small bees, hover-flies, flies, and ants. Female flowers were morphologically characterized by conspicuously longer styles and smaller petals, and had no pollen grains, while male flowers had shorter styles, larger petals, and longer filaments, and produced viable pollen grains. Although the male flowers possess many ovules in an ovary, they set fruits at a very low frequency in natural conditions and did not produce fruits by pollination experiments. We suggest that the dioecy of this species has been derived from hermaphrodite through gynodioecy, and not directly from hermaphrodite.     

Stylar trimorphism in four functionally andromonoeciousProsopis species (Mimosaceae)

The reproductive system ofProsopis chilensis, P. pugionata, P. flexuosa, andP. torquata is described. Observations were made of floral morphology, stigmatic receptivity, pollen grain viability, and the nature of pollen reserves. Scanning electrone microscopy and statistical analysis were carried out. The results allow us to conclude that: 1) The studied species have three distinct floral morphs characterized by significantly different style lengths and, to a lesser extent, different stamen lengths; 2) style precocity found in all species does not indicate protogyny; 3) flowers with shortest styles are not receptive; 4) the pollen grains of all floral morphs showed high viability; 5) peroxidase is present in both the pollen and pistil; 6) viable pollen grains invariably have both starch and pollenkitt; 7) the studied species are andromonoecious.     

Dioecy in the endemic genusDendrocacalia (Compositae) on the Bonin (Ogasawara) Islands

Dendrocacalia crepidifolia Nakai (Compositae, Senecioneae), the only species of this arboreal genus endemic to Haha Island in the Bonin Islands, was found to be dioecious. Male flowers differ from female ones in having a stunted style (style in female exserted from corolla and deeply bifurcating) and anthers filled with fertile pollen (anthers in the female lacking pollen). The size of the corolla and number of florets per head were similar between male and female flowers. The crown area of this arboreal species was also similar in male and female plants. The sex ratio was 0.55 male, not significantly different from 0.5. Both sexes produced nectar of similar sugar concentration (ca. 50%). The flowers are pollinated by feral honeybees (Apis mellifera), but they are thought to have been pollinated by small, lesshairy, endemic solitary bees before honeybees were introduced and subsequently became the dominant bee species on the island. The evolution of dioecy ofDendrocacalia on the island is thought to stem from the deleterious effects of inbreeding that are inherent in plants with geitonogamy. The increased geitonogamy on the island has resulted from increased woodiness (i.e., increased number of flowers per plant) and the original dependence on endemic bee pollinators, which are now endangered.     

Interspecific pollen transfer as a mechanism of competition: Consequences of foreign pollen contamination for seed set in the alpine wildflower,Polemonium viscosum

Summary Earlier studies showed that under natural conditions foreign pollen receipt is correlated with loss of seed set in populations of P. viscosum. Here, we report on experimental pollinations using foreign pollen from two co-flowering species that share pollinators with P. viscosum. Experiments were designed to ascertain whether improper pollen transfer causes reduced seed set under controlled conditions and, if so, to determine the stage at which interference occurs. In flowers pre-treated by pollination with either Mertensia or Castilleja pollen, adherence of subsequently deposited conspecific pollen grains was unaffected. However, conspecific grains had significantly lower germination and ovule fertilization success in flowers receiving foreign pollen than in controls. These results suggest that pollinator infidelity in high alpine plant communities can reduce female reproductive success of P. viscosum by inhibiting the performance of conspecific pollen grains. Negative effects of Mertensia and Castilleja pollen were comparable despite large interspecific differences in pollen grain morphology. Accordingly, susceptibility to foreign pollen interference appears to be an intrinsic property of P. viscosum that is not dependent on the unique structural properties of pollen produced by competitive species.     

Pollination mechanisms in sixCampanula species (Campanulaceae)

Pollination mechanisms within the genusCampanula were studied. Tests were undertaken to examine whether in vitro culture of pollen grains can serve as a useful tool for understanding the self- and cross-pollination mechanisms among species. Characteristics of pollen germination were interpreted in relation to mating system and floral biology. Four annual species (Campanula kremeri, C. dichotoma, C. afra, C. lusitanica), and two perennial species (C. rotundifolia andC. persicifolia) were investigated. In the annual species pollen germinability is controlled by (1) the age of pollen and/or (2) in what position pollen is deposited around the style. Correlations were found between pollen germinability and mating system in three of the four annual species. No correlations were found either between germinability and age of pollen or position on the style in the perennial species. Pollen germinability reached its maximum in the middle of the male phase in all species, except forC. dichotoma, which had a decreasing germinability throughout anthesis. The germinability was lowest at the time of stigma receptivity for all species except forC. persicifolia, where the stigma did not develop as long as pollen remained on the style. The pollen collecting hairs and pollen removal have been found to play an important role controlling the stigma development, thus affecting self-pollination. This was especially pronounced inC. persicifolia. Further studies will be undertaken to elucidate factors influencing pollination within the genusCampanula.     

