Reversible bending of U-shaped plant petioles under dehydration

The shape of plants can be sensitive to dehydration. Here, we focus on herbaceous plants whose petiole cross-section is U-shaped and contains a lot of water. Among a large range of plants showing the same behaviour, we examine Spathiphyllum that exhibits a pronounced, sudden but reversible drooping under dehydration. We show that it is the consequence of a high-amplitude hinge mechanism located at the base of its long petioles, similar to a carpenter's tape folding under sufficient load. Mechanical testing demonstrated that small-amplitude bending rigidity decreases by only a factor of three during dehydration, due to tissue shrinkage rather than material softening. The petiole is composed of water-rich parenchyma tissue: drooping occurs abruptly at 35%-40% of mass loss, remaining reversible unless dehydration is prolonged. Inspired by these observations, we introduce a biomimetic hinge which offers a programmable bending stiffness and nonlinear behaviour under load, with applications in computing mechanical metamaterials.