Raindrop impact location predicts seed dispersal distances in rain-activated splash cup plants

Splash cup plants exhibit rain-activated seed dispersal in which raindrops impact millimeter-sized cup-shaped fruiting bodies. The resulting splash can carry seeds up to a meter away from the plant. Previous research has examined this dispersal mechanism in vivo as well as with 3D-printed model cups. Previous work determined the optimal cone shape for the cups and showed that raindrop impacts that hit off-center led to longer dispersal distances than on-center. However, the effect of impact location was not systematically studied. Here, we build upon this work by systematically studying how raindrop impact location affects seed dispersal distances. We performed experiments across a range of 3D-printed biomimetic conical cup shapes and hydrophobic glass beads that mimic seeds. Our results show that the impact location of the incoming raindrop is a significant predictor of seed dispersal distances. We find that seed dispersal distance varies with impact location, cone shape, and the number of seeds in the cup. These results suggest that raindrop impact location must be accounted for when measuring dispersal, and that even small (< 0.5mm) departures in impact location have significant effects on the dispersal distances of seeds.