Reproductive biology ofCistus ladanifer (Cistaceae)

The phenology, major floral characteristics, fruiting levels, and breeding system ofCistus ladanifer L. (Cistaceae), a common western Mediterranean shrub species, were studied in a southern Spanish population. The white, large (64 mm in diameter) flowers of this shrub appear during spring (March–May) and produce abundant pollen and nectar. In the year of study, flowers lasted up to three days, during which they were visited by a diverse array of insects including beetles, flies, and bees. Hand-pollinations revealed that flowers do not set any seed unless cross pollen is applied to the stigma. Microscopical observations indicate that self pollen tubes grow down the stigma but invariably fail to induce fruit maturation. At the plant level, all estimates of fecundity investigated (number of seeds per capsule, proportion of ovules developing into seed, and proportion of flowers setting fruit) were highly dependent on nearest neighbour distance, with isolated plants setting as little as 0% fruit. In contrast, plants within a clump often transformed into fruit as much as 90% of the flowers. At the population level, seed output was estimated to range between 3,000 and 270,000 seeds per plant during 1991.     

Floral colour change in Pedicularis monbeigiana (Orobanchaceae)

We examined the effects of the retention of colour-changed flowers on long- and short-distance attractiveness of bumblebees and the likelihood of successive flower visits by bumblebees in Pedicularis monbeigiana. The lower lip changed colour with age from white to purple. Hand geitonogamous pollination significantly reduced seed production. No pollen limitation occurred in this species. Purple-phase flowers contributed minimally to pollinator attractiveness at long distance. The combination of less reproductive flowers with a lower amount of reward and floral colour change enabled plants to direct pollinators to reproductive, highly rewarding white flowers at close range. A high percentage of purple-phase flowers in an inflorescence was associated with a marked reduction in the frequency of successive flower visits to individual plants. We suggest floral colour change in P. monbeigiana may serve as a mechanism for enhancing inter-individual pollen transfer and reducing intra-individual pollen transfer.     

Dimorphic exine sculpturing in three distylous species ofLinum (Linaceae)

DistylousLinum grandiflorum, L. mucronatum, andL. pubescens have dimorphic pollen grains. In short-styled flowers the exine has monomorphic processes each with a ring of papillae. In long-styled flowers the exine has two types of processes: small processes terminating in a spinule and larger processes with a central spinule surrounded by a ring of spinuels, papillae or buttresses. The distylousLinum species of four different sections, in which morph-specific differences in the wall structure of stigmatic papillae have been reported, also exhibit exine dimorphism. The patterns of these dimorphisms are similar in all four sections in which distyly is present.     

The pollination biology of two species of Helicteres (Malvaceae) with different mechanisms of pollen deposition

Species of Helicteres are pollinated mainly by hummingbirds and bats. Most species pollinated by hummingbirds have a mechanism of depositing pollen on the top of the pollinator's head such as is shown in this work for Helicteres sacarolha. H. brevispira has an unusual mechanism of depositing pollen grains under the tail or on the abdomen of the hummingbirds. The top of the birds’ head may be considered an efficient place to transport pollen grains, because it is plain, easily accessible for deposition and donation of pollen and not easily accessible for grooming, while the tail is movable and inclined. Thus, H. brevispira pollinators may carry or transfer fewer amounts of pollen grains than H. sacarolha pollinators from one flower to another. If a large amount of pollen grains is lost, a higher quantity of flower or pollen has to be produced to guarantee reproductive success. Plants of H. brevispira set higher number of flowers and pollen grains per flower than H. sacarolha and have also higher rates of fruit and flower abortion. Thus, pollination efficiency of H. brevispira may be reached by high pollen and flower production. Flower change mechanism presented in this species may be also involved with the optimization of pollinator feeding and pollination efficiency.     

