Many plants display sleep movements (known as nyctinasty), folding their leaves closed at night, thought by some to be a defense against nocturnal herbivory.
This can be seen in French Bean, Wood Sorrel, Clover, Sensitive Plant (Mimosa pudica) and in the Persian Silk Tree here and in the Brookside bike park nearby. Such movements of leaves are caused by changes in turgor pressure – the swelling of plant cells with water – at the base of the stalks of the leaves of these species. The opening movement requires an increase of turgor in the top part of the leaf stalk, and the closing movement requires an increase of turgor in the bottom part. These movements have been shown to be under control of the circadian clock.
An understanding of the complex cellular physiological mechanisms resulting in these turgor movements was obtained using this species. Look out for its pink, fluffy-headed flowers in the summer.