  Appendages of seeds, fruits and other diaspores (dispersal units) are
essential for their wind dispersal, as they act as wings and enable them to
fly. Whirling fruits generate an auto-gyrating motion from their sepals, a leaf
like structure, which curve upwards and outwards, creating a lift force that
counteracts gravitational force. The link of the fruit's sepal shape to flight
performance, however, is as yet unknown. We develop a theoretical model and
perform experiments for double-winged bio-mimetic 3D-printed fruits, where we
assume that the plant has a limited amount of energy that it can convert into a
mass to build sepals and, additionally, allow them to curve. Both hydrodynamic
theory and experiments involving synthetic, double-winged fruits show that to
produce a maximal flight time there is an optimal fold angle for the desiccated
sepals. A similar sepal fold angle is found for a wide range of whirling fruits
collected in the wild, highlighting that wing curvature can aid as an efficient
mechanism for wind dispersal of seeds and may improve the fitness of their
producers in the context of an ecological strategy.
