A dataset of the flowering plants (Angiospermae) in urban green areas in five European cities

Data in Brief 37 (2021) 107243 Contents lists available at ScienceDirect Data in Brief journal homepage: www.elsevier.com/locate/dib Data Article A dataset of the flowering plants (Angiospermae) in urban green areas in five European cities Joan Casanelles-Abella a , b , ∗, David Frey a , Stefanie Müller a , c , Cristiana Aleixo d , Marta Alós Ortíe , Nicolas Deguines f , g , Tiit Hallikma e , Lauri Laanisto e , Ülo Niinemets e , Pedro Pinho d , Roeland Samson h , Lucía Villarroya-Villalba a , Marco Moretti a a Biodiversity and Conservation Biology, Swiss Federal Research Institute WSL, Birmensdorf, Switzerland b Landscape Ecology, Institute of Terrestrial Ecosystems, ETH Zürich, Zürich, Switzerland c Department of Evolutionary Biology and Environmental Studies, University of Zürich, Zürich, Switzerland d Centre for Ecology, Evolution and Environmental Changes (cE3c), Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal e Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Tartu, Estonia f Université Paris-Saclay, CNRS, AgroParisTech, Ecologie Systématique Evolution, Orsay, France g Laboratoire Ecologie et Biologie des Interactions, Equipe Ecologie Evolution Symbiose, Université de Poitiers, UMR CNRS 7267, France h Lab of Environmental and Urban Ecology, Research Group Environmental Ecology & Microbiology (ENdEMIC), Dept. Bioscience Engineering, University of Antwerp, Antwerp, Belgium a r t i c l e i n f o Article history: Received 15 March 2021 Revised 14 June 2021 Accepted 18 June 2021 Available online 25 June 2021 a b s t r a c t This article summarizes the data of a survey of flowering plants in 80 sites in five European cities and urban agglomerations (Antwerp, Belgium; greater Paris, France; Poznan, Poland; Tartu, Estonia; and Zurich, Switzerland). Sampling sites were selected based on a double orthogonal gradient of size and connectivity and were urban green areas (e.g. parks, cemeteries). To characterize the flowering plants, two sampling methodologies were applied between April and July 2018. First, a floristic inventory of the occurrence of all flowering plants in the five cities. Second, flower counts in sampling plots of standardized size (1 m 2 ) only in Zurich. ∗Corresponding author. E-mail address: [email protected] (J. Casanelles-Abella). Social media: (J. Casanelles-Abella), (N. Deguines), (L. Laanisto), (R. Samson), (L. VillarroyaVillalba) https://doi.org/10.1016/j.dib.2021.107243 2352-3409/© 2021 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ ) 2 J. Casanelles-Abella, D. Frey and S. Müller et al. / Data in Brief 37 (2021) 107243 Keywords: Urban biodiversity Urban green spaces Urban flora Plants Gardening Urban green infrastructure Plant traits Floral traits Fragmentation We sampled 2146 plant species (contained in 824 genera and 137 families) and across the five cities. For each plant species, we provide its origin status (i.e. whether the plants are native from Europe or not) and 11 functional traits potentially important for plant-pollinator interactions. For each study site, we provide the number of species, genera, and families recorded, the Shannon diversity as well as the proportion of exotic species, herbs, shrubs and trees. In addition, we provide information on the patch size, connectivity, and urban intensity, using four remote sensing-based proxies measured at 100and 800-m radii. ©2021 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ ) Specifications Table Subject Ecology, Nature, and Landscape Conservation. Specific subject area Urban ecology Type of data Table Fig. How data were acquired Floristic inventories and standardized floral counts. Satellite data. Data format Raw and aggregated Parameters for data collection Sites were selected from the European Urban Atlas, using the features mapped as