Flower Lifetime Research Articles

Reproductive biology, variability of nectar features and pollination of Combretum fruticosum (Combretaceae) in Argentina

Flower morphology, nectary structure, nectar features (chemical composition, secretion pattern, standing crop, removal effects) and flower visitors are analysed in an Argentinian population of Combretum fruticosum. The variability of these data was examined throughout the flower lifetime. Nectar is hexose dominant. Its chemical composition and concentration are constant for all flowering stages. Nectar volume varies as a function of flower age due to a combination of nectar secretion, cessation and resorption periods. The overall sugar production is decreased by nectar removal. The plant is self-incompatible and xenogamous. Only 16.2% of the flowers set seeds. Inflorescences with green flowers were exclusively visited by two hummingbird and three perching bird species which transfer the pollen. A clear link was observed among nectar production pattern, standing crop of nectar, and visitors' behaviour.

Evolution of a Flower Dimorphism: How Effective is Pollen Dispersal by "Male" Flowers?

Many plants produce more flowers than will set fruit. In some species, a subset of flowers are actually female—sterile and morphologically distinct; these flowers are presumed to enhance fitness primarily through pollen donation. Individual plants of the hummingbird—pollinated shrub Besleria triflora produce both long—styled and short—styled flower morphs, characteristic of these "andromonoecious" sexual systems. Short—styled flowers set fruit rarely when hand—pollinated and are therefore functionally staminate. To test the hypothesis that selection for increased male function maintains flower dimorphism, I measured relative pollen dispersal per unit investment by staminate vs. perfect (long—styled) flowers. In the field, anthers of perfect flowers dispersed pollen for a significantly longer time than did those of staminate flowers. In laboratory experiments, hummingbirds transferred more pollen per visit from perfect flowers than from staminate flowers, in part due to differences in flower—morph pollen production. As a result, perfect flowers dispersed substantially more pollen than staminate flowers over an average flower lifetime. The two flower morphs did not differ in the amount of biomass invested through the time of corolla abscission, suggesting that staminate flowers do not conserve resources substantially. These results fail to support the "male—function" hypothesis for the evolution of andromonoecy. Staminate flowers contribute relatively little to plant reproductive success directly through male function, suggesting they are maintained for reproductive functions other than pollen donation.

Nectar Secretion Pattern and Removal Effects in Six Argentinean Pitcairnioideae (Bromeliaceae)

AbstractNectar secretion pattern and effects of nectar removal were analyzed in six hummingbird‐pollinated Argentinean Pitcairnioideae: Abromeitiella brevifolia. A. lorentziana, Deuterocohnia longipetala. Dyckia floribunda, D. ragonesei and Puya spathacea. Flower lifetime was determined in each case. Nectar volume, concentration and sugar production were measured from bud opening till fading of flowers at different time intervals according to the species' flower life‐span. Nectar volume varies while nectar concentration and cumulative sugar production increase as a function of flower age in all the studied species. In general, total nectar volume and concentration values can be affected by periodic removal, but total sugar production is unaffected. Only in Puya spathacea did periodic nectar harvesting reduce the total amount of sugar produced.

Pollination ecology and seed-set in the rare annual speciesMelampyrum arvenseL. (Scrophulariaceae)

SUMMARY Pollination of Melampyrum arvense L., a large-flowered hemiparasitic annual, was investigated in populations in The Netherlands, Germany, France and Switzerland. Pollination is achieved by bumblebees, with varying tongue lengths, collecting pollen and/or nectar. Long- and medium-tongued workers pollinate the flower nototribically (head-thorax pollination) and pollen-collecting short-tongued bumblebees sternotribically (venter pollination), as analysed by the actual transfer of fluorescent powder. Short-tongued bumblebees collect nectar by robbing the flowers, and sometimes also destroying the pistil. Nectar was present in a volume of 0.26 μl, with a sugar concentration of 30% and a ratio of fructose:glucose:sucrose = 1:0.67:0.73. M. arvense is self-fertile, but caged flowers do not produce seeds by the absence of auto-deposition. Artificial pollination showed that increasing pollination intensity increased fruiting, although after three pollinations fruiting did not increase and the number of seeds per fruit did. Observations in plots with variable plant density showed that during a low visitation intensity, flowers were visited at least 6.7 times during the flower's life span (7 days), and at a high visitation intensity 39.3 times. The additional effect on the seed-set of one-hand pollination during the flower's lifetime was low. Plants in low-density plots are highly branched in contrast to plants in high density. Branching of plants, resulting in more flowers per plant, and the fact that flowers on branches produce more seeds per flower, influence the total seed production per plant. The M. arvense population in The Netherlands had a rather high fruiting percentage and seed production per plant compared to three French populations.

The effects of nectar level and flower development on pollen carry-over in inflorescences of fireweed (Epilobium angustifolium) (Onagraceae)

Nectar in flowers of Epilobium angustifolium was manipulated experimentally to provide enriched versus depleted reward levels to bumblebee pollinators. Bumblebees visited significantly more flowers on inflorescences with high rewards than low ones and stayed longer on individual flowers with high rewards. The greatest pollen deposition occurred in older female flowers having enriched nectar levels. In older female flowers the stigma lobes coil backward, reducing the distance between their receptive surfaces and the nectary site. Younger female flowers, regardless of reward level, only occasionally received more than a few pollen grains per bee visit. Although higher nectar levels are likely to promote pollen receipt over the course of a flower's lifetime, because of changes in stigma configuration with flower development, the number of pollen grains transferred to the stigma at any given time depends on the flower's age as well as its reward status. In this self-compatible plant species, most of the increase in pollen receipt resulting from high nectar production is likely to lead to self-matings since (i) plants are clonal and bees usually fly to nearest neighbor ramets after rewarding visits, (ii) bees visit more flowers on enriched inflorescences than on depleted ones, and (iii) pollen carry-over declines exponentially over the course of an inflorescence visit.