Floral Units Research Articles

Automating field‐based floral surveys with machine learning

Abstract The abundance and diversity of flowering plant species are important indicators of pollinator habitat quality, but traditional field‐based surveying techniques are time‐intensive. Therefore, they are often biased due to under‐sampling and are difficult to scale. Aerial photography was collected across 10 sites located in and around Rouge National Urban Park, Toronto, Canada using a consumer‐grade drone. A convolutional neural network (CNN) was trained to semantically segment, or identify and categorize, pixel clusters which represent flowers in the collected aerial imagery. Specifically, flowers of the dominant taxa found in the depauperate fall flowering plant community were surveyed. This included yellow flowering Solidago spp., white Symphyotrichum ericoides/lanceolatum and purple Symphyotrichum novae‐angliae. The CNN was trained using 930 m2 of manually annotated data, ~1% of the mapped landscape. The trained CNN was tested on 20% of the manually annotated data concealed during training. In addition, it was externally validated by comparing the predicted drone‐derived floral abundance metrics (i.e. floral area (m2) and the number of floral patches) to the field‐based count of floral units estimated for 34 4 m2 plots. The CNN returned accurate multiclassification when evaluated against the testing data. It obtained a precision score of 0.769, a recall of 0.849, and an F1 score of 0.807. The automated floral abundance counting yielded estimates that were strongly correlated with field‐based manual counting. In addition, flower segmentation using the trained CNN was time‐efficient. On average, it took roughly the same amount of time to segment the flowers occurring in an entire drone scene as it took to complete the abundance count of a single quadrat. However, the training process, particularly manual data annotation, was the most time‐consuming component of the study. Practical implication: Overall, the analysis provided valuable insights into automated flower classification and abundance estimation using drone imagery and machine learning. The results demonstrate that these tools can be used to provide accurate and scalable estimates of pollinator habitat quality. Further research should consider diverse wildflower systems to develop the generalizability of the methods.

Drought response and urban-pollinator attractiveness of ornamental plant species

Faced with pollinator declines, cities could serve as refuges for biodiversity conservation by managing floral resources in public green spaces. Ornamental plants could play an important role in attracting pollinators because they form part of urban floral management. However, knowledge of how their floral traits respond to drought is lacking, and it is unknown whether they will be suitable for pollinators under future climates. The main objective of this study was to determine the covariation of floral traits of ornamental plant species and effects of drought on them. To this end, in a city greenhouse we measured floral traits of eight ornamental species commonly used in urban green spaces in France. We subjected the plants to a control treatment or a drought treatment, reducing the volume and frequency of watering. We observed interspecific variability in floral traits among these species and a change in covariation between the traits pollen quantity and nectar quantity in the drought treatment. Drought influenced morphological traits related to floral display more than other floral traits, with mean decreases of 28 % in floral height, 35 % in floral area and 58 % in the number of floral units. Ornamental plants seemed attractive to different morphotypes of pollinators depending on their floral unit number, nectar sugar concentration or nectar tube depth, with most visits made by Hymenoptera. These results are expected to encourage green-space managers to select urban plants according to their functional characteristics and adapt their choice of plants to climate change.

Quantifying the production of plant pollen at the farm scale.

Plant pollen is rich in protein, sterols and lipids, providing crucial nutrition for many pollinators. However, we know very little about the quantity, quality and timing of pollen availability in real landscapes, limiting our ability to improve food supply for pollinators. We quantify the floral longevity and pollen production of a whole plant community for the first time, enabling us to calculate daily pollen availability. We combine these data with floral abundance and nectar measures from UK farmland to quantify pollen and nectar production at the landscape scale throughout the year. Pollen and nectar production were significantly correlated at the floral unit, and landscape level. The species providing the highest quantity of pollen on farmland were Salix spp. (38%), Filipendula ulmaria (14%), Rubus fruticosus (10%) and Taraxacum officinale (9%). Hedgerows were the most pollen-rich habitats, but permanent pasture provided the majority of pollen at the landscape scale, because of its large area. Pollen and nectar were closely associated in their phenology, with both peaking in late April, before declining steeply in June and remaining low throughout the year. Our data provide a starting point for including pollen in floral resource assessments and ensuring the nutritional requirements of pollinators are met in farmland landscapes.

What are the drivers of female success in food-deceptive orchids?

