Structural and mechanical properties of humidity-responsive Geraniaceae awns

Hygroscopic deformations in plants are passive movements within specialized structures triggered by changes in environmental humidity. In the Geraniaceae, the sterile extension of the mericarp, called awn, facilitates seed dispersal by actuating hygroscopic coiling. Notably, the morphological characteristics and regional distribution of awns vary significantly among the family species, suggesting different mechanisms at the base of dispersion. Despite these variations, no prior investigation has solely focused on examining the combination of the structural and mechanical properties of the awn. Thus, this study fills the gap by conducting an in-depth comparative analysis of the awns from two Geraniaceae species, Pelargonium appendiculatum (L.f.) Willd. and Erodium gruinum (L.) L'Her., which exhibit similar coiling behavior but possess distinct structural features. Through an interdisciplinary approach, we have identified key internal structural characteristics that profoundly impact the awn's mechanical properties and hygroscopic response, directly influencing its movement. Our comprehensive findings highlight distinct dispersion mechanisms tailored to each species, providing new insights into the functional role of awn structures. This study not only advances our understanding of plant biomechanics but also highlights the intricate relationship between structure and function.