Pistillate Phase Research Articles

Flower morphology and floral sequence in Artemisia annua (Asteraceae)1

• Artemisia annua produces phytochemicals possessing antimalarial, antitumor, anti-inflammatory, and anthelmintic activities. The main active ingredient, artemisinin, is extremely effective against malaria. Breeding to develop cultivars producing high levels of artemisinin can help meet worldwide demand for artemisinin and its derivatives. However, fundamental reproductive processes, such as the sequence of flowering and fertility, are not well understood and impair breeding and seed propagation programs.• Capitulum structure and floral sequence were studied using light and scanning electron microscopy to describe inflorescence architecture, floret opening, and seed set.• Florets are minute and born in capitula containing pistillate ray florets and hermaphroditic disk florets. Ray florets have elongated stigmatic arms that extend prior to disk floret opening. Disk florets exhibit protandry. During the staminate phase, pollen is released within a staminate tube and actively presented with projections at the tip of stigmas as the pistil elongates. During the pistillate phase, stigmatic arms bifurcate and reflex. Stigmas are of the dry type and stain positively for polysaccharides, lipids, and an intact cuticle. Floret numbers vary with genotype, and capitula are predominantly composed of disk florets. Both ray and disk florets produce filled seed.• Gynomonoecy, early opening of ray florets, and dichogamy of disk florets promote outcrossing in A. annua For breeding and seed development, flowering in genotypes can be synchronized under short days according to the floral developmental stages defined. Floret number and percentage seed fill vary with genotype and may be a beneficial selection criterion.

Floral functional structure, sexual phases, flower visitors and aspects of breeding system in Roella ciliata (Campanulaceae) in a fragmented habitat

Continued habitat destruction in lowland areas of the Western Cape, South Africa, due to urbanization has reduced Roella ciliata to a few isolated populations and it is unknown whether this endemic shrublet will persist. Here, we examine the reproductive biology of a small population of R. ciliata occurring in a residential nature reserve 30 km east of Cape Town to provide baseline information for future studies. Data were recorded on the functional structure of the flower, duration of the morphological gender phases, floral visitor profile and the relationship between breeding system and habitat. Observations revealed that this species possesses reproductive characteristics typical of Campanulaceae such as dichogamy, protandry and secondary pollen presentation via pollen collecting hairs. Floral longevity ranges between 1 and 3 days. Anthesis occurs in synchronicity at 0700 hours and individual flowers close between 0930 and 1500 hours daily. The staminate phase lasts between 2 and 29 h and is significantly influenced by the removal of pollen by floral visitors, while the pistillate phase lasts between 21 and 69 h. R. ciliata maintains a generalized, entomophilous pollination system although floral visitors are generally scarce. Despite some intraspecific variation, the pollen/ovule ratio indicates that R. ciliata has a facultatively autogamous breeding system, in contrast to its floral attributes which might favour xenogamy. This reproductive mechanism may ensure survival under these habitat conditions and could represent a shift from outcrossing to selfing at the cost of reducing genetic variation over time.

Absence of pollinators and apomictic fruit production in an Atlantic rainforest population of Cymbopetalum brasiliense (Annonaceae)

Breeding system and pollination biology of an isolated population of Cymbopetalum brasiliense (Annonaceae), a large-flowered understory tree, was studied during two consecutive flowering seasons in October/November 2007 and September/October 2008. Flowers were morphologically comparable to other Cymbopetalum species and generally to other Annonaceae taxa adapted to pollination by large beetles, such as Annona spp. Flowers were thermogenic and emitted a strong scent during the pistillate and staminate flowering phases. Heating of the floral chamber was most intense during the pistillate phase between 1800 and 1900 h (up to 6°C difference to air temperature). Floral scent consisted almost entirely of p-methylanisole. None of the 133 flowers examined during two seasons received any visitation by dynastid beetles or other potential pollinators. Lycaenid larvae (Oenomaus ortygnus) attacked buds and flowers in both flowering seasons and destroyed about 20% of all buds in the 2007 season. Fruit set was high (72% of nonpredated flowers in 2007), despite the absence of pollinators. Field experiments showed that agamospermic reproduction rather than self-pollination was most likely responsible for fruit production. The study reports a probable case of apomixis, which would be the first in the Annonaceae family.