green areas. Sites were chosen following an orthogonal gradient of patch size and connectivity inferred with the proximity index. We selected 32 sites in Zurich, Switzerland, and 12 sites in each of the remaining four cities (i.e. Antwerp, Paris, Poznan and Tartu). Description of data collection We applied two sampling methodologies inside of buffers of 100 m radius: 1) a floristic inventory of the occurrence of all flowering plants of potential interest for pollinators performed in the five cities, and 2) flower counts in sampling plots of standardized size (1 m 2 ) done only in Zurich. Sites were visited on three occasions between April and July 2018. The duration of each visit was restricted to a maximum of 2.5 h. Data source location City of Antwerp, Belgium; 51 °15  N, 4 °24  E Greater Paris, France; 48 °51  N, 8 °05  E City of Poznan, Poland; 52 °24  N, 16 °55  E City of Tartu, Estonia; 58 °22  N, 26 °43  E City of Zurich, Switzerland; 47 °22  N, 8 °33  E Data accessibility Repository name: Envidat Data identification number: doi:10.16904/envidat.210 Direct URL to data: https://www.envidat.ch/dataset/ floweringplantsangiospermaeinurbangreenareasinfiveeuropeancities File 1: Floral_1_occurrence.csv contains the list of plant species sampled in the five cities during the different sampling periods. File 2: Floral_2_counts.csv contains the floral units, mean number of flowers per floral units and the floral abundance of the different plants counted in quadrats in the study sites in Zurich during four sampling periods. File 3: Floral_traits.csv contains the trait values extracted from the literature for the sampled plants. Value of the Data • The dataset describes the diversity, occurrence, and floral counts of a large number of flowering plant families sampled in a standardized way in different types of public and private green areas in European cities, and with a high taxonomic resolution. J. Casanelles-Abella, D. Frey and S. Müller et al. / Data in Brief 37 (2021) 107243 3 • The data contribute characterizing European urban floras, derive taxonomic, phylogenetic and trait diversity patterns, and perform comparative studies among different cities, different types of urban green areas and in fragmentation studies. • The data can be used to characterize the available food resources of other trophic levels, particularly pollinators, and species interactions. • The data on floral counts can be combined with metrics on nectar and pollen content to obtain estimates of resources quality (e.g. as done in [1] ) • The methodology for collecting the data can be applied in further studies aiming to characterize plant resources in one or more urban ecosystems in a standardized way. 1. Data Description The paper presents the data of a plant survey in urban green areas from five European cities and urban agglomerations (Antwerp, Belgium; greater Paris, France; Poznan, Poland; and Zurich, Switzerland). 80 sites were selected (32 in Zurich and 12 in each of the remaining four cities, see Fig. 1 ) according to an orthogonal gradient of patch size and connectivity (see Section 2.2 ), representing common public urban green areas such as parks, cemeteries and gardens. To characterize the flowering plants, we sampled plants during four (for Zurich) and three (for Antwerp, Paris, Poznan and Tartu) sampling periods during the year 2018. The sampling was performed in (1) end of April (only for Zurich), (2) end of May, (2) end of June and (3) end of July. The sampling consisted in two methodologies. First, a floristic inventory of the occurrence of all flowering plants inside buffers of 100 m radius (see Fig. 1 ) in the study sites of the five cities. Second, flower counts of defined floral units ( Table 1 ) in sampling plots of standardized size (1 m 2 ) distributed inside buffers of 100 m radius (see Fig. 1 ) done only in Zurich. The 100 m radius buffer