Physical mechanisms of rehydration in Polypodium polypodioides, a resurrection plant.

Resurrection plants have an amazing ability to withstand water drought. Here we investigate experimentally the rapidity of such revivals using the resurrection fern (Polypodium polypodioides) as a model example. Upon drying, the leaves of the resurrection fern fold into a thin cylindrical shell, thus protecting the photosynthetic area from light. In the dry state the fern looks dead, but will quickly come back once exposed to water by unfolding the cylindrical shell into a nearly planar sheet. We investigate here the mass and radius of curvature of the cylindrical shell as a function of time after rehydration and develop a phenomenological model to describe the observed phenomena. In particular, we demonstrate that the mass of the rehydrating plant follows a simple kinetic relationship, whereas the unfolding is governed by a more complex nonlinear constitutive relationship between the water uptake and the induced strain.