A large suite of floral signals, and environmental and biotic characteristics influence the behavior of pollinators, affecting the female success of food-deceptive orchids. In this study, we examined the many factors shaping the reproductive output of three orchid taxa: Dactylorhiza majalis, D. incarnata var. incarnata, and D. fuchsii. We applied a statistical model to correlate female success (number of fruit sets) with individual characteristics (plant and inflorescence height, number of flowers, and spur length), number of pollinaria removed, flowering time, and density of floral units of co-flowering rewarding plants. Our findings suggested that the broad spectrum of variations in Dactylorhiza's morphological traits, floral display, and flowering phenology within different environmental contexts has a significant impact on their reproductive success. The number of fruits increased with an increase in the number of pollinaria removed in the studied Dactylorhiza taxa. In contrast, a higher number of flowers per inflorescence and higher inflorescences in relation to individual height always decreased fruit set. We observed that low number of co-flowering rewarding plants in populations could affect the Dactylorhiza reproductive output as magnets and competitor plants. The synchronization of flowering, or lack thereof, between Dactylorhiza and rewarding plants can limit reproductive success. This demonstrates that the food deception strategy is multidirectional, and reproductive output can vary considerably both spatially and temporally within the context of this strategy.

Multifunctional bioretention basins as urban stepping stone habitats for wildflowers and pollinators

Sustainable Urban Drainage Systems (SUDS) are increasingly used to manage precipitation events in cities and create decentralized stormwater management. To enhance ecological benefits of bioretention basins, we investigated development of native forb communities composed of 26 plant species common in northwest Europe, their provision of foraging resources, and functional connectivity between basins for pollinating insects. We used two types of engineered infiltration soil to test effects of growing conditions on plants in four basins under field conditions over three years, and in a controlled environment. Hemi-rosette grassland forbs associated with neutral to calcareous sandy soils tolerated the environmental conditions and persisted during early succession, while there was no effect of infiltration soil on community composition. Furthermore, colonisation by non-sown spontaneous plants was limited, but differed between soil types. Sown forbs and spontaneous wildflowers contributed foraging resources to local pollinators. Fluorescent dye was moved between forbs in all basins, while bi-directional dye dispersal up to 86 m demonstrated basins facilitate functional connectivity for pollinating insects whereby structurally disconnected basins contribute as stepping-stone habitat patches. Finally, in the controlled experiment testing the effect of soil types on plant growth (aboveground biomass) and reproduction (floral units) of eight native forbs, results indicated that infiltration soils should maximise organic content to enhance species richness in bioretention basins, albeit without compromising system performance. Despite low replication in the field study, we demonstrate bioretention basins can support urban biodiversity conservation by providing valuable foraging habitat and functional connectivity for pollinators while requiring minimal management.

Features of Seed Reproduction of <i>Saposhnikovia divaricata</i> (Apiaceae)

Abstract—Saposhnikovia divaricata (Turcz. ex Ledeb.) Schischk. (Apiaceae) is a useful medicinal plant, which contain a number of substances with a wide range of pharmacological activity; chromones, in particular, are found in the roots. For this reason, plants are heavily harvested from the wild, resulting in the population low density. S. divaricata is a taproot perennial monocarpic that reproduces by seeds only. The introduction of the species, the study of seed productivity and seed reproduction is a vital task for the development of industrial plant cultivation and the restoration of natural populations. The purpose of this work is to study seed production and biology of seed propagation. The generative shoot of S. divaricata is a synflorescence (a panicle of double umbels) with a floral unit being a double umbel. Plants from natural habitat and cultivated ones were studied. A comparative analysis of the seed production of double umbels, depending on their position on the rachis was carried out. The proportion of seed set (seed number/ovule number) and fruit set (fruit number/flower number) in a simple umbel, the potential and real seed productivity of a simple umbel, double umbel, and an individual plant were determined. Fruit of S. divaricata is a cremocarp consisting of two single-seeded mericarps. The seeds have a thin spermoderm, so they were stored and germinated with the pericarp. Seeds (mericarps) for germination were collected from natural populations and cultivated plants considering their position on the rachis, and stored for eight months under laboratory conditions (+23–25 °C). The results of the experiment included data on the duration of the period from the beginning of the experiment to the seed germination, the duration of the germination period (from the beginning of germination), laboratory germination of seeds (%), germination energy (%), rate of germination energy (%). All cultivated plants were monocarpic. The diameter of the synflorescence reaches 124 cm; on average, about 70 double umbels with fruits are formed on it. It was found that in introduced plants, seeds from the branches of the third order make up more than 50% of the real seed production, and from the second and fourth order branches – 21 and 26%, respectively. In natural populations, seeds from the fourth order branches account for 45% of the real seed production, of the third – 30%, of the 2nd – 15%. In the introduced plants, the real seed production of the second generation was about 6000 seeds per individual, which is higher than that of plants in natural populations, where the seed set is 65%. The seeds exhibit non-deep dormancy, and the period before germination does not exceed 10 days. Seed germination is dynamic; more than 50% of the germinated seeds have sprouted within seven days. Laboratory germination was higher in the seeds from the natural population, than from the introduced plants. The highest laboratory germination in introduced plants was found in seeds from double umbels of the second or third order branches – 72–73%, and from the natural populations – in seeds from the shoots of the third or fourth order branches – more than 90%.