was defined from existing installed trap-nests place to sample cavity-nesting bees and wasps ( Fig. 1 ). For each of the 2146 plant species recorded we show in what cities it was recorded ( Supplementary material, Table A1 ). Furthermore, we provide information on 11 traits of potential interest to study plant-pollinator interactions ( Table 2 ) that are the flowering duration, flowering start, growth form, inflorescence type, plant height, floral rewards in the form of nectar, oil and pollen, structural blossom class and floral symmetry based on bibliographic information. Additionally, we documented the origin status of all the sampled plant species, that is, whether or not they are native from Europe. We computed the species, genera, and family richness for each site ( Table 3 and Fig. 2 ) and the composition of plant families of the species sampled in each city ( Fig. 3 ). Moreover, we computed the proportion of exotic species, as well as the proportion of trees, shrubs, and herbs for each site and city ( Table 3 and Fig. 4 ). In addition, we show the frequency distribution of floral counts ( Fig. 5 ) and the composition of plant genera in the flower abundance ( Fig. 6 ) in the city of Zurich. We provide information on the study site features including the city, their size, connectivity, and urban intensity inferred using a set of remote sensing-based proxies on soil, grey infrastructure, and vegetation, including the Second Brightness Index (BI2), the Color Index (CI), the Urban Index (UI), and the Normalized Difference Vegetation Index (NDVI) within a 100 and 800 m buffer centered in the centroid of the urban green area ( Table 4 ). The data are part of the interdisciplinary research project BioVeins investigating different aspects of urban biodiversity and ecosystem services in urban green areas in European cities ( https://www.biodiversa.org/1012 ). The data can be linked to other taxonomic groups such as nocturnal insects and bats [2] , sampled in the same study locations and during the same period. The raw data are available from the repository Envidat [3] with the DOI doi:10.16904/envidat.210. 4 J. Casanelles-Abella, D. Frey and S. Müller et al. / Data in Brief 37 (2021) 107243 Table 1 Definition of the flower units and calculation of the floral abundance. For each floral unit type, we show the plant taxa included and how the floral abundance was calculated. For specific floral unit types (i.e. capitula in Dipsacoidae, compound cymes, corymb, panicles, racemes and umbels) we estimated the number of flowers per floral unit by counting all the flowers in seven floral units and computing the mean. Ditto = the same again. Floral unit definition Plant taxa Estimation number of flowers within a floral unit (Nf) Floral abundance (Fa) Single flowers Acanthaceae, Alismataceae, Amaranthaceae, Anacardiaceae, Apocynaceae, Asparagaceae, Balsaminaceae, Begoniaceae, Boraginaceae, Brassicaceae, Campanulaceae (except Phyteuma spp.), Caprifoliaceae (except Dipsacoideae), Caryophyllaceae, Celastraceae, Cistaceae, Cleomaceae, Convolvulaceae, Crassulaceae, Cucurbitaceae, Cytisus spp., Geraniaceae, Hypericaceae, Iridiaceae, Lamiaceae, Lathyrus spp., Linaceae, Lythraceae, Magnoliaceae, Malvaceae, Onargaceae, Orchidaceae, Orobanchaceae, Oxalidaceae,Papaveraceae, Phrymaceae, Plantaginaceae (except Plantago spp.), Polemoniaceae, Polygonaceae, Portulacaceae, Primulaceae, Ranunculaceae, Resedaceae, Rhododendron spp., Rosaceae (except Filipendula ulmaria, Sanguisorba spp., Spiraea spp.), Rutaceae, Saxifragaceae, Spartium spp., Solanaceae, Scrophulariaceae (except Buddleja davidii ), Tropeolaceae, Verbenaceae, Violaceae, Xanthorrhoeaceae Not applicable F a =  ( floral units ) Single capitulum (in Dipsacoideae) Dipsacoideae Estimation in seven different floral units Nf = mean of the seven counts Fa =  (( floral units ) ×Nf ) Single compound cyme Centranthus