Heterostyly and pollen flow in Hypericum aegypticum (Guttiferae)

Distyly in Hypericum aegypticum is associated with a moderately strong incompatibility system. Pollen size is dimorphic and pin flowers produce more pollen grains than thrum flowers. A population studied in Morocco has plants with pin flowers and those with thrum flowers present in a 1: 1 ratio. In the field, stigmas of pin flowers receive 1.5 times as many pollen grains as those of thrum flowers. At least half the pollen grains in the pollen load on stigmas of both forms are incompatible grains originating from the same floral form. Although ample compatible pollen is received by stigmas of both forms to account for a full seed set, the overall pattern of pollen flow in the species does not fit the Darwinian ideal. In Hypericum , the unique occurrence of distyly in H. aegypticum, H. aciferum and H. russeggeri , the three species comprising section Adenotrias , and the derivative nature of these species within the genus, indicate that heterostyly has evolved within the genus and is not a primitive trait.     

Gender variation in Actinidia deliciosa,the kiwifruit

Summary Flower and fruit characters were measured in ten female, five male and five fruiting male selections of A. deliciosa var deliciosa (A. Chev) Liang and Ferguson. Flowers from female vines had functional pistils, which contained many ovules. Stamens appeared to be fully developed but produced only empty pollen grains. Flowers from male vines had functional stamens that produced high percentages of pollen grains with stainable cytoplasmic contents. Pistils did not contain ovules and were generally small with vestigial styles. Fruiting male vines had both staminate and bisexual flowers. Staminate flowers were similar to those found on strictly male vines. Bisexual flowers produced ovules and stainable pollen. Pistils were smaller than in pistillate flowers. Although the three flower sexes differed in style length, ovary dimensions and ovules per carpel, staminate and bisexual flowers were similar in number of flowers per inflorescence, stamen filament length, pollen stainability, inflorescence rachis length and carpel number, and differed from pistillate flowers in these characters. The three flower sexes had similar sepal and petal numbers. The fruit of fruiting males were considerably smaller than those of females. Low ovule number appears to be the major factor limiting fruit size in the fruiting males studied. Prospects for developing hermaphroditic kiwifruit cultivars through breeding are discussed.     

In-vitro development of ovules obtained after pollination of cotton (<Emphasis Type="Italic">Gossypium</Emphasis> spp) flowers with pollen from okra (<Emphasis Type="Italic">Abelmoschus esculentus L. Moench)</Emphasis>

The in vitro response of ovules obtained after pollination of cotton flowers with pollen from Abelmoschus esculentus was studied. For this, 492 cotton flowers from five G. hirsutum varieties, four G. barbadense varieties and 10 F1 interspecific hybrids, were pollinated with pollen from A. esculentus and 5,069 ovules were cultured in vitro. From the cultured ovules, 69 embryos were isolated and 16 of them grew into plants. However, only three of them survived after transplantation. Finally, one plant which originated from the interspecific cross (B403 × Acala Sindos) × A. esculentus reached maturity. The mature plant (Pa0) had no morphological traits from A. esculentus. On the contrary, traits from both cotton species were observed. The flowcytometric analysis of the Pa0 plant indicated that it was hypoaneuploid. Root tip chromosome counts of its offsprings revealed a progressive chromosome increase from the Pa1 to Pa4 generation. Plants with 52 chromosomes or hypoaneuploids with a lower level of chromosomes (46–51) could be isolated from the Pa4 generation. These plants exhibited morphological traits from both cotton species and they were fertile. No signs of A. esculentus morphological characteristics were observed in these plants. It was concluded that aneuploid partial interspecific cotton plants could be produced after pollination of cotton interspecific hybrids with pollen from A. esculentus and application of an in-ovule embryo rescue technique.     

In vitro induction of tetraploid in pomegranate (Punica granatum)

Tetraploid plants were obtained in pomegranate (Punica granatum L. var. `Nana') by colchicine treatment of shoots propagated in vitro. Shoots cultured on MS medium supplemented with 10 mg l^–1 colchicine, 1.0 mg l^–1 BA and 0.1 mg l^–1 NAA for 30 days produced tetraploids at a high frequency of 20%. No tetraploids were detected by treating the shoots in 5000 mg l^–1 colchicine for 114 h. Shoots treated by 5000 mg l^–1 colchicine for 96 h produced three morphological mutants with narrow leaves, which were later confirmed as mixoploids that separated into diploids and tetraploids after further subculture. In vitro tetraploid plants had shorter roots, wider and shorter leaves than the diploid ones. Tetraploid pomegranate plants grew and flowered normally in pots, but possessed flowers with increased diameter and decreased length compared to diploids. The number of pollen grains per anther was higher in tetraploids, but the viability of pollen decreased significantly.     