Effects of Pollen in Lobelia laxiflora (Lobeliaceae) Long-Lived Flowers on Fecundity of Tropicoseius chiriquensis (Acari: Mesostigmata: Ascidae)

Abstract Pollen and nectar are the most important floral rewards in plant—pollinator interactions. These rewards are voraciously consumed by hummingbird flower mites (Acari: Mesostigmata: Ascidae), and nectar and pollen feeding by mites have a strong impact on plant—hummingbird interactions. Tropicoseius chiriquensis (Acari: Mesostigmata: Ascidae) feed on nectar and pollen of Lobelia laxiflora H.B.K. (Lobeliaceae) flowers, and within the floral corolla they mate and lay eggs. Yet the benefits of nectar and pollen feeding in terms of survival and fecundity of flower mites are quite unexplored. Here, we evaluate the fecundity and numerical response of T. chiriquensis to the availability of pollen in long-lived protandrous flowers of L. laxiflora. Under field conditions, unmanipulated flowers with pollen had more mites (adults, nymphs, larvae, and eggs) than emasculated flowers without pollen, Numbers of mites fluctuated throughout the flower life span. More adult mites were found for the first 2 d of the flower (staminate phase) and decreased for the last three days of life of the flower (pistillate phase). In contrast, we found higher number of larvae in the pistillate phase. In a laboratory experiment, the fecundity of flower mites was 4 times as high when pollen was available as that when flower mites were not provided with pollen. They completed their life cycle in approximately a week, the life span of L. laxiflora flowers. Our results suggest that pollen availability in L. laxiflora long-lived flowers could influence the population dynamics of T. chiriquensis by having a positive impact on numbers and fecundity of the mites.

Beetle visitations, and associations with quantitative variation of attractants in floral odors of Homalomena propinqua (Araceae)

This study investigated floral visitations of two beetles, Parastasia bimaculata (Scarabaeidae) and Chaloenus schawalleri (Chrysomelidae), and examined associations between beetle visitations and variation in attractant traits, such as quantitative variations of attractants in floral odors and heat generation of spadices in Homalomena propinqua (Araceae). Observations showed P. bimaculata visited pistillate-phase inflorescences most frequently during heat generation, whereas C. schawalleri visited regardless of floral stages and heat generation. Chemical analyses of five dominant components of floral odors showed quantities of 2-butanol, veratrole, and alpha-pinene during the pistillate phase were the most abundant during all floral stages, and increased during heat generation. When testing combinations of these five authentic chemicals, some mixtures including 2-butanol or veratrole or both attracted both beetles, and veratrole attracted C. schawalleri. These results strongly suggested that the increased emission of floral odor attractants which accompanied heat generation influences floral visitations by P. bimaculata, but not by C. schawalleri. We therefore hypothesize that P. bimaculataaculata is a reliable pollinator, and that variation in attractant traits is a honest signal for P. bimaculata to seek rewards. In contrast, C. schawalleri can detect the signal even at low levels, and so visits inflorescences steadily during all floral stages.

Fenologia de Syngonanthus mucugensis Giul. subsp. mucugensis e S. curralensis Moldenke (Eriocaulaceae), nos municípios de Mucugê e Morro do Chapéu, Chapada Diamantina, BA, Brasil