spp. Ditto Ditto Single corymb Adoxaceae, Cornaceae Ditto Ditto Single panicle Sapindaceae ∗, Buddleja davidii, Galium spp. , Filipendula ulmaria, Sherardia arvensis, Spiraea spp, Syringa vulgaris Ditto Ditto ( continued on next page ) J. Casanelles-Abella, D. Frey and S. Müller et al. / Data in Brief 37 (2021) 107243 5 Table 1 ( continued ) Floral unit definition Plant taxa Estimation number of flowers within a floral unit (Nf) Floral abundance (Fa) Single raceme Fabaceae ∗(except Cytisus spp., Lathyrus spp., Spartium spp.), Hedera helix, Ligustrum spp., Vitaceae Ditto Ditto Single secondary umbell Apiaceae Ditto Ditto Single umbell Allium spp. Ditto Ditto Single capitulum (in Asteraceae) Asteraceae Not estimated F a =  ( floral units ) Single catkin Betulaceae ∗, Fagaceae ∗, Salicaceae ∗Not estimated Ditto Single corymb & single cyme in Hydragea spp. Hydrangea spp. Not estimated Ditto Single cyme with cyathia Euphorbia spp. Not estimated Ditto Single dense cluster Sanguisorba Not estimated Ditto Single spike (in Plantago spp. & Tamarix spp.) Plantago spp. , Tamarix spp. Not estimated Ditto ∗Observation of the tree canopy and the floral counts of the woody species in these families were done from the ground and are a rough estimate. 6 J. Casanelles-Abella, D. Frey and S. Müller et al. / Data in Brief 37 (2021) 107243 Fig. 1. Maps of the study sites in each of the five cities (Antwerp, Greater Paris, Poznan, Tartu and Zurich) and an example of how the sampling was conducted. For the site Zu006 (located in Zurich), we show the trap-nest location (green dot), the 100 m radius buffer around it and the 16 cells dividing the buffer. 2. Experimental Design, Materials and Methods 2.1. Data source The data was acquired in the European cities of Antwerp, Belgium (51 °15  N, 4 °24  E), Greater Paris, France (48 °51  N, 8 °05  E), Poznan, Poland (52 °24  N, 16 °55  E), Tartu, Estonia (58 °22  N, 26 °43  E), Zurich, Switzerland (47 °22  N, 8 °33  E). The climate of Antwerp is oceanic, the climate of Paris is temperate, the climate of Poznan is continental, the climate of Tartu is mild continental boreal and the climate of Zurich is mild continental temperate. The agglomeration of greater J. Casanelles-Abella, D. Frey and S. Müller et al. / Data in Brief 37 (2021) 107243 7 Table 2 List of the 11 traits included. For each trait together, there is a description, the taken values, and references of the sources used to build the trait table. See also Section 2.7 Traits. Trait Description Values References Flowering duration Number of months a plant species flower. 1–12 [4–8] Flowering start The month the blossom of a plant species begins to flower. 1–12 [4–8] Growth form Classification of plant species in four broad growth form categories. Herb Shrub Tree Climber [6 , 9–11] Inflorescence type Determines whether the blossom is a single flower or an inflorescence. With inflorescence Without inflorescence [4–6 , 12] Plant height (m) Measure of the height of a plant species in meters. [4 , 6 , 9 , 10] Pollination mode Definition whether a plant species is biotically or abiotically pollinated. Biotic Abiotic [6 , 9] Rewards: nectar Describes whether the plant provides nectar resources. Absent Present [4 , 5 , 10 , 13–16] Rewards: oils Describes whether the plant provides oils. Absent Present [4 , 5 , 10 , 13–16] Rewards: pollen Describes whether the plant provides pollen resources. Absent Present [4 , 5 , 10 , 13–16] Structural Blossom Class Describing the shape of the blossom of the plant species. Dish-bowl Stalk-disk Bell trumpet Brush Gullet Flag Tube Adapted from [17] Symmetry Describes the number of axes of reflection of a flower of a plant species. The value was derived from the structural blossom class No symmetry Zygomorph Actinomorph Paris is the most populated one in Europe with more than seven million inhabitants (2.18 million inhabitants only in the city of Paris [19] ). Antwerp has the second highest population (0.53 million inhabitants [19] ) followed by Poznan (0.53 million inhabitants [19] ), Zurich (0.4 million inhabitants [19] ), and Tartu (0.09 million inhabitants [19] ). 