  The spirally arranged stems of the spikemoss Selaginella lepidophylla, an
ancient resurrection plant, compactly curl into a nest-ball shape upon
dehydration. Due to its spiral phyllotaxy, older outer stems on the plant
interlace and envelope the younger inner stems forming the plant centre. Stem
curling is a morphological mechanism that limits photoinhibitory and thermal
damages the plant might experience in arid environments. Here, we investigate
the distinct conformational changes of outer and inner stems of S. lepidophylla
triggered by dehydration. Outer stems bend into circular rings in a relatively
short period of desiccation, whereas inner stems curl slowly into spirals due
to hydro-actuated strain gradient along their length. This arrangement eases
both the tight packing of the plant during desiccation and its fast opening
upon rehydration. The insights gained from this work shed light on the
hydro-responsive movements in plants and might contribute to the development of
deployable structures with remarkable shape transformations in response to
environmental stimuli.