Competition between the oligolectic beePtilothrix plumata (Anthophoridae) and the flower closing beetlePristimerus calcaratus (Curculionidae) for floral resources ofPavonia cancellata (Malvaceae)

The flowers ofPavonia cancellata, a creeping ruderal half-shrub of northeastern Brazil, open synchronously at 6:00 h with all anthers already dehisced. The oligolectic beePtilothrix plumata was the most effective pollinator. During 90—180 min, female bees make up to 40 brief pollen collection trips to provision their brood cells. The pollen of about 40 flowers ofP. cancellata is needed to feed one bee larva. The most frequent flower visitors, however, are the specialized curculionid beetlesPristimerus calcaratus, which do not crosspollinate the flowers. They perforate the epidermis with their mouthparts, provoking dehydration, and then actively close the loose petals with their legs. Two hours after opening, half of the flowers had already been closed by the beetles. We interpret the fast, uninterrupted pollen foraging ofPtilothrix plumata bees as a strategy adapted to synchronous pollen presentation ofPavonia and to competition withPristimerus calcaratus: the female bees have to provision their brood cells before the beetles succeed in closing the flowers.     

Early in vitro flowering and seed production in culture in <Emphasis Type="Italic">Dendrobium</Emphasis> Chao Praya Smile (Orchidaceae)

Plantlets of Dendrobium Chao Praya Smile maintained in vitro were induced to flower, which produced viable seeds within about 11 months. A two-layer (Gelrite-solidified layer topped with a layer of liquid medium of the same volume and composition) culture system containing benzyladenine (BA) at 11.1 μM induced the highest percent of flowering (45%) in plantlets within 6 months from germination. The percentage of inflorescence induction was increased to 72% by pre-selecting morphologically normal seedlings prior to two-layer culture. Plantlets in culture produced both complete (developmentally normal but smaller than flowers of field grown plants) and incomplete flowers. Pollen and female reproductive organs of in vitro-developed complete flowers were morphologically and anatomically similar to flowers of field grown plants. In addition, 65% of the pollen grains derived from in vitro-developed flower were tetrad suggesting that regular meiosis occurred during microsporogenesis. The percentage of germination of pollen grains derived from in vitro-developed flowers and flowers of field grown plants, incubated on modified Knops’ medium for 8 days, were 18.2 and 52.8%, respectively. Despite a lower percentage of germination of the pollen grains derived from in vitro-developed flowers, flowers induced in culture could be self-pollinated and developed seedpods with viable seeds. Nearly 90% of these seeds developed into protocorms on germination in vitro. These seedlings were grown in culture and induced to flower in vitro again using the same procedure.     

Reproductive biology ofCaesalpinia calycina andC. pluviosa (Leguminosae) of the caatinga of north-eastern Brazil

The pollination biology, breeding system and fruiting success ofCaesalpinia calycina andC. pluviosa var.sanfranciscana were studied in caatinga vegetation in Bahia, NE Brazil. The principal pollinators for both species were carpenter bees.Caesalpinia calycina is andromonoecious but inC. pluviosa all flowers are hermaphrodite. InC. calycina all selfed flowers were abscised within 72 h despite rapid self-pollen tube growth to the ovary and ovule penetration. Prevention of selfing therefore seems to be controlled by a post-zygotic mechanism. Both species had very low fruit-set and it is suggested that this is at least in part due to geitonogamous pollinations with ovule penetration by self pollen tubes.     

Reproductive biology of Lactoris fernandeziana (Lactoridaceae)

