Abstract
The flowers of poppies (Papaveraceae) exhibit bright colours, despite their thin and floppy petals. We investigated the optical properties of flowers of Papaver rhoeas, P. dubium, Meconopsis cambrica and Argemone polyanthemos using a combined approach of anatomy, spectrophotometry and optical modelling. The petals of Papaver flowers are composed of only three cell layers, an upper and lower epidermal layer, which are densely filled with pigment, and an unpigmented mesophyll layer. Dense pigmentation together with strong scattering structures, composed of serpentine cell walls and air cavities, cause the striking poppy colours. We discuss how various aspects of the optical signal contribute to the flower’s visibility to pollinators.
Highlights
Flowers have been called sensory billboards, because they feature numerous traits to entice pollinators
The reflectance value of 35% is high when considering their very minimal thickness. With their average thickness of only three cell layers, be such efficient reflectors? The answer comes with the interior structure and shape of their cell walls
Microscopical investigation of individual cells showed that the serpentine-curved epidermal cell walls in combination with surrounding structures strongly scatter the light flux propagating in the petal interior, causing
Summary
Flowers have been called sensory billboards (sensu Raguso 2004), because they feature numerous traits to entice pollinators. The colours of flowers are due to two basic optical principles: (1) reflection and scattering of light by the floral structures, and (2) selective absorption in a specific wavelength range by floral pigments (van der Kooi et al 2016, 2019). P. rhoeas has fairly large and exceedingly thin petals, yet they are deeply coloured and are relatively strong scatterers (van der Kooi et al 2016) These findings raise the question as to the anatomical details of P. rhoeas flowers that cause the extreme optical characteristics, and whether related species share similar properties. Poppies are a group of genera in the subfamily Papaveroideae of the Papaveraceae, which is an early diverging eudicot family They include species of Papaver, Meconopsis, and Eschscholtzia, and comprise many iconic species well-known for their showy flowers. We discuss our results in context of the plant’s ecology and visual ecology of their pollinators
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