Syngonanthus mucugensis subsp. mucugensis e S. curralensis são conhecidas como sempre-vivas por possuírem capítulos que permanecem com a aparência de vivos durante anos. São plantas herbáceas com distribuição agrupada, folhas reunidas em roseta e inflorescências monóicas tipo capítulo, flores alvas e reduzidas. Este estudo apresenta os padrões fenológicos dessas espécies, relacionando-os com fatores abióticos e modo provável de dispersão. As observações foram realizadas mensalmente entre agosto/2002 e setembro/2004, em campo rupestre, nos municípios de Mucugê e Morro do Chapéu, registrando-se presença/ausência das fenofases. A fase vegetativa constitui grande parte do ciclo fenológico, aproximadamente cinco meses, na estação chuvosa (novembro-março). Os escapos levam três a quatro meses do início do desenvolvimento até a presença de capítulos jovens. As flores estaminadas e pistiladas apresentam ântese no início da manhã; as flores estaminadas duram um dia, e o ciclo estaminado cerca de sete dias. As flores pistiladas duram três dias e o ciclo pistilado três a quatro dias. Não ocorre sobreposição temporal das fases estaminada e pistilada em um mesmo capítulo. As duas espécies apresentaram padrão de floração (junho-agosto) e frutificação (julho-novembro) anual, regular, com duração intermediária, na estação seca. A dispersão ocorre ca. 45 dias após a fecundação, estendendo-se por quatro meses, durante a estação seca e início das chuvas. O tipo de diásporo e a dispersão sazonal sugerem dispersão anemocórica e autocórica.

Flowering and fruiting phenology of Normanbya normanbyi (W. Hill) L. H. Bailey (Arecaceae), a palm endemic to the lowland tropical rainforest of north‐eastern Australia

Abstract Normanbya normanbyi (W. Hill) L. H. Bailey (Arecaceae) is a monoecious, arborescent palm with a very small distribution area within the Daintree rainforest in north‐eastern Australia. Our 2‐year study was focused on the reproductive phenology at the individual and population level. At the population level flowering peaked in the dry season, whereas fruiting was confined to the wet season. Each palm can bear up to three inflorescences/infructescences at the same time. Flowering of each inflorescence is separated from each other by a couple of weeks. A single inflorescence consists of about 1900 staminate and 800 pistillate flowers. The flowering of N. normanbyi is protandrous with a staminate phase lasting 40 days and a pistillate phase of approximately 2 weeks. Between both phases is a non‐flowering phase of about 9 days. Fruit ripening takes 21 weeks, with an average of about 280 ripe fruit per tree. Comparison of three study plots revealed a moderate synchrony of flowering and fruiting initiation in this species of palm. The male phase of flowering shows a higher degree of synchrony than the female phase at the population level. Seasonal regularity of flowering and fruiting peaks appears to be predictable. The general flowering and fruiting phenology of N. normanbyi follows a subannual pattern with a strong tendency towards a continual pattern.

On flower visitors and true pollinators: The case of protandrous Heracleum sphondylium L. (Apiaceae)

Hogweed (Heracleum sphondylium L.), a common European umbellifer, is very variable in terms of flower and inflorescence morphology. Its flowers are visited by numerous insects, yet little is known about the importance of the particular insect taxa. I observed umbels of two colour morphs (subspecies) of Heracleum sphondylium growing in NE Poland, which were visited by more than 108 insect species during two study seasons. Analysis of the insects' importance suggests that the most efficient pollinators are the medium-sized flies Eriozona syrphoides, and Lucilia spp. (Diptera). Bumblebees Bombus terrestris (Hymenoptera), beetles of genus Stenurella spp. and Dasytes spp. (Coleoptera) and flies Eristalis spp., Meliscaeva cinctella, Phaonia angelicae and Thricops nigrifrons also contribute to pollination of the studied plants, but their efficiency shows considerable seasonal variation. Although the dense umbels of the white flowered H. sphondylium subsp. sphondylium are generally more attractive for insect visitors than the loose yellowish inflorescences of H. sphondylium subsp. sibiricum, these taxa do not seem to attract different sets of the pollinators. For both subspecies, flowers in the staminate phase were visited significantly more often than those in the pistillate phase. Some flower visitors visited the staminate phase only, which suggests they may be parasites rather than pollinators.

Floral nectar production and nectary anatomy and ultrastructure of Echinacea purpurea (Asteraceae).