Lactoris fernandeziana, monotypic in its family, is endemic to the cloud forests of Robinson Crusoe Island. Although there has been considerable study of the relationships of Lactoris, as a rare species and as a putative primitive paleoherb, little is known of its reproductive biology. Knowledge of the latter is essential for effective conservation programs. The species is gynomonoecious. The overall proportion of flowers is ∼1 female:1 hermaphrodite. The inconspicuous semipendulous green flowers, usually in mixed-gender inflorescences, do not produce rewards. Hermaphrodite flowers are herkogamous and protogynous. Pollen grains are shed from the extrorse anthers in permanent dry tetrads. There is a mean of 12879 tetrads per hermaphrodite flower. Both flower types bear an average of ∼18 ovules. The P/O (pollen/ovule) ratios imply facultative or obligate xenogamy, but hand pollinations show that Lactoris is self-compatible. No floral visitors were ever observed, but stigmata of open-pollinated flowers bore tetrads, and 64% of such styles had pollen tubes. Flowers enclosed in large mesh (1 mm) bags bore similar numbers of tetrads and pollen tubes. Thus, we conclude that Lactoris is anemophilous, a syndrome perhaps reflected by the P/O ratio. Low genetic diversity (isozymes and DNA) supports selfing and implies limited distance wind pollen dispersal. The small size of the island, the ± 1000 extant Lactoris plants, coupled with anemophily, self-compatibility, and pendant flower position, have yielded a geitonogamous system with high seed set and low genetic diversity. If inbreeding depression is expressed, it is in seed germination and seedling vigor, for Lactoris is very difficult to cultivate. For this species, effective conservation practices need to focus on habitat preservation and promotion of outcrossing.     

Pollen morphology and functional dioecy inSolanum (Solanaceae)

Dioecy has evolved independently several times in the large, mostly tropical genusSolanum. In all cases of dioecy inSolanum functionally male flowers have normal anthers, normal pollen and reduced stigmas while functionally female flowers have stigmas and anthers that appear normal but contain non-functional, usually inaperturate pollen. The inaperturate pollen has living cytoplasm, but apparently never germinates and it has been hypothesised that the pollen in these functionally female flowers is retained as a pollinator reward. Pollen morphology is compared in twelve of the thirteen known dioecious species ofSolanum, and some stages in the the development of inaperturate pollen in the anthers of functionally female flowers ofSolanum confertiseriatum of Western Ecuador are examined. Observations on the development and morphology of inaperturate pollen in functionally female flowers ofSolanum are related to hypotheses about the evolution of dioecy in the genus.     

Distyly and pollen dimorphism in<Emphasis Type="Italic"> Damnacanthus</Emphasis> (Rubiaceae)

We document distyly in Damnacanthus (Rubiaceae) and investigate pollen morphology in the genus. Within nine taxa in Japan (four species, four varieties and one form), five show distyly. Non-distylous taxa of Damnacanthus always have a long style and short stamens. We examined the pollen morphology of all taxa of Damnacanthus in Japan. The pollen grains of Damnacanthus are 3- to 5-orthocolporate or sometimes loxocolporate. Polymorphic pollen is sometimes observed even within a single flower. Pollen dimorphism is associated with distyly; pollen grains from short-styled (thrum) flowers are significantly larger than those from long-styled (pin) flowers, and the muri are smooth in pin flowers whereas the pollen grains of thrum flowers have minute granules on the top and/or on the sides. In non-distylous taxa, in which the style is longer than stamens, the muri are always provided with minute granules. Interestingly, the pollen grains with granules in the non-distylous taxa contrast with the pollen of the distylous taxa, because granulate pollen grains are found only in thrum flowers. Although Damnacanthus is a stenopalynous genus, the number of colpi is useful for delimiting taxa. Based on palynological characters, we conclude that Damnacanthus should be revised. Electronic Publication     

Phenotypic gender variation within inflorescences of the protogynous species Helleborus foetidus L. (Ranunculaceae)

In the protogynous species H. foetidus, I investigated if investment in sexual structures and seed set shows any trend with position in the flower-opening sequence. In four-flower inflorescences, stamen number decreased with flower position i.e. was highest for the earliest flower and lowest for the latest flower. Ovule number was significantly higher in the latest flower. Stamen and ovule number did not covary, indicating that there is no structural gender trade-off in this species. Seed set (i.e. percentage of ovules producing seed) did not differ between control plants and pollen-supplemented plants and the effect of pollen supplementation did not vary among positions. Seed set showed marginally significant differences between control plants and simulated-herbivory plants, but the effects of this treatment varied significantly among positions. Significant among-position variation in seed set was observed in the control plants but not the simulated-herbivory plants. Seed set of latest-opening flowers of simulated-herbivory plants was significantly higher than that of latest-opening flowers of control plants. H. foetidus support Brunet and Charlesworth's (1995) prediction that in plants with protogynous flowers, later-opening flowers should specialize as female flowers, at least under conditions of high resource availability.