Comparative floral morphometrics in day-flowering, night-flowering and self-pollinated Caryophylloideae (Agrostemma, Dianthus, Saponaria, Silene, and Vaccaria)

Morphological variation of flowers with different pollination modes was studied in 53 species representing five genera (Agrostemma, Dianthus, Saponaria, Silene s.l., Vaccaria) of the subfamily Caryophylloideae. All species were classified a priori as either diurnal, nocturnal, or selfing. Canonical discriminant analysis (CDA) of 13 floral characters revealed significant correlations between floral morphometry and pollination modes. A CDA of taxonomical groups represented with more than three species (Dianthus, and subgroups of Silene s.l.: Lychnis, Silene s.str., and Viscaria), revealed that the discrimination between these four taxa, based on the same floral characters, is also well supported. Main factors for the discrimination of the species with different pollination modes were characters that (a) define nectar accessibility (calyx length, calyx tooth length), (b) are related to the positioning of anthers and stigmatic areas in relation to pollinators and (c) are important for the visual attractiveness of flowers (plate width). The functional distance between the nectar source (anthophore base) and contact zone with pollinators (style tips), given as the sum of anthophore length, ovary length, and style length (hence called AOS-complex) is better correlated with the calyx length than the single characters. Further, the total AOS-complex length differs significantly between pollination modes suggesting that these characters form a functionally linked complex that is related to the pollen placement on, and stigma contact with, the pollinator's body. However, the contribution of anthophore and style length to the total AOS-complex differed significantly between Silene s.l. and other taxa indicating that the taxonomic groups follow different evolutionary ways for the construction of the functionally linked AOS-complex.     

Pollination and breeding system of Melochia tomentosa L. (Malvaceae), a keystone floral resource in the Brazilian Caatinga

The main goals of the present paper were to investigate the floral biology and the breeding system of Melochia tomentosa in a semi-arid region in Brazil, comparing the role of Apis mellifera with other native pollinators, and to discuss the importance of this plant species as a floral resource for the local fauna in maintaining different guilds of specialized pollinators in the Caatinga. M. tomentosa is very common in Caatinga areas and blooms year-round with two flowering peaks, one in the wet and another in the dry period. The pink, bright-colored flowers are distylous and both morphs are homogamous. The trichomatic nectary is located on the inner surface of the connate sepals, and the nectar (ca. 7 μl) is accumulated in the space between the corolla and the calyx. Nectar sugar concentration reaches an average of 28%. The results of controlled pollination experiments show that M. tomentosa is self-incompatible. Pollen viability varies from 94% to 98%. In spite of being visited by several pollen vectors, flower attributes of M. tomentosa point to melittophily, and A. mellifera was the most frequent visitor and the principal pollinator. Although honeybees are exotic, severely competing with native pollinators, they are important together with other native bees, like Centris and Xylocopa species, for the fruit set of M. tomentosa. This species represents a keystone floral resource favoring the maintenance of many species of bees, butterflies and hummingbirds through the year in this deciduous tropical dry forest.     

Oriole pollination ofErythrina breviflora (Leguminosae): Evidence for a polytypic view of ornithophily

Erythrina breviflora is visited by large numbers of passerine birds of which orioles (Icterus: Icteridae) are the primary pollinators. The flowers produce large quantities of nectar but they are rarely visited by hummingbirds. Inflorescence and floral morphology, and low levels of sucrose in the nectar probably explain the rarity of foraging hummingbirds. A comparison of Old WorldErythrina and their pollinators with New World species pollinated by orioles and hummingbirds suggests that parallel evolution has occurred. When the comparison is expanded to include other species pollinated by orioles, it is clear that various New WorldIcteridae, Thraupidae, etc. are ecological equivalents of Old WorldOriolidae, Pycnonotidae, Sturnidae, etc. and that flowers pollinated by these birds have similar characteristics.     

