Plants have developed various strategies to ensure their reproduction and territorial expansion. Among these, some rely on the action of raindrops to disperse their reproductive units, known as propagules. It is this fascinating phenomenon that Ana Bratu and her colleagues at LadHyX have studied in detail.
The mechanism involves small "basket-like" structures, found in some plants like the fountain liverwort (Marchantia polymorpha), as well as in fungi and grasses. These structures, though present in evolutionarily distant organisms, demonstrate evolutionary convergence due to their effectiveness.
At the center of these conical baskets are the propagules. When a raindrop hits the basket's wall, the water exits as a unidirectional jet, expelling the propagules and enabling their dispersal. The dynamics of a droplet impacting a concave surface were previously little understood in fluid mechanics.
To study this phenomenon, the team used 3D printing to recreate these structures and conduct controlled experiments, alongside building a kinematic model. They discovered that water, after impact, follows the geodesics of the conical walls, converges at the opposite point, and the collision of water particles generates the jet.
By varying the opening angle of the baskets, researchers observed that the jets can be horizontal (promoting long-distance dispersal) or vertical (helping propagules attach to plants above, particularly in fungi). The angles that optimize the kinetic energy of these jets align with those observed in nature.
Research continues in partnership with the University of La Réunion to explore the influence of the environment on the geometry of these propagule baskets.