In spite of the impressive species diversity in the Asteraceae and their widespread appeal to many generalist pollinators, floral-nectary ultrastructure in the family has rarely been investigated. To redress this, a study using Echinacea purpurea, a plant of horticultural and nutraceutical value, was undertaken. Nectar secretion of disc florets was compared with floral nectary ultrastructure taking into account nectar's potential impact upon the reproductive success of this outcrossing species. Micropipette collections of nectar in conjunction with refractometry were used to determine the volume and nectar-sugar quantities of disc florets throughout their phenology, from commencement of its production to cessation of secretion. Light, scanning-electron and transmission-electron microscopy were utilized to examine morphology, anatomy and ultrastructure of nectaries of the disc florets. Florets were protandrous with nectar being secreted from anthesis until the third day of the pistillate phase. Nectar production per floret peaked on the first day of stigma receptivity, making the two innermost whorls of open florets most attractive to foraging visitors. Modified stomata were situated along the apical rim of the collar-like nectary, which surrounds the style base and sits on top of the inferior ovary. The floral nectary was supplied by phloem only, and both sieve elements and companion cells were found adjacent to the epidermis; the latter participated in the origin of some of the precursor cells that yielded these specialized cells of phloem. Companion cells possessed wall ingrowths (transfer cells). Lobed nuclei were a key feature of secretory parenchyma cells. The abundance of mitochondria suggests an eccrine mechanism of secretion, although dictyosomal vesicles may contribute to a granulocrine process. Phloem sap evidently is the main contributor of nectar carbohydrates. From the sieve elements and companion cells, an apoplastic route via intercellular spaces and cell walls, leading to the pores of modified stomata, is available. A symplastic pathway, via plasmodesmata connecting sieve elements to companion, parenchyma and epidermal cells, is also feasible. Uncollected nectar was reabsorbed, and the direct innervation of the nectary by sieve tubes potentially serves a second important route for nectar-sugar reclamation. Microchannels in the outer cuticle may facilitate both secretion and reabsorption.

Variation in floral longevity between populations of Campanula rotundifolia (Campanulaceae) in response to fitness accrual rate manipulation

Floral longevity, the time between corolla expansion and senescence, contributes directly and indirectly to a plant's overall fitness. Though mating opportunities for insect-pollinated species often differ among populations, few empirical studies have addressed whether floral longevity varies in a manner consistent with these differences. I conducted experiments at thermally distinct sites to examine whether the prevailing floral longevity model predicted such variation between a montane and an alpine population of Campanula rotundifolia. Staminate phase duration was significantly shorter for montane vs. alpine C. rotundifolia flowers in the presence of pollinators, but significantly longer when pollinators were excluded. Montane flowers had a significantly higher female fitness accrual rate, significantly shorter total longevities, and, unlike alpine flowers, were not pollen-limited. Delaying pollinator access to pistillate phase flowers significantly increased total longevity in alpine flowers only. Significant differences in total longevity between populations resulted from an extended pistillate phase in alpine flowers. Overall, the prevailing model accurately predicted the total floral longevity trends found here. However, I provide novel evidence for geographic and gender-specific plasticity in the floral longevity response to fitness accrual rate variation, suggesting C. rotundifolia populations in this study may be attuned to local schedules of pollinator activity.

Pollination in Brazilian Syngonanthus (Eriocaulaceae) Species: Evidence for Entomophily Instead of Anemophily

The reproductive biology of Syngonanthus mucugensis and S. curralensis (Eriocaulaceae) was studied in areas of 'campo rupestre' vegetation in the Chapada Diamantina, north-eastern Brazil. These species are herbaceous and the individuals have a grouped distribution. Their leaves are united in a rosette, and their inflorescence is monoecious, of the capitulum type. The staminate and pistillate rings mature in a centripetal manner on the capitulum. A field study was conducted, including observations concerning the morphology and biology of the flowers, fruit development, insect visits and anemophily, in both S. mucugensis and S. curralensis. Experimental pollinations were also carried out to study the mating systems of S. mucugensis. Both species flower from June to August. The staminate cycle lasts approx. 7 d, and the pistillate cycle from 3 to 4 d, with no temporal overlap between them on the same capitulum. The pollen viability of S. mucugensis was 88.6%, and 92.5% for S. curralensis. The inflorescences of both species demonstrated ultraviolet absorbance, and a sweet odour was detected during both the staminate and pistillate phases. No nectar production was ever noted, although nectaries are present. Both species were visited by numerous groups of insects, with the Diptera being the principal pollinators, especially the species of Syrphidae and Bombyliidae. There were secondary pollinators among species of Coleoptera and Hymenoptera. There was no evidence of wind pollination. Syngonanthus mucugensis is a self-compatible species, and forms fruits by agamospermy at low frequencies. This is apparently the first report for pollination biology and mating systems of Eriocaulaceae. Conversely to that stated by some authors, entomophily, mainly effected by species of Diptera but also by species of Coleoptera and Hymenoptera, is probably the only pollination system in these species. In spite of the monoecious inflorescences without overlap of the staminate and pistillate phases, geitonogamy may occur in S. mucugensis, as the species is self-compatible and different capitula in the same plant at different phases is common.