Honeydew feeding in the solitary bee Osmia bicornis as affected by aphid species and nectar availability

Like honey bees (Apis mellifera), non-Apis bees could exploit honeydew as a carbohydrate source. In addition to providing carbohydrates, this may expose them to potentially harmful plant products secreted in honeydew. However, knowledge on honeydew feeding by solitary bees is very scarce. Here we determine whether the polylectic solitary bee Osmia bicornis (=O. rufa) collects honeydew under semi-field conditions, and whether this is affected by aphid species and presence of floral nectar. Bees were provided with oilseed rape plants containing flowers and/or colonies of either Myzus persicae or Brevicoryne brassicae. We used the total sugar level of the bee crop as a measure of the individual's nutritional state and the oligosaccharide erlose as indicator for honeydew consumption. Erlose was present in honeydews from both aphid species, while absent in oilseed rape nectar, nor being synthesized by O. bicornis. When bees were confined to a single honeydew type as the only carbohydrate source, consumption of M. persicae honeydew was confirmed for 47% of the bees and consumption of B. brassicae honeydew for only 3%. Increased mortality in the latter treatment provided further evidence that B. brassicae honeydew is an unsuitable food source for O. bicornis. All bees that were given the choice between honeydew and floral nectar showed significantly increased total sugar levels. However, the fact that no erlose was detected in these bees indicates that honeydew was not consumed when suitable floral nectar was available. This study demonstrates that honeydew exploitation by O. bicornis is dependent on honeydew type and the presence of floral nectar.     

Pollination by deceit,floral sex ratios and seed set in dioecious Rubus chamaemorus L.

Summary Male and female flowers of the dioecious perennial herb Rubus chamaemorus L. are similar in general appearance. However, female flowers are somewhat smaller, do not produce any pollen, and contain very small amounts of nectar. Syrphids and bumblebees, which are important pollinators of R. chamaemorus, showed a strong preference for male flowers. Male flowers were also less often rejected by flower visitors than were female flowers, and two different groups of syrphid species stayed longer in male than in female flowers. These observations suggest that female flowers of R. chamaemorus attract pollinators by deceit.Hand-pollination experiments indicated that pollen availability limited seed production of R. chamaemorus in female dominated habitats but not in areas with an equal floral sex ratio. We suggest that the relative importance of factors limiting female reproductive success is not constant, but is influenced by the floral sex ratio of the population. This should apply also to other dioecious species that show variable sex ratios on either a local or regional scale.     

Effect of nectar supplementation on male and female components of pollination success in the deceptive orchid Dactylorhiza sambucina

Many orchids lack floral nectar rewards and therefore rely on deception to attract pollinators. To determine the effect that a mutation for nectar production would have on overall pollination success of the deceptive orchid Dactylorhiza sambucina, we recorded pollen deposition and removal in flowers of plants that had either been supplemented with an artificial nectar solution or left unmanipulated as controls. Nectar supplementation resulted in significant increases in the proportion of flowers pollinated, regardless of morph colour and the density of plants supplemented in the population. However, nectar supplementation had a significant positive effect on pollinaria removal only for the yellow morph in one experiment in which a low proportion of plants were supplemented. Thus a mutation for nectar production would have a positive effect on overall pollination success in D. sambucina, particularly the female component. The observed patterns are discussed in relation to other factors, such as cross-pollination and the reallocation of nectar resources for other plant functions, which are traditionally considered to shape the rewardless strategies of orchids.     

Nectary structure and nectar presentation in Aloe castanea and A. greatheadii var. davyana (Asphodelaceae)

This paper deals with the nectary structure and nectar presentation of two species belonging to different sections of the genus Aloe: A. castanea (Anguialoe) and A. greatheadii var. davyana (Pictae). The development of the nectary was studied by means of bright field and fluorescence light microscopy and scanning electron microscopy (SEM) in three flower stages (young, intermediate, old). Both species have septal nectaries. In A. castanea, a subsidiary tissue, not present in A. greatheadii var. davyana, was found beneath the nectary epithelium. This tissue accumulated starch that was hydrolyzed during secretion. Starch was slightly accumulated around the nectary in A. greatheadii var. davyana. The distribution of chlorophyll in the ovary was also different in the two species. These anatomical differences are not, however, correlated with greater nectar production in A. castanea. In this species, the nectary seems to degenerate after secretion, while in A. greatheadii var. davyana no sign of degeneration was observed. Differences in nectar presentation among the two species may account for different pollinators visiting their flowers.     