2.2. Site selection We selected patches among urban green areas mapped and defined in the European Urban Atlas [see 20 ], which includes mostly public urban green areas in the form of parks, cemeteries, and ruderal patches. We used an orthogonal gradient of patch size (area in m2) and connectivity. Connectivity was calculated using the Proximity Index (PI) which considers the area and the distance to all nearby patches with a favorable habitat, within a given search radius (in our case 50 0 0 m), and is defined as: P I =  n s =1 a ijs h 2 ijs 8 J. Casanelles-Abella, D. Frey and S. Müller et al. / Data in Brief 37 (2021) 107243 Table 3 Summary statistics of the plants recorded. For each of the 80 study sites in the five cities, we provide the number of species ( N species ), genera ( N genera ), families ( N families ), the value of the Shannon diversity index ( H’ ), and the proportion of herbs ( P herbs ), shrubs ( P shrubs ), trees ( P trees ), and exotic species ( P exotic ). H’ was calculated using the frequency of each plant species, obtained as the number of cells from the total 16 where the plant was found. The data are based on floristic inventories in the study sites. The data are plotted in Fig. 1 - 2 . Site codes represent the study sites shown in Fig. 1 . Note that the statistic does not include species in the families Cyperaceae, Juncaceae and Poaceae. The coordinates of the sites are provided in Table 4 . City Site N species N genera N families H’ P herbs P shrubs P trees P exotic Antwerp An011 91 87 41 4.75 0.72 0.13 0.13 0.34 An016 44 39 22 3.83 0.74 0.17 0.06 0.13 An020 61 57 33 4.3 0.7 0.16 0.12 0.27 An056 52 44 26 4.01 0.86 0.09 0.04 0.15 An057 27 24 15 3.3 0.7 0.11 0.15 0.3 An062 65 53 25 4.16 0.79 0.06 0.09 0.36 An068 60 60 36 4.2 0.61 0.16 0.16 0.48 An073 64 52 29 4.26 0.66 0.17 0.14 0.31 An082 61 56 29 4.16 0.64 0.17 0.14 0.39 An088 47 39 24 3.89 0.65 0.2 0.08 0.33 An092 53 45 24 4.03 0.77 0.11 0.09 0.23 An102 85 73 36 4.55 0.77 0.13 0.08 0.32 Paris Pa013 191 138 51 5.3 0.72 0.18 0.08 0.33 Pa191 148 124 51 5.11 0.7 0.17 0.11 0.44 Pa245 102 90 40 4.71 0.73 0.14 0.11 0.21 Pa265 91 79 39 4.62 0.71 0.19 0.09 0.38 Pa269 171 146 56 5.19 0.65 0.22 0.11 0.36 Pa282 83 68 34 4.6 0.7 0.07 0.21 0.22 Pa295 125 112 54 4.95 0.69 0.19 0.1 0.43 Pa398 1167 555 100 7.07 0.83 0.13 0.02 0.42 Pa418 85 75 36 4.48 0.76 0.16 0.05 0.41 Pa492 91 74 36 4.58 0.82 0.09 0.09 0.2 Pa535 122 110 46 4.91 0.77 0.11 0.1 0.39 Pa573 52 51 32 4.08 0.5 0.29 0.17 0.39 Poznan Po001 45 43 19 3.91 0.84 0.12 0.04 0.28 Po037 12 24 16 3.26 0.62 0.15 0.23 0.35 Po059 56 56 28 4.13 0.76 0.13 0.11 0.24 Po137 37 29 14 3.64 0.84 0.13 0.03 0.24 Po179 36 32 19 3.66 0.77 0.05 0.16 0.18 Po183 75 67 28 4.41 0.74 0.15 0.09 0.28 Po210 35 33 18 3.69 0.92 0.03 0.05 0.12 Po227 58 65 32 4.28 0.72 0.1 0.16 0.38 Po267 38 42 23 3.91 0.8 0.02 0.18 0.16 Po348 63 52 24 4.2 0.72 0.15 0.11 0.3 Po406 44 42 18 3.89 0.84 0.06 0.06 0.24 Po423 72 66 31 4.39 0.79 0.11 0.1 0.2 Tartu Ta008 87 73 31 4.53 0.89 0.06 0.03 0.29 Ta013 59 48 24 4.14 0.87 0.02 0.08 0.11 Ta025 51 45 21 3.95 0.92 0.02 0.06 0.08 Ta033 48 40 17 3.85 0.98 0 0.02 0.11 Ta040 100 86 35 4.63 0.89 0.04 0.06 0.24 Ta047 64 57 29 4.22 0.85 0.03 0.07 0.1 Ta057 79 66 29 4.48 0.91 0.02 0.05 0.22 Ta064 41 38 20 3.81 0.89 0.02 0.09 0.09 Ta102 46 43 18 3.95 0.94 0.02 0.04 0.06 Ta104 51 43 19 3.99 0.91 0.04 0.06 0.07 Ta110 78 63 28 4.37 0.92 0.05 0.02 0.19 Ta125 59 60 30 4.29 0.87 0.03 0.07 0.21 Zurich Zu006 210 143 57 5.39 0.8 0.12 0.06 0.34 Zu007 131 100 35 4.91 0.9 0.04 0.05 0.24 Zu015 730 386 99 6.6 0.83 0.11 0.05 0.41 ( continued on next page ) J. Casanelles-Abella, D. Frey and S. Müller et