title: Functional optics of glossy buttercup flowers.
abstract: Buttercup (Ranunculusspp.) flowers are exceptional because they feature a distinct gloss (mirror-like reflection) in addition to their matte-yellow coloration. We investigated the optical properties of yellow petals of severalRanunculusand related species using (micro)spectrophotometry and anatomical methods. The contribution of different petal structures to the overall visual signal was quantified using a recently developed optical model. We show that the coloration of glossy buttercup flowers is due to a rare combination of structural and pigmentary coloration. A very flat, pigment-filled upper epidermis acts as a thin-film reflector yielding the gloss, and additionally serves as a filter for light backscattered by the strongly scattering starch and mesophyll layers, which yields the matte-yellow colour. We discuss the evolution of the gloss and its two likely functions: it provides a strong visual signal to insect pollinators and increases the reflection of sunlight to the centre of the flower in order to heat the reproductive organs.
authors.affiliation: Computational Physics, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands casper.vanderkooi@unil.ch.|Department of Ecology and Evolution, University of Lausanne, Le Biophore, 1015 Lausanne, Switzerland.
authors.forename: Casper J
authors.identifier: 0000-0003-0613-7633
authors.initials: CJ
authors.lastname: van der Kooi
authors.affiliation: Plant Ecophysiology, Groningen Institute for Evolutionary Life Sciences, University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands.
authors.forename: J Theo M
authors.initials: JT
authors.lastname: Elzenga
authors.affiliation: CBS-KNAW Fungal Biodiversity Centre, Uppsalalaan 8, 3508 AD Utrecht, The Netherlands.
authors.forename: Jan
authors.initials: J
authors.lastname: Dijksterhuis
authors.affiliation: Computational Physics, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands d.g.stavenga@rug.nl.
authors.forename: Doekele G
authors.identifier: 0000-0002-2518-6177
authors.initials: DG
authors.lastname: Stavenga
mesh_terms: D035264:Flowers / Q000737:chemistry* / Q000166:cytology / Q000378:metabolism; D008962:Models, Theoretical; D055095:Optics and Photonics / Q000379:methods; D010858:Pigmentation; D019441:Plant Epidermis / Q000737:chemistry* / Q000166:cytology / Q000378:metabolism; D031947:Ranunculus / Q000737:chemistry* / Q000166:cytology / Q000378:metabolism
keywords: epidermis; flower colour; pigment; starch; structural coloration; thin-film interference