Morphological and Functional Flower Characteristics of New and Old World Annonaceae with Respect to Their Mode of Pollination

The Annonaceae show a broader flower biological radiation than originally thought, with flowers being pollinated not only by beetles, but also by thrips, flies and even bees. The majority of species have hermaphroditic protogynous flowers. Species with white or yellowish-white, small, delicate, day-active flowers, may be pollinated either solely by thrips, or by thrips and small beetles (e.g., species of Bocageopsis, Oxandra, Xylopia). Several of these thrips-pollinated species have stamens with an elongated, tongue-like connective. Pollination by flies is not well documented for American species, notwithstanding it appears to be more common in Old World species, e.g., in the genus Pseuduvaria. The mitriform flowers exhale an unpleasant smell, produce nectar in purple-colored petal glands and have a sapromyiophilous syndrome. Flies enter the flower center through large openings between the inner petals. Beetle-pollinated Annonaceae have flowers with comparatively thick and, often, fleshy petals, which, during anthesis frequently form a pollination chamber with the petals inclining over the flower center. The stamens usually have peltate connective shields, probably a device for protection against voracious beetles. Some cantharophilous species have flowers which are day-active while others are night-active. When they are in their pistillate phase, the beetles are attracted by characteristic odor components. They enter the pollination chamber and usually remain in the interior of the flower until the flower has changed to its staminate phase, when pollen is shed and afterwards petals and stamens detach. Two lines of cantharophilous Annonaceae are recognizable on the basis of present knowledge. Species with smaller and more delicate flowers are pollinated by small beetles (Nitidulidae, Curculionidae, Chrysomelidae and Staphylinidae), whereas species with large, more robust flowers in the Neotropics are pollinated by large beetles of the family Scarabaeidae, subfamily Dynastinae. Some species of the cantharophilous Annonaceae, especially the large-flowered ones, but also some species with smaller flowers, produce heat during anthesis (thermogenesis). Food bodies, developed on the adaxial surfaces or sides of the petals, provide unique nourishment possibilities for beetles when they stay inside the flowers during the pistillate phase. In the staminate stage of the flower, after pollen is shed, beetles also feed on pollen. Apparently, no dynastid-flower relationship has evolved in Asia and Australia. Pollination by bees was discovered recently in Unonopsis guatterioides in Amazonia and Uvaria concava in North Queensland: the first by scent-collecting euglossine males and the second by pollen-collecting Meliponinae. The general trends in morphological/functional floral characteristics in the family are discussed in a presumptive phylogenetic context.

Morphological and functional flower characteristics of New and Old World Annonaceae with respect to their mode of pollination