3种雌雄异熟樟科植物开花动态的比较研究

为了解樟科植物雌雄异熟的繁育系统特点,对3种樟科植物阴香(Cinnamomum burmannii)、紫楠(Phoebe sheareri)和浙江楠(Phoebe chekiangensis)雌雄异熟花的开花动态进行了比较研究.结果表明,3种植物雌性功能期的开始时间、雌性功能期和雄性功能期的时间分配有差异.3种植物的主...     

Pollination-related characteristics in the mimosoid legumeAcacia terminalis (Leguminosae)

Intraspecific variation has been found for several pollination-related characteristics in two isolated populations of the self-incompatible treeAcacia terminalis: floral characteristics including colour and flowering time; style length; size and colour of extrafloral nectaries on the leaf petioles; chemical components of the extrafloral nectar; different taxa of bee pollinators; and frequency differences in bird pollinators. These differences possibly reflect the evolution of two different pollination syndromes within this species.     

Nectar by day and night:Siphocampylus sulfureus (Lobeliaceae) pollinated by hummingbirds and bats

Most species of the neotropical genusSiphocampylus are believed to be bird-pollinated. The pollination biology ofSiphocampylus sulfureus was studied in a montane region in SE Brazil. This species has features intermediate between ornithophilous and chiropterophilous syndromes: it presents a striking combination of yellowish flowers with strong odour (chiropterophilous features), and diurnal anthesis and sucrose-dominated nectar (ornithophilous features). Major pollinators were hummingbirds by day, and a phyllostomid bat by night.Siphocampylus sulfureus may be viewed as a recent derivate from the presumed ornithophilous stock within sect.Macrosiphon, and thus benefits from the activity of both diurnal and nocturnal vertebrate pollinators.Dedicated to DrIlse Silberbauer-Gottsberger and Prof. DrGerhard Gottsberger for their pioneer contribution to floral biology in Brazil.     

Nectary structure and nectar characteristics in someBignoniaceae

The nectary structure and chemical nectar composition of 15 species belonging to 12 genera ofBignoniaceae are analyzed. All taxa bear a conspicuous nuptial nectary surrounding the ovary base. The secretory tissue is mostly supplied by phloem branches. The stomata are located in the middle and upper part of the nectary epidermis with an homogeneous distribution. The nuptial nectary is proportionally large in relation to the ovary (15–30%), disregarding the nectary volume. Most species have extranuptial nectaries in both inner and outer surfaces of the calyx. Both kinds of nectaries lack a vascular tissue that straightly supplies them. Nuptial nectar concentration (wt/wt) ranges from 19 to 68%. Sugars and amino acids are found in all species. Half of the species have hexose predominant nectars, the remaining sucrose predominant. Phenols are detected in only three species, whereas reducing acids exclusively inTecoma stans. Alkaloids and lipids were never detected. Extranuptial nectar chemical composition is analyzed in two species:Dolichandra cynanchoides andPodranea ricasoliana. Bees constitute the main flower visitors of the species studied whereas hummingbirds were seen visiting three species. A correlation analysis is performed with the data obtained. There are a few significant correlations which indicate a parallel increase of three parameters: the longer the flower length, the more voluminous the nectary and the higher stomata number, independently of the floral biotype. Phenograms are obtained using 24 floral characters including nectary and nectar data. The clusters obtained do not reflect taxonomic relationships but are useful in the understanding of animal-plant interactions when the flower biotype is considered.This paper is based on a chapter of a doctoral thesis presented at the University of Córdoba (Argentina).     

The movement patterns of carpenter beesXylocopa micans and bumblebeesBombus pennsylvanicus onPontederia cordata inflorescences

The movement patterns of carpenter bees (Xylocopa micans) and bumblebees (Bombus pennsylvanicus) foraging for nectar on vertical inflorescences ofPontederia cordata were studied near Miami, Florida. The floral biology ofP. cordata is unique in several ways: (a) many short-lived flowers per inflorescence, (b) constant nectar production throughout the life span of each flower, and (c) abscence of vertical patterning of nectar and age of flowers. Inflorescences ranged between 3.5 and 15.8 cm long and had between 9 and 55 open flowers. Both carpenter bees and bumblebees arrived mostly on the bottom third of the inflorescence and left after visiting flowers on the top third of the inflorescence. The departure position from the inflorescence was higher up than observed in studies of other insect pollinators foraging on other speces of plants. This pattern of departure probably occurs in the absence of a vertical gradient of nectar or floral morphology.     

