Iridescent flowers? Contribution of surface structures to optical signaling.
The color of natural objects depends on how they are structured and pigmented. In flowers, both the surface structure of the petals and the pigments they contain determine coloration. The aim of the present study was to assess the contribution of structural coloration, including iridescence, to overall floral coloration. We studied the reflection characteristics of flower petals of various plant species with an imaging scatterometer, which allows direct visualization of the angle dependence of the reflected light in the hemisphere above the petal. To separate the light reflected by the flower surface from the light backscattered by the components inside (e.g. the vacuoles), we also investigated surface casts. A survey among angiosperms revealed three different types of floral surface structure, each with distinct reflections. Petals with a smooth and very flat surface had mirror-like reflections and petal surfaces with cones yielded diffuse reflections. Petals with striations yielded diffraction patterns when single cells were illuminated. The iridescent signal, however, vanished when illumination similar to that found in natural conditions was applied. Pigmentary rather than structural coloration determines the optical appearance of flowers. Therefore, the hypothesized signaling by flowers with striated surfaces to attract potential pollinators presently seems untenable.
Computational Physics, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, NL-9747 AG, Groningen, the Netherlands.|Plant Physiology, Centre for Ecological and Evolutionary Studies, University of Groningen, Nijenborgh 7, NL-9747 AG, Groningen, the Netherlands.
Casper J
CJ
van der Kooi
Computational Physics, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, NL-9747 AG, Groningen, the Netherlands.
Bodo D
http://orcid.org/0000-0002-2727-7128
BD
Wilts
Computational Physics, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, NL-9747 AG, Groningen, the Netherlands.
Hein L
HL
Leertouwer
Plant Physiology, Centre for Ecological and Evolutionary Studies, University of Groningen, Nijenborgh 7, NL-9747 AG, Groningen, the Netherlands.
Marten
M
Staal
Plant Physiology, Centre for Ecological and Evolutionary Studies, University of Groningen, Nijenborgh 7, NL-9747 AG, Groningen, the Netherlands.
J Theo M
JTM
Elzenga
Computational Physics, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, NL-9747 AG, Groningen, the Netherlands.
Doekele G
DG
Stavenga
D035264:Flowers / Q000033:anatomy & histology* / Q000502:physiology* / Q000648:ultrastructure; D031584:Hibiscus / Q000033:anatomy & histology / Q000502:physiology; D031168:Matricaria / Q000033:anatomy & histology / Q000502:physiology; D008855:Microscopy, Electron, Scanning; D010858:Pigmentation; D054817:Pollination; D015398:Signal Transduction; D013499:Surface Properties
coloration; petal striations; plant-pollinator signaling; reflection; scatterometry