Splash-cups and rain dispersal of Marchantia polymorpha gemmae

In many plant species seedlings are dispersed in nature by the way of wind or animals. This in not the case for Marchantia polymorpha whose gemmae are ejected from a splash-cup organ by the fall of raindrops. This splash-cup is a small conical cavity of a few milimeters that contains the plants gemmea. When a raindrop falls on this cup in a non centered way there is formation of a jet that carries a few gemmea with it. This dispertion mechanism if very efficient as a single drop can eject gemmea up to a meter away from the plant.

Our purpose is to study this dispersal mechanism by using a biomimetic approach. 3D-printed targets of  3mm diameter are impacted by drops of the same size travelling at 4m/s. We aim to understand the influence of the plant splash-cup geometry, especially the cone angle and the presence of decorations on its border, on the efficiency of this process. To this end we printed various shapes, ranging from the flat pillar to the high angle cone, each having or not border decorations. Drop impacts on the target are recorded with two high speed cameras at 10.000 fps from the side and from above. With these data we will devellop a simple model to explain the mechanism of jet formation depending on drop centering and on the geometrical parameters of the target.