Conceived and designed the experiments: SEA VS LC. Performed the experiments: LC. Analyzed the data: SEA SF. Contributed reagents/materials/analysis tools: VS LC. Wrote the paper: SEA. Designed the database format, supervised the programming, organised the infrastructure to launch the database online, collated data: SEJA. Created all the website programming and developed the database structure: SF. Provided datasets for the database and helpful discussion: VS. Provided discussion and support during programming and development: PWM.
Current address: Natural Resources Institute, University of Greenwich, Chatham Maritime, United Kingdom
The authors have declared that no competing interests exist.
Flower colour is of great importance in various fields relating to floral biology and pollinator behaviour. However, subjective human judgements of flower colour may be inaccurate and are irrelevant to the ecology and vision of the flower's pollinators. For precise, detailed information about the colours of flowers, a full reflectance spectrum for the flower of interest should be used rather than relying on such human assessments.
The Floral Reflectance Database (FReD) has been developed to make an extensive collection of such data available to researchers. It is freely available at
The Floral Reflectance Database is a valuable new tool for researchers interested in the colours of flowers and their association with pollinator colour vision, containing raw spectral reflectance data for a large number of flower species.
Flower colour and pigmentation are of interest to researchers in areas of both developmental biology and pollination ecology
Samples originate from Germany and Brazil respectively. The reflectance is the proportion of light at each wavelength reflected by the sample.
We have developed the Floral Reflectance Database (FReD) to provide free, searchable access to reflectance spectra of a large number of flowers, thus making available extensive information about flower colour that is not inherently human-biased and which can be used when considering the interactions between floral appearance and the visual systems of pollinators
To predict flower colour appearance to another animal requires us to measure the spectral reflectance of different flower parts, quantifying the proportion of light reflected by the flower at different wavelengths – including the ultraviolet
In addition to the reflectance spectra for all the samples we have reviewed, information is available in the database about their colours as perceived by a bee, including photoreceptor excitations and loci in the colour hexagon, the colour triangle and COC space. Where flowers contain parts with different colours, where possible all the flower parts have been measured and included – this is particularly relevant in light of multiple studies
The measurements in the database have been collected over the last 20 years from various sites around the world
The database currently contains hundreds of spectral reflectance records from numerous countries, including Germany, Norway and Brazil. Where possible, the spectral reflectance functions provided are an average calculated from several identical flower parts, from multiple plants of the same species in that location, rather than simply based on a single sample.
The Floral Reflectance Database is a MySQL (Structured Query Language – a method of coding and organising database information) database with a user interface written in PHP (Personal Home Page – a scripting language for websites). This is designed to make it easily accessible via the internet and permit users to search for samples according to specific criteria. The online release of the database functions in all major browsers and is compatible with Windows, Linux and Mac operating systems; however, users of some less common browsers may experience problems with the HexSearch (
The MySQL database consists of 16 tables, dealing with information on the flower sample and characteristics, location, citation information, colour, collection and taxonomy information, and the wavelength measurements themselves (
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Individual boxes indicate discrete data tables and the fields within each one. Lines linking boxes show data tables that are linked by identification codes (ID numbers); the linked fields are indicated by * in the originating table, mapping to fields that are underlined in subsidiary tables. Superscript “1” indicates those records which correspond to the mandatory DarwinCore standard fields.
The format of information contained on each flower sample in addition to the reflectance spectra is also summarised in
Field | Data type | Example |
Family | varchar | Fabaceae |
Genus | varchar | Trifolium |
Species | varchar | repens |
Authority | varchar | L. |
ScientificName | varchar | |
Collector | varchar | Chittka |
Bee colour | varchar | blue-green |
Human colour | varchar | white |
Main flower colour | varchar | Y |
Flower section | varchar | radially symmetric, whole flower upper side |
Country | varchar | Norway |
Town/Area | varchar | Oppdal |
GPS_East | float | [longitude coordinate, where available] |
GPS_South | float | [latitude coordinate, where available] |
Pollinator | varchar | bumblebees, large bees |
Altitude | float | 900 |
Height | float | 15 |
Tube length | float | 3 |
Corolla diameter | float | 15 |
Publication | varchar | Chittka, L. 1996 J. Theor. Biol. 181:179–196 |
Herbarium accession | varchar | [herbarium accession details, where available] |
As previously mentioned, the database often contains multiple reflectance spectra for the same species. Different records may reflect different flower parts being sampled – e.g. the nectar guide versus the keel of the flower – in which case the part measured is specified in the “flowerpart” field. Alternatively, there may be records for different subspecies, cultivars or morphs; many species of plant have more than one floral colour morph
The database web portal consists of several user-friendly features to facilitate access to the data and provide users with additional tools for analysis and consideration of flower colours. These include:
Search facilities
Colour space displays
Reflectance graphs
Raw reflectance data downloads
HexSearch facility, to search for flowers with similar colour hexagon loci.
Visitors to the Floral Reflectance Database are able to use the search facilities to run basic or guided searches for flowers with specific characteristics, e.g. flowers from a particular location, of a particular species or colour, or a combination of these. The Advanced Search (
This page on the FReD website allows the user to choose from many different search options in order to look for specific entries within the database, e.g. reflectance spectra for flowers from a particular genus or collected in a particular country. Most data fields are provided as drop-down menus for ease of use (here, the user is selecting “blue” from the bee colour menu); users can search for keywords or other free text using the basic search bar provided at the top of each page.