Flower surface is warmer in center than at edges in alpine plants: evidence from Qinghai-Tibetan Plateau

Abstract Although flower temperature plays an important role in plant reproduction, how it varies spatially on the flower surface is unclear, especially in alpine plants. To characterize spatial variation in flower surface temperature, we examined thermal images of flowers of 18 species along an altitudinal transect from 3200 to 4000 m on Lenglong Mountain on the north-eastern Qinghai-Tibetan Plateau. The surface temperature varied considerably within a flower or floral unit in all plants under sunlight, and was about 1 °C with a maximum of 11 °C higher in the center than at the edges. Solar radiation and flower shape significantly affected the temperature range and standard deviation and the ratio of flower center to edge temperature. The spatial variability of temperature increased with flower size. Flowers in the Asteraceae had higher surface temperatures, greater spatial variability of temperature, and consistently higher and more stable temperatures in the center than at the edge. The ratio of flower center to edge temperature increased with altitude in most species. Heat buildup at the flower center is likely to be widespread in alpine plants; further studies are needed to explore its ecological and evolutional roles.

Floral resources in Swedish grasslands remain relatively stable under an experimental drought and are enhanced by soil amendments if regularly mown

Abstract One of the main reasons why insect pollinators are declining is a lack of floral resources. In agricultural landscapes, remaining seminatural grasslands play a key role for providing such resources. However, droughts pose an increasing threat to the abundance and continuity of flowers. Soil amendments are a novel management tool for Swedish grasslands aiming to increase carbon sequestration and soil water holding capacity. In this study, we examined how drought is affecting floral resources (i.e. floral units, nectar quantity and nectar continuity) in grasslands with different mowing regimes, and if soil amendments could mitigate potential negative drought effects. In summer 2019, we set up an experiment combining rain‐out shelters (‘drought’), soil amendments (‘compost’) and different mowing regimes (‘mown’ vs. ‘abandoned’) in four extensively managed Swedish grasslands (48 plots, size 2 m2). Between May and August 2021, we counted the floral units nine times in each plot. We derived values for the nectar sugar production per floral unit from an existing database. We observed a decrease in floral units under drought in the mown, but not in the abandoned plots. Nectar quantity and continuity over the season were not significantly affected by drought across both mowing regimes—in the abandoned plots the nectar provision even extended slightly in duration (towards late summer). The compost treatment had positive effects on the floral units, nectar quantity and continuity (extending it towards early summer) in the mown, but not in the abandoned plots. The plant species in our study reacted differently to the treatments. Most of the nectar was provided by only few species (mainly Lathyrus pratensis, Vicia cracca and Anthriscus sylvestris). The results are species specific, thus other plant communities might respond differently. However, our experiment shows that nectar provision (based on database values) in grasslands with a native plant community and natural soil conditions remains relatively stable under drought. We also found that soil amendments increase floral resources in managed grasslands.

A dataset of nectar sugar production for flowering plants found in urban green spaces

Abstract Nectar and pollen are floral resources that provide food for insect pollinators, so quantifying their supplies can help us to understand and mitigate pollinator declines. However, most existing datasets of floral resource measurements focus on native plants found in rural landscapes, so cannot be used effectively for estimating supplies in urban green spaces, where non‐native ornamental plants often predominate. We sampled floral nectar sugar in 225 plant taxa found in UK residential gardens and other urban green spaces, focussing on the most common species. The vast majority (94%) of our sampled taxa are non‐native, filling an important research gap and ensuring these data are also relevant outside of the United Kingdom. Our dataset includes values of daily nectar sugar production for all 225 taxa and nectar sugar concentration for around half (102) of those sampled. Nectar extraction was conducted according to published methods, ensuring our values can be combined with other datasets. We anticipate that the two main uses of these data are (1) to estimate the nectar production of habitats and landscapes and (2) to identify high‐nectar plants of conservation importance. To increase the utility of our data, we provide guidance for scaling nectar values up from single flowers to floral units, as is commonly done in field studies.

