Implications of reflectance and fluorescence of Rhododendron indicum flowers in biosignaling.

A quantitative evaluation of the light emerging from intact petals of Rhododendron indicum flowers of different colours was performed. Reflectance and fluorescence emission were analyzed in detail. The fluorescence quantum yield of petals was determined on entire flowers. The obtained values varied from 7.6 x 10(-5) to 6.3 x 10(-4) for the emission in the blue region of the electromagnetic spectrum and from 2.4 x 10(-5) to 1.9 x 10(-4) for the emission in the red one. The fluorescence emission that resulted was negligible compared to the light reflected by the petals, so it was concluded that in this case only reflectance signals should be relevant in biosignal communication with pollinators. In addition, a quantitative estimation of the relative amount of photons absorbed by eye photoreceptors was achieved. Quantum catches were calculated for humans, for honeybees and for a species of bird. Contrasts to background values were also estimated in relation to the ability to detect flowers.