Contrasting breeding systems in twoEriotheca (Bombacaceae) species of the Brazilian cerrados

The pollination biology and breeding systems ofEriotheca pubescens andE. gracilipes have been studied. These two species occur as trees in cerrado vegetation, the neotropical savannas of Central Brazil, with partially sympatric distributions. They have similar phenology and floral structure, although the flowers ofE. pubescens are larger. Both species have nectar flowers pollinated by largeAnthophoridae bees but the main pollinators of each species differ in size. The species have markedly different breeding systems: late-acting self-incompatibility inE. gracilipes and apomixis stimulated by pollination inE. pubescens.     

Observations of the floral biology ofPrasophyllum odoratum (Orchidaceae,Spiranthoideae)

Prasophyllum odoratum is a vernal, nectariferous, terrestrial orchid that flowers profusely six to eight months following cyclical fires that disrupt sclerophyll woodlands. The morphology of the column and pollinarium is indicative of taxa placed within the subfam.Spiranthoideae. The orientation of the pollinaria to the stigma appears to prevent mechanical self-pollination. Both cross- and self-pollination appear to be effected by insects that forage within the brightly-colored, scented, non-resupinate flowers. Ants and drosophilid flies remove nectar, but do not appear to transport pollinaria between flowers. The primary pollinators are polytrophic flies in the fam.Syrphidae and opportunistic male bees in the genusLeioproctus (Colletidae). Approximately 52% of the flowers on a raceme set seed. The comparatively short floral tube ofP. odoratum reflects the dependence of this species on short-tongued insects to effect successful dispersal of pollinaria.     

TheMoegistorhynchus longirostris (Diptera: Nemestrinidae) pollination guild: long-tubed flowers and a specialized long-proboscid fly pollination system in southern Africa

A guild of 20 late spring- and early summer-flowering species ofIridaceae, Geraniaceae andOrchidaceae is pollinated partly or exclusively by the long-proboscid flyMoegistorhynchus longirostris (Nemestrinidae). This large-bodied fly, active in late spring and early summer, has mouthparts 40–70 (90) mm long and forages for nectar from a variety of species. These plants share a suite of convergent floral features including a straight or weakly curved floral tube usually 50–70 mm long but sometimes to 90 mm, relatively short petals or tepal lobes coloured white, cream or salmon with reddish nectar guides, and often violet or red anthers and pollen. Flowers of most species with these characteristics are zygomorphic with the stamens either arcuate (mostIridaceae) or declinate (Geraniaceae and someIridaceae). The flowers are odourless and typically secrete large amounts of nectar of relatively constant sugar concentration, mostly 24–29%, with a high sucrose:hexose ratio. Guild members utilize five separate sites of pollen deposition on the body of the fly, typically utilizing different deposition sites when two or more co-occur, indicating strong selection to aviod pollen contamination.M. longirostris is restricted to the west coast of southern Africa and at least 8 species appear to depend exclusively on the insect for pollination. The remaining species in the guild are pollinated by one or both of the long-proboscid fliesPhiloliche gulosa andP. rostrata (Tabanidae) over other parts of their range. Species and races pollinated entirely byM. longirostris have longer floral tubes which makes nectar unavailable to other insects, including other species of long-proboscid fly. The only insect with mouthparts long enough to forage effectively on these long-tubed flowers isM. longirostris and this fly must be considered a keystone species in the ecosystems in which it occurs.Dedicated to emer. Univ.-Prof. DrFriedrich Ehrendorfer on the occasion of his 70th birthday     

Floral rewards in someScrophularia species (Scrophulariaceae) from the Iberian Peninsula and the Balearic Islands

The genusScrophularia in the Iberian Peninsula and Balearic Islands comprises two sections,Scrophularia andCanina G. Don. Analyses were carried out on flower production, flower duration and their sexual phases, pollen and nectar production together with observations on their pollinators. Nectar production is correlated with corolla size and pollen production with anther size. The taxa of sect.Scrophularia show greater nectar and pollen production than those of sect.Canina. Also, those of the first section produce more ovules per ovary than those of the second group, production being correlated with the ovary size.Some observations on floral and reproductive biology in some species ofScrophularia from the Iberian Peninsula and the Balearic Islands. I.     

