ULTRASTRUCTURAL BASIS AND FUNCTION OF IRIDESCENT BLUE COLOR OF FRUITS IN ELAEOCARPUS

IRIDESCENT colour, caused by physical effects (thin-film interference, diffraction and Tyndall scattering), is relatively common in animals but exceedingly rare among plants 1. Some benthic marine algae produce blue to violet iridescence 2,3, and the upper leaf surfaces of a few vascular plants from the shady environments of humid tropical forests are iridescent blue 4-6. Blue fruit colour has been assumed to be caused by anthocyanis 7. A survey of such fruits (26 species in 18 genera) in Costa Rica, India, Florida and Malaysia, showed this to be the case, except for the iridescent colour in fruits of Elaeocarpus angustifolius Blume (Elaeocarpaceae). There I show that the colour is caused by a remarkable structure in the epidermis, and provide evidence for its selective advantage.