al. / Data in Brief 37 (2021) 107243 9 Table 3 ( continued ) City Site N species N genera N families H’ P herbs P shrubs P trees P exotic Zu018 210 142 53 5.42 0.74 0.13 0.1 0.3 Zu033 279 187 58 5.68 0.75 0.12 0.1 0.33 Zu039 144 115 45 5.04 0.81 0.09 0.08 0.24 Zu057 261 187 62 5.65 0.67 0.15 0.15 0.32 Zu062 144 115 47 4.99 0.74 0.16 0.1 0.32 Zu067 168 128 50 5.21 0.78 0.1 0.07 0.33 Zu080 110 88 40 4.73 0.82 0.09 0.09 0.15 Zu082 212 158 56 5.42 0.77 0.09 0.11 0.31 Zu087 106 85 32 4.71 0.77 0.13 0.07 0.25 Zu094 254 185 62 5.6 0.84 0.08 0.05 0.28 Zu105 126 86 32 4.87 0.79 0.1 0.1 0.1 Zu113 158 109 44 5.11 0.75 0.15 0.09 0.19 Zu119 136 95 36 4.93 0.85 0.05 0.1 0.12 Zu126 223 171 56 5.48 0.81 0.12 0.06 0.33 Zu133 238 162 57 5.51 0.76 0.15 0.07 0.33 Zu141 112 114 41 5.21 0.79 0.12 0.08 0.21 Zu154 201 136 48 5.3 0.81 0.1 0.06 0.25 Zu155 245 81 27 4.8 0.87 0.07 0.05 0.12 Zu158 149 132 45 5.34 0.85 0.06 0.06 0.21 Zu173 191 168 51 5.55 0.79 0.12 0.07 0.32 Zu179 180 110 45 5.06 0.83 0.13 0.02 0.28 Zu904 172 131 45 5.19 0.88 0.04 0.06 0.27 Zu905 161 124 46 5.1 0.83 0.09 0.06 0.26 Zu906 237 156 53 5.49 0.87 0.07 0.04 0.29 Zu907 205 146 46 5.35 0.79 0.13 0.001 0.28 Zu908 182 122 51 5.26 0.74 0.13 0.11 0.27 Zu910 220 159 57 5.47 0.74 0.12 0.09 0.28 Zu911 213 136 51 5.4 0.83 0.09 0.06 0.22 Zu912 113 86 41 4.76 0.67 0.16 0.14 0.25 Where a ijs is the area (m 2 ) of a patch ijs within specified neighbourhood (m) of a patch ij , and h 2 ijs is the distance (m) between the patch ijs , based on patch edge-to-edge distance. Thus, the PI measures the degree of patch isolation, with highest values given to less isolated patches. We considered as favourable habitat all patches with high probability of having trees (besides urban green areas, also forest and low density urban, with less than 30% impervious surface, see [20] ). The search radius was set to 5 km from each focal patch, the maximum possible with the available cartography. In fact, lower buffer values (from 500 m onwards) did not greatly change the PI values, because the distances are squared, thus greatly limiting the impact of patches beyond a certain distance. To select patches using the orthogonal design, all possible patches were classified in six size classes and six classes of the PI (36 possible combinations). Within these combinations, patches were selected randomly (random stratified sampling design). Due to resource limitations, we only used 1/3 of the possible combinations in Antwerp, Paris, Poznan, and Tartu (maximizing the gradient) and the full range of combinations in Zurich (32 combinations, the other combinations were not available in the city). This resulted in the final selection of 80 sites ( Fig. 1 ): 32 in Zurich and 12 in each of the remaining cities. Sites were selected keeping a minimum distance of 500 m (except for two sites in Zurich selected by their position in the patch and connectivity gradient, separated by 260 m). Median distance to the nearest site was 6610 m in Antwerp (minimum = 966 m, maximum = 15,375 m), 7852 m in Paris (minimum = 721 m, maximum = 31,891 m), 3912 m in Poznan (minimum = 1630 m, maximum = 17,189 m), 3913 m in Tartu (minimum = 788 m, maximum = 10,520 m), and 4299 m in Zurich (minimum = 371 m, maximum = 10,560 m). Furthermore, pairwise distances among sites were in 99% of the cases larger than 750 m. 16 J. Casanelles-Abella, D. Frey and S. Müller et al. / Data in Brief 37 (2021) 107243 Fig. 5. Histogram of the floral counts in the city of Zurich. Floral abundance, shown in the X axis, is calculated as the sum of all the floral units (see Table 1 for the definitions) in all the quadrats for a given site and sampling period, giving a total N of 128 (32 sites x 4 sampling periods). The dashed vertical line represents the median floral abundance and the straight vertical line the mean floral abundance recorded. total duration of each sampling in a site was restricted to about 2.5 h to standardize sampling effort. Note that the late winter and early spring flowers were missed (e.g. Crocus spp., Galanthus spp.). The species, genus, and family richness of each sampling site are given in Table 3 . The list of all taxa and the number of observations per taxon are given in the Supplementary material, Table A1 . 