The Annonaceae show a broader flower biological radiation than originally thought, with flowers being pollinated not only by beetles, but also by thrips, flies and even bees. The majority of species have hermaphroditic protogynous flowers. Species with white or yellowish‐white, small, delicate, day‐active flowers, may be pollinated either solely by thrips, or by thrips and small beetles (e.g., species of Bocageopsis, Oxandra, Xylopia). Several of these thrips‐pollinated species have stamens with an elongated, tongue‐like connective. Pollination by flies is not well documented for American species, notwithstanding it appears to be more common in Old World species, e.g., in the genus Pseuduvaria. The mitriform flowers exhale an unpleasant smell, produce nectar in purple‐colored petal glands and have a sapromyiophilous syndrome. Flies enter the flower center through large openings between the inner petals. Beetle‐pollinated Annonaceae have flowers with comparatively thick and, often, fleshy petals, which, during anthesis frequently form a pollination chamber with the petals inclining over the flower center. The stamens usually have peltate connective shields, probably a device for protection against voracious beetles. Some cantharophilous species have flowers which are day‐active while others are night‐active. When they are in their pistillate phase, the beetles are attracted by characteristic odor components. They enter the pollination chamber and usually remain in the interior of the flower until the flower has changed to its staminate phase, when pollen is shed and afterwards petals and stamens detach. Two lines of cantharophilous Annonaceae are recognizable on the basis of present knowledge. Species with smaller and more delicate flowers are pollinated by small beetles (Nitidulidae, Curculionidae, Chrysomelidae and Staphylinidae), whereas species with large, more robust flowers in the Neotropics are pollinated by large beetles of the family Scarabaeidae, subfamily Dynastinae. Some species of the cantharophilous Annonaceae, especially the large‐flowered ones, but also some species with smaller flowers, produce heat during anthesis (thermogenesis). Food bodies, developed on the adaxial surfaces or sides of the petals, provide unique nourishment possibilities for beetles when they stay inside the flowers during the pistillate phase. In the staminate stage of the flower, after pollen is shed, beetles also feed on pollen. Apparently, no dynastid‐flower relationship has evolved in Asia and Australia. Pollination by bees was discovered recently in Unonopsis guatterioides in Amazonia and Uvaria concava in North Queensland: the first by scent‐collecting euglossine males and the second by pollen‐collecting Meliponinae. The general trends in morphological/functional floral characteristics in the family are discussed in a presumptive phylogenetic context.

Pollination of Anthurium (Araceae) by derelomine flower weevils (Coleoptera: Curculionidae)

Cyclanthura flower weevils (Coleoptera: Curculionidae: Derelomini) are identified for the first time as pollinators of multiple species of Anthurium (Araceae) in Costa Rica. The weevils are present on the inflorescences in small numbers during the pistillate and staminate phase of anthesis, and consume plant tissues and pollen. The individuals of one species of Cyclanthura can visit several Anthurium species within the same locality. They also engage in reproductive activities and are likely to oviposit into the flowers. The mating strategies suggest that sperm precedence selects males that are able to secure their position as the last partner prior to oviposition.

Floral scents affect reproductive success in fly‐pollinated Alocasia odora (Araceae)

We evaluated the role of floral scents in the reproductive success of Alocasia odora C. Koch (Araceae). Alocasia odora is pollinated by its specific pollinators, Colocasiomyia alocasiae (Okada) and C. xenalocasiae (Okada) (Diptera: Drosophilidae). These flies use the spadix of A. odora as breeding sites. The appendix, which is at an upper part of the spadix and is the most attractive region, attracted these pollinators by emitting volatiles, although the male zone of the inflorescence was also attractive. The number of flies attracted was positively correlated with appendix size. During the pistillate phase of the protogynous spadix, attracted flies aggregated in the lower part (female zone) to mate, lay eggs, and perhaps obtain nutrients. The flies moved to the upper part (male zone) of the spadix by the tightening of the constriction separating the upper and lower parts, and then the staminate phase started. This movement of the flies on the spadix promotes outcrossing of A. odora. Removal of the appendix or the whole upper part of the spadix resulted in much reduced fruit set, suggesting that the absence of the scent-producing region leads to insufficient pollination because of reduced pollinator attraction.