The Structural–Rhythmological Organization of Coelogyne (Orchidaceae Juss.) Inflorescences

The morphostructure of inflorescences in the genus Coelogyne Lindl. was studied for the first time using a structural–rhythmological approach. Three species of Coelogyne were used to describe one-season, intercalary, and all-season inflorescences. In C. monilirachis, a new type of all-season inflorescence was identified, characterized by a prolonged sympodial growth of the rachis, lack of a pronounced dormant period, and thickening of all rachis internodes except the first. This inflorescence has been determined to be a compound monochasial cyme, with each floral unit represented by a separate flower. C. ovalis has a one-season inflorescence, with the floral unit being a determinate bracteous spike (stachyoid), and C. prolifera developed intercalary inflorescences united in an indeterminate bracteous spike.

Flower-like meristem conditions and spatial constraints shape architecture of floral pseudanthia in Apioideae

BackgroundPseudanthia are multiflowered units that resemble single flowers, frequently by association with pseudocorollas formed by enlarged peripheral florets (ray flowers). Such resemblance is not only superficial, because numerous pseudanthia originate from peculiar reproductive meristems with flower-like characteristics, i.e. floral unit meristems (FUMs). Complex FUM-derived pseudanthia with ray flowers are especially common in Apiaceae, but our knowledge about their patterning is limited. In this paper, we aimed to investigate both the genetic and morphological basis of their development.ResultsWe analysed umbel morphogenesis with SEM in six species representing four clades of Apiaceae subfamily Apioideae with independently acquired floral pseudanthia. Additionally, using in situ hybridization, we investigated expression patterns of LEAFY (LFY), UNUSUAL FLORAL ORGANS (UFO), and CYCLOIDEA (CYC) during umbel development in carrot (Daucus carota subsp. carota). Here, we show that initial differences in size and shape of umbel meristems influence the position of ray flower formation, whereas an interplay between peripheral promotion and spatial constraints in umbellet meristems take part in the establishment of specific patterns of zygomorphy in ray flowers of Apiaceae. This space-dependent patterning results from flower-like morphogenetic traits of the umbel which are also visible at the molecular level. Transcripts of DcLFY are uniformly distributed in the incipient umbel, umbellet and flower meristems, while DcCYC shows divergent expression in central and peripheral florets.ConclusionsOur results indicate that umbels develop from determinate reproductive meristems with flower-like characteristics, which supports their recognition as floral units. The great architectural diversity and complexity of pseudanthia in Apiaceae can be explained by the unique conditions of FUMs—an interplay between expression of regulatory genes, specific spatio-temporal ontogenetic constraints and morphogenetic gradients arising during expansion and repetitive fractionation. Alongside Asteraceae, umbellifers constitute an interesting model for investigation of patterning in complex pseudanthia.

The FloRes Database: A floral resources trait database for pollinator habitat-assessment generated by a multistep workflow.