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.     

Small but attractive: female‐biased nectar production and floral visitors in a dimorphic shrub

• In sexually dimorphic species, hermaphrodite flowers in gynodioecious species or male flowers in dioecious species are often larger and produce more nectar than their conspecific female flowers. As a consequence, hermaphrodite or male flowers frequently receive more pollinator visits.
• Sex ratio, flower size, floral display, nectar production and floral visits were evaluated in two natural populations of Fuchsia thymifolia, a morphologically gynodioecious but functionally subdioecious insect‐pollinated shrub.
• Sex ratio did not differ from the expected 1:1 in the two studied populations. As expected, hermaphrodite flowers were larger than female flowers, but in contrast to the general pattern, hermaphrodite flowers did not produce nectar or produced much less than female flowers. Flower visitors were flies (68%) and bumblebees (24%), both of which showed a preference for female flowers. No sex difference was detected in either flower longevity or floral display across the flowering season.
• Higher nectar production by females may attract more pollinators, and may be a strategy to enhance female reproductive success in this species. Finally, floral dimorphism and insect preferences did not seem to hamper the maintenance of sub‐dioecy or prevent the evolution of dioecy in F. thymifolia.

     

The effect of fire on flower visitation rate and fruit set in four core-species in east Mediterranean scrubland

The recovery of vegetation following fire has been studied intensively in Mediterranean-type ecosystems. Little attention, however, has been given to floral traits, and almost no data have been collected on the effects of fire on pollinator activity and fruit-set. This paper reports the effects of fire on flower visitation rates and the possibly related fruit-set. We compared visitation rates of the main pollinators on four plant core-species in burned and adjacent unburned areas. Measurements were performed at an unburned phrygana (scrub lands), and at a burned area (5–7 years post-fire). Bumble bees and solitary bees were the main taxa of visitors, while few honeybees were recorded. Solitary bees were almost absent from the burned area. Fruit-set was significantly higher in the unburned area for three out of the four plant species. The lower fruit-set in the burned area was possibly the result of low activity of solitary bees which are the main effective pollinators of the examined species. We hypothesize that the populations of the solitary bees were diminished or extirpated either directly by the fire, or indirectly by the scarcity of nectar in the early post-fire years due to dominance of young pine and Cistus spp. seedlings. The short foraging range of the solitary bees and their slow invasion rate into the burned area may explain our results.     

Interference and exploitation competition of three nectar-thieving invasive ant species

Summary. Plant and insect exudates are known to play a key role in structuring tropical ant communities, but less is known about the utilization of these resources in communities dominated by invasive ants. Invasive ants are thought to require large amounts of carbohydrates such as honeydew or nectar to maintain their high abundances. Invasive ants that consume floral nectar may compete with legitimate floral visitors through interference or exploitation competition. I compared the nectar-thieving behavior of three widespread invasive ant species: long-legged ants (Anoplolepis gracilipes), Argentine ants (Linepithema humile), and big-headed ants (Pheidole megacephala) in inflorescences of the native Hawaiian ‘ōhi’a tree, an important food source for native fauna. A. gracilipes was least likely to leave inflorescences unvisited and visited inflorescences in higher numbers than both L. humile and P. megacephala. A. gracilipes and L. humile visited more flowers in an inflorescence and were less likely to retreat from a flower with a competitor than P. megacephala. A. gracilipes was able to take 5.5 and 11.3 times the amount of nectar than L. humile and P. megacephala, respectively. Thus, A. gracilipes may be effective at both interference and exploitation competition against other nectarivores, L. humile may be effective at interference competition, and P. megacephala may be relatively weak at both types of competition against other nectarivores. Ascertaining the competitive abilities of invasive ants against legitimate floral visitors will be especially important in agricultural and other systems that are nectar or pollinator limited.Received 6 December 2004; revised 13 January 2005; accepted 14 January 2005.