Mating behaviour of Staminodeus vectoris (Coleoptera: Curculionidae), and the value of systematics in behavioural studies

The mating behaviour of Staminodeus vectoris Franz (Curculionidae: Curculioninae: Derelomini) is described and discussed in light of a phylogeny of Staminodeus Franz. At La Selva, Costa Rica, S. vectoris is associated with the staminodes of the inflorescences of Asplundia uncinata Harling and several other species of Cyclanthaceae. The males have a row of 6–10 teeth along the margin of the protibia, whereas the females have a small, curved spine on the frons. The adults arrive in numbers at the inflorescences during the pistillate phase of the anthesis of A. uncinata, feeding on the staminodes. Eventually, a female detaches a staminode with her mandibles, falls to the ground, and transports it to the site of oviposition in the leaf litter. First, she crawls underneath the staminode, then moves it posteriorly with her legs, and finally returns to its distal end before repeating the process. The female turns on her back and maintains her original position during the movement of the staminode, using her frontal spine as a point of resistance against the substrate. Meanwhile, a male associates with the staminode. The males fight with their prothoracic legs, executing fast blows until their protibial teeth cling and dislodge competitors from the staminode. The positive and negative allometries of the lengths of the male protibia and female spine, are consistent with their functions in the contexts of sexual and natural selection, respectively. The phylogeny of all seven species of Staminodeus hypothesises that female transporting behaviour evolved before male fighting behaviour.

Pollination Biology and Flower Visitors of the Gynodioecious Species Lobelia spicata Lam. (Campanulaceae)

Molano-Flores, B. (Illinois Natural History Survey-Center for Biodiversity, 607 E. Peabody Drive, Champaign, Illinois 61820). Pollination biology and flower visitors of the gynodioecious species Lobelia spicata Lam. (Campanulaceae). J. Torrey Bot. Soc. 129: 187-193. 2002.-The pollination biology and flower visitors of Lobelia spicata, an herbaceous prairie perennial, were examined, and this species was found to be xenogamous, self-compatible, and gynodioecious. Hermaphroditic individuals are protandrous, produce nectar, and have secondary pollen presentation (i.e., pump mechanism). Female individuals do not produce nectar. No significant differences were found between the fruit set of open-pollinated hermaphroditic and female flowers. In hermaphroditic bagged flowers seeds were produced (i.e., undeveloped fruits) suggesting self-pollination; however, this was determined to be the result of geitonogamous pollination by thrips. Autogamy is not likely in this species because there is no overlap between the staminate and pistillate phases. This species is pollinated mainly by bees from the genus Augochlorella. Overall, this study shows that L. spicata shares many common characteristics with other species of Lobelia (i.e., L. cardinalis and L. siphilitica) such as protandry, self-compatibility, no autonomous self-pollination, similar flower phenology (i.e., pistillate and staminate phases), and secondary pollen presentation (i.e., pump mechanism). In contrast to these other species, L. spicata blooms early, has smaller flowers, and attracts smaller pollinators.

The role of autonomous self‐pollination in floral longevity in varieties of Impatiens hypophylla (Balsaminaceae)

The floral longevity of unpollinated, hand self-, and hand cross-pollinated flowers was compared in two varieties of Impatiens hypophylla, which contrasts with their mating systems. When flowers were emasculated and hand-pollinated every day after anthesis, their longevity was reduced. In the absence of emasculation and hand pollination, the staminate phase of the flowers of both varieties was 1 d longer. After the staminate phase, flowers of the outcrossing variety dropped their androecium, exposing the stigma and initiating the pistillate phase, which lasted for ∼2 d. In contrast, flowers of the mixed-mating variety self-pollinated autonomously and then terminated their flowering. Under great seasonal variation in the pollinator visitation rate, which was observed in their natural populations, the outcrossing variety should maximize expected outcross success through the phenology of floral sex phases, whereas the mixed-mating variety self-pollinated ovules that were not outcrossed within the staminate phase. Based on these results, I suggest that the autonomous self-pollination in I. hypophylla induced differences both in the selfing coefficient and in floral longevity between the varieties.