2.5. Floral counts on standardized plots We calculated the floral abundance in a site and sampling period by using 1 m 2 quadrats randomly distributed inside the 100 m buffer. The number of quadrats was determined according to the amount of green areas in each buffer, with a minimum of seven quadrats, when less than 20% of the buffer was covered by green areas, and a maximum of 15 quadrats, when more than 90%. To obtain the floral abundance, we first defined a set of floral units on where we classified the different plant species (see Table 1 ). The floral abundance of each floral unit type was calculated in the following way. For single flowers, the floral abundance was obtained by summing all the individual flowers ( Table 1 ). For single capitula (in Dipsacoideae species), single compound cymes, single corymbs, single panicles, single racemes, single umbels, we took seven different floral units, counted all the flowers and computed a mean number of flowers per floral unit. The mean number of flowers per floral unit was calculated separately for each site and sampling period. The floral abundance was then obtained by multiplying the number of floral units and the mean number of flowers per floral unit (see Table 1 ). Finally, for single capitula (in Asteraceae), single catkins, single corymbs or cymes in the Euphorbia genus, single dense clusters (including only Sangisorba spp.) and single spikes (including the genus Plantago spp. and J. Casanelles-Abella, D. Frey and S. Müller et al. / Data in Brief 37 (2021) 107243 17 Fig. 6. Barplot of the percentage of plant genera in the floral abundance counted in Zurich. Only genera containing more than 1% of the species sampled in all the study sites are shown separately. The remaining genera are grouped into the category “Other genera” (light gray) and the exact number (272) is provided at the top of the bar. Note that the families Cyperaceae, Juncaceae and Poaceae were not included in the sampling. Tamarix spp.) the floral abundance was computed by summing only the number of floral units, that is, we did not estimate a mean number of flowers per floral unit. 2.6. Taxonomic treatment Taxonomy assignment largely followed the criteria of Checklist of the National Data and Information Centre of the Swiss Flora [27] , together with The World Flora Online database [28] , and other resources, e.g. RHS Dictionary of Gardening [16] . Varieties, taxa within species complexes, and cultivars were mostly grouped into aggregates (e.g. Taraxacum officinale aggr.) or left at the genus level (e.g. Leucanthemum sp.) without further distinction. 2.7. Traits We aimed to select important determinants of plant-pollinator interactions. We developed a data set of 11 traits (see Table 2 ) for 2313 plant species. We used 11 functional traits including start and duration of the flowering period, growth type, inflorescence type, pollination mode, blossom class, symmetry, plant height and the presence of rewards in the form of pollen, nectar and oils. Additionally, we included the origin of the plant species, which are no functional traits per se. For functional traits, we used as main sources the TRY plant trait database [10] , the national data, and information centre for the Swiss flora [6] , the Bundesamt für Naturschutz (BfN) 18 J. Casanelles-Abella, D. Frey and S. Müller et al. / Data in Brief 37 (2021) 107243 [7] , Faegri and van der Pijl [17] , Frey and Moretti [9] , Missouri Botanical Garden Plant Finder [5] , Plants For A Future [4] , Plants of the World