Geometry-driven jets underlie dispersal of plants and fungi by raindrops

TL;DR

This study explores how raindrop impacts on specialized concave structures in plants and fungi generate jets that facilitate dispersal, combining experimental observations with a geometric model.

Contribution

It introduces a minimal kinematic model explaining jet formation from droplet impacts on conical surfaces, aligning with natural splash-cup geometries.

Findings

Impact can produce two types of jets crucial for dispersal

Model predicts optimal cone angles for jet formation

Natural splash-cup geometries match model predictions

Abstract

The impact of droplets on concave surfaces is poorly understood, although it is relevant to a mode of dispersal that has evolved independently in several species of plants and fungi. This mode relies on splash-cups, specialized organs that use raindrops to disperse reproductive units away from the parent organism. We investigated the impact of droplets on conical cavities that mimic splash-cups and we found that such impact may lead to the formation of two types of jets, which appear essential for dispersal in nature. We built a minimal kinematic model that explains jet formation, involving the motion of fluid particles along geodesics (shortest paths) on the cone surface and we predicted cone angles that optimize jet formation, consistent with the geometries of natural splash-cups