The decline of pollinating insects in agricultural landscapes proceeds due to intensive land use and the associated loss of habitat and food sources. The feeding of those insects depends on the spatial and temporal distribution of nectar and pollen as food resource. Hence, to protect insect biodiversity, a spatio-temporal assessment of food quantity of their habitats is necessary. Therefore, sufficient data on traits of floral resources are required. As floral resources' traits of plants are important to quantify food availability, we present two databases, the FloRes Database (Floral Resources Database) and the raw database, from where FloRes was derived. Both databases contain the plant traits: (1) flowering period, (2) floral-unit density per day, (3) nectar volume per floral unit per day, (4) sugar content per floral unit, (5) sugar concentration in nectar, (6) pollen mass or volume per floral unit and per day, (7) protein content of pollen and (8) corolla depth. All traits were sampled from literature and online databases. The raw database consists of 702 specified plant species, 138 unspecified species 37 species (spec., sp), 22 species pluralis (spp) and, for 79, only the genus was identified) and two species complexes (agg.). Those 842 taxa belong to 488 genera and 102 families. Finally, only 27 taxa have a complete set of traits, too few for a sufficient assessment of spatio-temporal availability of floral food-resources.As information on floral resources is scattered throughout many publications with different units, we also present our multistep workflow implemented in five consecutive R-scripts. The multistep workflow standardises the trait units of the raw database to comparable entities with identical units and aggregates them on a reasonable taxonomic level into the second application database, the FloRes Database. Finally, the FloRes Database contains aggregated information of traits for 42 taxa and, when corolla depth is excluded, for 72 taxa.This is the first attempt to gather these eight traits from different literature sources into one database with a multistep workflow. The publication of the multistep workflow enables the users to extend the FloRes Database on their own demands with other literature data or newly-gathered data to improve quantification of food resources. Especially, the combination of pollen, nectar and the open flowers per square metre is, as far as we know, a novelty.The FloRes Database can be used to evaluate the quantity of food-resource habitats available for pollinators, for example, to compare seed mixtures of agri-environmental measures, such as flower strips, considering flower phenology on a daily basis.

Evaluating the effects of observation period, floral density, and weather conditions on the consistency and accuracy of timed pollinator counts

Insect pollinators are experiencing substantial declines as a result of habitat loss, agricultural intensification, invasive pests, and climate change. To investigate factors causing pollinator declines, evaluate the success of conservation measures, and institute long-term monitoring schemes, it is essential to validate and standardize pollinator sampling techniques. This study investigated how sampling duration, weather conditions, and abundance of floral resources influenced the results of timed pollinator counts by repeatedly sampling the same pollinator assemblage in an Irish meadow. The likelihood of detection of Apis mellifera, Bombus spp, solitary bees, and Syrphidae was strongly associated with the density of floral units or floral cover in the observation plot. Also, even though protocol criteria restricted pollinator counts to the middle of the day and benevolent weather, pollinator counts were strongly influenced by factors such as cloud cover, light levels, wind speed and relative humidity. Increasing the duration of the timed counts from 5-minutes to 30-minutes considerably increased the probability of detection of each pollinator group. Additionally, the perceived diversity of the pollinator assemblage at the meadow was markedly affected by sampling duration and floral abundance. To improve the consistency or comparability of studies using timed pollinator counts, we recommend that criteria are set restricting surveys to narrow ranges of weather conditions and floral density when possible. Additionally, pollinator field investigations or monitoring programs would benefit from a systematic evaluation of how erroneous non-detection of target taxa can be reduced to acceptable levels by modifying sampling duration.

Mapping nectar-rich pollinator floral resources using airborne multispectral imagery

Wild pollinator numbers are known to be positively associated with amounts of flower-rich habitat at landscape level. Increasing floral resources can be particularly beneficial in relatively nectar-poor agricultural systems and having a baseline understanding of the temporal and spatial availability of resources can allow targeted habitat management. Very high-resolution remote sensing has potential to facilitate accurate mapping of fine-scale, within-habitat pollinator foraging resources, thereby allowing spatial and temporal gaps to be identified and addressed, improving predictions of pollinator numbers, and enabling remote monitoring of pollinator conservation measures.Concentrating on hedgerow and flower-rich field margins in a UK agricultural landscape, we showed that multispectral airborne imagery with 3 cm and 7 cm spatial resolutions can be used to classify five nectar-rich flowering plant species (Prunus spinosa, Crataegus monogyna, Rubus fruticosus, Silene dioica and Centaurea nigra) using a maximum likelihood classification algorithm. In 2019, we separately acquired 3 cm and 7 cm imagery for the months of March, May and July, respectively. Overall accuracies were above 90% for each month at both 3 cm and 7 cm resolutions (range 92.32%–98.72%), supporting previous research that suggests higher spatial resolutions do not necessarily lead to higher accuracies, as pixel variability is increased.Remaining challenges include determining which co-flowering species of similar colours in the visible range can be distinguished from one another within classifications and quantifying floral unit density from classifications so that the nectar sugar supply can be calculated. Nonetheless, we provided a prototype approach for mapping pollinator foraging resources in an agricultural context, which can be extended to other nectar-rich species. The foundation is set for developing a remote sensing pipeline that can provide valuable data on the availability of nectar-rich flowering plant species at different time-points throughout the year.