Online [12] , and BiolFlor [8] . Regarding the origin status of the plant species, a species was considered to be native when its origin was Europe and exotic if it originated elsewhere. To document the origin status of each plant species, we used the Global Biodiversity Information System [29] . Cultivar groups not derived from native plants were considered to be alien. The start and duration of the flowering period are given in months. For exotic plants from the Southern hemisphere, we do not provide information on the phenology. We defined the pollination mode for each species, based on Frey and Moretti [9] . Here, we distinguished whether a species is biotically or abiotically pollinated, i.e., mainly either by insects (entomophilous) or by wind (anemophilous). Concerning growth form, we defined four broad categories, that is, tree, shrub, herb, and climber. Trees included woody species typically classified as phanaerophytes, including species described as small trees or tall shrubs (e.g. Crataegus spp., Ligustrum spp.). Shrubs included mostly chamaephytes. Herbs included all herbaceous plants regardless of their height or growth form. Finally, climbers included woody and non-woody epyphites such as lianas and vines. The inflorescence types considered are the same as the ones in the floral counts (see Supplementary material, Table A1 ). We considered the type of structural blossom classes according to Faegri and van der Pijl [17] . Concerning symmetry, each plant was classified in three main categories of actinomorphy (two or more axis of symmetry), zygomorphy (one axis of symmetry) or without symmetry. Finally, for the rewards, we reported whether the plant species had been shown to provide floral resources in the form of nectar, oil and pollen. CRediT Author Statement Joan Casanelles-Abella: Conceptualisation, Methodology, Investigation, Validation, Data curation, Writing Original draft, Writing Review & Editing, Formal analysis, Project administration; David Frey: Methodology, Validation, Resources, Data curation, Writing Review & Editing; Stefanie Müller: Conceptualisation, Methodology, Investigation, Data curation, Writing Review & Editing; Cristiana Aleixo: Investigation, Data curation, Resources, Writing Review & Editing; Marta Alós Ortí: Investigation, Writing Review & Editing; Nicolas Deguines: Investigation, Validation, Writing Review & Editing; Tiit Hallikma: Investigation, Validation, Writing Review & Editing; Lauri Laanisto: Methodology, Writing Review & Editing; Ülo Niinemets: Funding acquisition, Writing Review & Editing; Pedro Pinho: Funding acquisition, Methodology, Investigation, Data curation, Resources, Writing Review & Editing; Roeland Samson: Funding acquisition, Methodology; Lucía Villarroya-Villalba: Investigation, Validation, Writing Review & Editing; Marco Moretti: Funding acquisition, Conceptualisation, Methodology, Writing Review & Editing, Supervision, Project administration. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships which have or could be perceived to have influenced the work reported in this article. Acknowledgments This research was supported by the Swiss National Science Foundation (project 31BD30_172467) within the program ERA-Net BiodivERsA project “BioVEINS: Connectivity of green and blue infrastructures: living veins for biodiverse and healthy cities” (H2020 BiodivERsA32015104). Pedro Pinho was supported by the FCT (UIDB/00329/2020). We thank the J. Casanelles-Abella, D. Frey and S. Müller et al. / Data in Brief 37 (2021) 107243 19 field technicians Piotr Kazimirski, Laure-Anne Frank and Emeline Klimczak. We thank Simone Fontana, Jordi Bosch, and Laura Roquer for their input developing the methodology. We thank the municipalities of Antwerp, Greater Paris, Poznan, Tartu, and Zurich for their engagement on the project BioVEINS. 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