Nectar ‘theft’ by hummingbird flower mites and its consequences for seed set in Moussonia deppeana

Summary Mites (Acari: Mesostigmata: Ascidae) that live and feed in the flowers of about 100 plant species are transported in the nares of hummingbirds (Trochilidae). Mites may compete with hummingbirds for nectar secreted by the host plants, and this could affect the dynamics and reproductive outcomes of the mutualism between plants and their pollinating hummingbirds. Here we combined field observations and experimental manipulations to assess the role of hummingbird flower mites (Tropicoseius sp. nov.) on nectar secretion and reproductive output of protandrous Moussonia deppeana (Schlecht. & Cham.) Hanst. (Gesneriaceae) during their flowering period in a cloud forest remnant. During the 4 days that the flowers of M. deppeana last, flowers were visited exclusively by hummingbirds (Lampornis amethystinus). Bud production per inflorescence peaked in December. There were few open flowers per inflorescence in November, but numbers increased as the flowering season progressed (December and January). The availability of each flower phase differed over the flowering season. Staminate‐phase flowers were more abundant over the flowering season than pistillate‐phase flowers. These differences were statistically significant over time. Nectar availability was reduced by up to 50% in the presence of hummingbird flower mites. Over the 4 days of observation, significantly more nectar was secreted to flowers from which mites were excluded than to flowers with no mite exclusion. The same effect was observed during flowering, but mites consumed a greater percentage of the total nectar secreted in December. Significantly more nectar was secreted during the staminate phase than in the pistillate phase, independent of time and treatment. A manual pollination experiment suggested that mites act like secondary pollinators in this self‐compatible, non‐autogamous plant, at least in flowers that were not pollinated manually and had no access to pollinating hummingbirds. Although seed production was not reduced significantly by flower mites, our results suggest that the presence of floral mites can affect pollen transmission, as the amount of nectar available to hummingbirds was reduced drastically. This can directly affect hummingbird foraging patterns and reduce the fitness of the host plants.

FLOWER SEX RATIO, POLLINATOR ABUNDANCE, AND THE SEASONAL POLLINATION DYNAMICS OF A PROTANDROUS PLANT

The separation between staminate and pistillate phases in protandrous, long-lived hermaphroditic flowers results in a seasonal shift in sex ratio from a pure male to a pure female flower population. In theory, temporal sex ratio associated with dichogamy may affect pollination, promoting the evolution of sexual specialization in plants when pollinator visitation does not limit seed output. Alstroemeria aurea, a perennial herb native to the temperate forests of southern South America, bears strongly protandrous flowers. Over a three-year period, I assessed the influence of seasonal changes in flower sex ratio and pollinator abundance on the pollination dynamics of this plant species. Workers of Bombus dahlbomii accounted for >90% of all visits to A. aurea flowers and were the most efficient pollinators on a per-visit basis. As the season progressed, pollen loads carried by bumble bees decreased by almost one order of magnitude, and the amount of pollen deposited per visit decreased as well from >40 to <4 pollen grains from the beginning to the end of the flowering season. As flowering patches became more female, the number of male-phase flowers visited uninterruptedly during each bumble bee foraging bout decreased, while the number of sequential visits to female-phase flowers increased. A laboratory experiment of manipulating dried bumble bees showed that the number of male- and female-phase flowers visited in uninterrupted sequence strongly influences the amount of pollen deposited on a flower's stigma. Pollen deposition in this experiment closely mimicked the relationship between sex ratio and the observed seasonal decline in per-visit pollen deposition in the field. Because overall rate of bumble bee visitation increased monotonically over the flowering season, total pollen receipt per flower also increased during the first half of the season. Nevertheless, pollen deposition decreased during the second half of the season when visitation rates saturated pollen removal, and low pollen availability associated with an increasingly female-biased sex ratio apparently became the limiting factor in pollen transfer. Despite pronounced seasonal changes in pollinator and pollination levels, comparisons of seed output between open- and hand-pollinated flowers showed no evidence that seed production was ever limited by total pollen receipt. Because flower sex ratio influenced pollinator visitation and pollination patterns, and pollinator availability did not limit seed output, protandry should favor the evolution of female and male specialists flowering at the tails of the flowering season. Neither unisexuality nor any other form of sexual polymorphism is found in A. aurea, however. Likewise, I found no evidence that plants might be compensating for a seasonal shift in sex ratio through differential allocation into pollen and ovule production within flowers or to relative duration of male and female sexual phases. These results suggest that a seasonal shift in operational sex ratio within a dichogamous species can profoundly affect pollination without necessarily driving the evolution of floral polymorphism.