Both types of search produce a table of results (
(The query is “blue”, looking for flowers that are either human- or bee-blue). At the top of the page of search results (a), the user has the option to display the colour hexagon (shown) and some basic descriptive statistics about the composition of the results returned. This is hidden by default to reduce page-loading times. The user can then click on an individual species record to bring up more detailed information (b) about that plant species and its floral reflectance graph, as well as viewing the colour locus for that species in three different bee colour space models.
A user will then be able to view the reflectance spectra for all the search results. The use of AJAX (Asynchronous JavaScript And XML) technology keeps loading times as fast as possible by minimising the amount of unnecessary information displayed – a user is presented initially with abbreviated records, and can bring up a flower's full record in a pop-up window by clicking on an individual result (
From the pop-up window for each flower record, there is a button to display the full reflectance data for the sample as a simple table of numeric values. From the page containing the table, it is possible to either return to the flower record, download the reflectance data in comma-separated values (.csv) format, or close the window and return to the table of search results.
The database also has the function to display the loci of each flower on a colour hexagon diagram, a colour triangle diagram and in COC colour space. These are three different models of bee colour space
The colour space coordinates are calculated taking into account the illuminating light (here, normfunction D65
The flower records present the colour space coordinates for each sample on schematic diagrams, but also give the corresponding coordinates for each space numerically. Additionally, the excitation values for the three bee photoreceptor types are provided for users who may find these values useful. The colour space diagrams for each record are provided as Portable Network Graphics (PNG) image files that can be displayed by most modern imaging software, and can be downloaded by users if desired.
Spectral reflectance functions for each record are displayed as a graph in the flower record, for users to assess what pattern of reflectance a flower possess, where the major reflectance peaks occur, etc. These are generated dynamically using the measurements in the Wavelength table, and displayed as a PNG file, so they can be displayed separately from the search results, and saved to a user's local hard drive if required.
The HexSearch (Colour
The user can select up to ten points from the right-hand list, clicking to place each point at the desired location on the colour hexagon. There is an option at the bottom of the page to choose the radius of the search area for each point. When the user then selects “search now”, a page of results will be returned containing all the flower records with colour hexagon loci located within any of the search areas specified. Here, the user has selected to search two areas, each of radius 0.5 hexagon units, one area containing flowers that appear blue to bees (point 1) and one area containing flowers that appear UV-blue to bees (point 2). Therefore, the results will consist of bee-blue and UV-blue flower records only, and only those within the areas selected.
The user can select up to 10 loci of interest on the colour hexagon, which are searched simultaneously, and can specify their position on the hexagon by clicking in the relevant place on the map provided. The user then selects the radius of the search area (in colour hexagon units (hu)), and the function returns a page of results, comprising the flowers with colour hexagon coordinates within the area specified. Hex searches can either be general (e.g. specifying a 0.5 hu radius) or more specific (e.g. 0.05 hu). The centre point of the search can be moved as many times as required.
The database was designed to be used by researchers, and thus we are aware that users may wish to download spectral reflectance curves for their own use. This option is available by selecting the option to “view raw data” and then “view CSV file”. They can then download the reflectance measurements for each species as a.csv (comma-separated values) file, which can be imported into spreadsheets or into other databases.
In order to facilitate potential future inclusion of FReD in a larger meta-database, we have organised the database with structure in line with the international DarwinCore standard. FReD is also linked from the website of the Royal Botanic Gardens, Kew, under their lists of data and publications, in order to widen its audience to researchers who may find it useful.
In the interests of interconnectivity with other databases, all the search results returned by FReD contain links to search results for the same species in the electronic Plant Information Centre (ePIC), the large plant database run by RBG Kew, and the Global Biodiversity Information Facility (GBIF). This immediately widens the information available to users of FReD about species in the database.
We expect the Floral Reflectance Database to be a valuable tool to researchers wishing to make between-habitat or global comparisons of floral colour; application of spectral reflectance data in studies of plant communities has already been demonstrated in multiple studies (examples:
By providing full reflectance spectra of all the samples, we are making available information which makes no
As an example of how the Floral Reflectance Database can be used,
The graph shows the relative percentages of plant species with flowers of different bee colours in four different locations: Ribeirão Preto, Brazil; São Paulo, Brazil; Strausberg, Germany and the Dovrefjell mountains, Norway
In the longer term, we intend to add more spectral reflectance readings in order to facilitate more such comparisons, and in greater detail, including data from South Africa and Costa Rica. We eventually hope to accept reflectance data from other users of the database provided that the measurements are of high quality and include the most important associated information about the sample being measured (i.e. at least species, flower section being sampled, relevant publications, location in which sample was collected). The database also has the potential to be extended to contain additional data fields of interest to pollination studies, such as details of flowering phenology.
We anticipate that as the database grows to encompass more species from diverse international locations, it will become an even more useful resource for many areas of research requiring an objective consideration of flower colours.
We would like to thank E. Hellen and C. Ingram for their work on the prior stages of programming and database development, M. Giurfa for helpful discussion, and the comments of two anonymous referees. The database is hosted by the Positive Internet Company.