High flower richness and abundance decrease pollen transfer on individual plants in road verges but increase it in adjacent fields in intensively managed agroecosystems

Road verges can facilitate the movement of pollinators and pollen in intensively managed agroecosystems, reducing the negative impacts of fragmentation (i.e., isolation of wild pollinator communities) and enhancing the pollination service provided to wild plants. To assess the role of road verges in sustaining the pollination service to wild plants, we studied gardens consisting of two plant species arranged within sixteen road verges and their adjacent fields during two consecutive seasons in the Argentine Pampas. We assessed the influence of attributes of road verges on pollination service at different scales: road verges width, species richness of flowering plant, and flower abundance (patch scale), crops and successional pastures (adjacent land use scale), and landscape heterogeneity (landscape scale). We measured the pollination service provided to two species of potted plants (Hirschfeldia incana and Lobularia maritima) in three different ways: visitation rate, conspecific and heterospecific pollen transfer to stigmas, and distance of pollen transfer from a fixed source. The number of conspecific and heterospecific pollen grains deposited on stigmas decreased with an increased abundance of floral units in associated road verges, which is caused by a dilution effect on individual plant pollination. Also, the pollen transfer into adjacent fields decreased with an increased abundance of floral units in the nearby road verges, which is caused by a decrease of pollen spillover into adjacent crop fields. The visitation rate within adjacent fields increased with higher flowering plant species richness in associated road verges. Also, the number of conspecific pollen grains in the road verges adjacent to successional pastures increased with higher flowering plant species richness in road verges, which results in a concentration effect of pollinator visits and pollen transfer into road verges. We conclude that managing flower abundance and increasing flowering plant species richness in road verges are crucial practices for maintaining the pollination service of entomophilous plants in intensively managed agroecosystems.

Deep learning object detection to estimate the nectar sugar mass of flowering vegetation

Abstract Floral resources are a key driver of pollinator abundance and diversity, yet their quantification in the field and laboratory is laborious and requires specialist skills. Using a dataset of 25,000 labelled tags of fieldwork‐realistic quality, a convolutional neural network (Faster R‐CNN) was trained to detect the nectar‐producing floral units of 25 taxa in surveyors’ quadrat images of native, weed‐rich grassland in the United Kingdom. Floral unit detection on a test set of 50 model‐unseen images of comparable vegetation returned a precision of 90%, recall of 86% and F1 score (the harmonic mean of precision and recall) of 88%. Model performance was consistent across the range of floral abundance in this habitat. Comparison of the nectar sugar mass estimates made by the CNN and three human surveyors returned similar means and standard deviations. Over half of the nectar sugar mass estimates made by the model fell within the absolute range of those of the human surveyors. The optimal number of quadrat image samples was determined to be the same for the CNN as for the average human surveyor. For a standard quadrat sampling protocol of 10–15 replicates, this application of deep learning could cut pollinator‐plant survey time per stand of vegetation from hours to minutes. The CNN is restricted to a single view of a quadrat, with no scope for manual examination or specimen collection, though in contrast to human surveyors its object detection is deterministic and its floral unit definition is standardized. As agri‐environment schemes move from prescriptive to results‐based, this approach provides an independent barometer of grassland management which is usable by both landowner and scheme administrator. The model can be adapted to visual estimations of other ecological resources such as winter bird food, floral pollen volume, insect infestation and tree flowering/fruiting, and by adjustment of classification threshold may show acceptable taxonomic differentiation for presence–absence surveys.

Floral trait functional diversity is related to soil characteristics and positively influences pollination function in semi-natural grasslands

Semi-natural grasslands are threatened habitats providing many ecosystem services, such as climate regulation or water erosion control. Factors affecting the vegetative trait diversity of their plant communities are well studied, but those affecting their floral diversity are not. Local factors, such as land-use intensification and soil characteristics, can greatly influence floral trait diversity in semi-natural grasslands, which in turn can influence pollination function. We selected 16 semi-natural grasslands in France along a local land-use intensification gradient. Floral functional diversity indices were calculated from measurements of five floral traits known to influence interactions with pollinators: flower area, flowering height, floral reflectance, nectar tube depth and nectar sugar production per floral unit. Using linear mixed models, we found a negative influence of phosphorus soil content, and a positive influence of a composite soil variable including soil texture, organic carbon and total nitrogen soil content, on floral functional diversity. However, local land-use intensification did not influence floral functional diversity. Moreover, our results showed a positive relation between floral functional diversity and plant-pollinator interaction frequency as a proxy of pollination function. More specifically, we found a positive influence of the nectar resource diversity (i.e. the variability in production of nectar sugar by flowers) on plant-pollinator interaction frequency. These results, based on a correlative approach and functional diversity indices as measure of functional complementarity, suggest that the diversity of floral traits may promote niche partitioning of pollinators and pollination function approximated by plant-pollinator interaction frequency, and highlight the main role of nectar in this process.

