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nyctinastythe so-called ‘sleep movements’ of plants in which the leaves regularly droop at night in a form of DIURNAL RHYTHM. The activity is particularly common in plants with compound leaves, such as Oxalis acetosella, the wood sorrel.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005