Plant-pollinator interactions on green roofs are mediated by substrate characteristics and plant community composition

Green roofs can support pollinator communities in cities. However, little is known about the influence of green roof characteristics such as substrate and vegetation type on the abundance and diversity of attracted pollinators. Here we aimed to assess how green roof design impacts their attractiveness to pollinators. Using mesocosms on a rooftop in Paris (France), we studied the impact of two substrate types, two substrate depths (10 and 30 cm) and either monocultures or mixtures of 5 plant species on plant pollinator interactions. In the case of mixtures, we also tested the effect of substrate type (natural soil vs. artificial substrate). We counted the number of floral units and recorded the visits by pollinators once a week from mid-June to mid-August. The pollinator assemblage visiting plant communities included 4 functional groups of pollinators: domesticated honey bees, bumble bees, solitary bees and syrphid flies. Effects of treatments on pollinator community composition were variable and plant species dependent. Deep monoculture treatments resulted in the highest number of floral units and visits. Although plants grown on natural soil had less floral units than on artificial substrate, both treatments resulted in a similar number of visits. This paper provides evidence that plant-pollinator interactions on green roofs are modulated by substrate type, substrate depth and plant community. We suggest that combining plant species with diverse flowering morphologies and phenologies can enhance pollinator diversity. When possible, increasing substrate depth can result in higher levels of attractiveness.

The 'Male Flower' of Ricinus communis (Euphorbiaceae) Interpreted as a Multi-Flowered Unit.

One of the most exciting questions in botany refers to the nature of the angiosperm flower. While most flowering structures are easily identified as flowers, there are few examples lying in-between flowers and inflorescences. Such an example is the staminate unit (‘male flower’) in Ricinus communis (Euphorbiaceae) famous for its branched ‘staminal trees.’ The units were controversially interpreted in the past. Today, they are seen as flowers with multiple branched stamen-fascicles. In the present paper, the recently described floral unit meristem is used to reinterpret the staminate units in Ricinus. This meristem shares almost all characteristics with a flower meristem, but differs from it in the number of fractionation steps resulting in multi-flowered units. Reinvestigation of the development confirms previous studies illustrating up to six fractionation steps before the meristem merges into anther-formation. Fractionation starts early at a naked meristem, covers simultaneously its whole surface, shows an all-side instead of unidirectional splitting pattern and continues repeatedly. Based on the present knowledge, it is plausible to interpret the ‘male flower’ as a floral unit with multiple staminate flowers each reduced to a single anther. This interpretation is in accordance with the many examples of reduced flowers in the Euphorbiaceae.

Drought reduces floral resources for pollinators.

Climate change is predicted to result in increased occurrence and intensity of drought in many regions worldwide. By increasing plant physiological stress, drought is likely to affect the floral resources (flowers, nectar and pollen) that are available to pollinators. However, little is known about impacts of drought at the community level, nor whether plant community functional composition influences these impacts. To address these knowledge gaps, we investigated the impacts of drought on floral resources in calcareous grassland. Drought was simulated using rain shelters and the impacts were explored at multiple scales and on four different experimental plant communities varying in functional trait composition. First, we investigated the effects of drought on nectar production of three common wildflower species (Lathyrus pratensis, Onobrychis viciifolia and Prunella vulgaris). In the drought treatment, L.pratensis and P.vulgaris had a lower proportion of flowers containing nectar and O.viciifolia had fewer flowers per raceme. Second, we measured the effects of drought on the diversity and abundance of floral resources across plant communities. Drought reduced the abundance of floral units for all plant communities, irrespective of functional composition, and reduced floral species richness for two of the communities. Functional diversity did not confer greater resistance to drought in terms of maintaining floral resources, probably because the effects of drought were ubiquitous across component plant communities. The findings indicate that drought has a substantial impact on the availability of floral resources in calcareous grassland, which will have consequences for pollinator behaviour and populations.