Nyctinasty in Ranunculus Flowers

May 21, 2020

Photographer: Menashe Davidson
Summary Author: Menashe Davidson

One of the many things I enjoy about my apartment garden, in Rishon LeZiyyon, Israel, is following the development of the various plants and flowers. While strolling among the flowers on April 3, 2020, just after sunset, I noticed that the Ranunculus (buttercup) flowers tend to retire after the Sun goes down. Flower petals close in stems bend down, preparing to sleep for the night. (bottom photo). But several hours after the next morning’s sunrise, the flower stems are erect again, and the flowers are open, exposing their reproductive organs. (top photo -- taken near midday)

This phenomenon is called nyctinasty, a type of plant movement that’s related to night and day, directed by the plant’s diurnal cycle. The reproductive organs of ranunculus flowers have evolved to achieve a successful reproduction strategy. The flower doesn’t open when it’s wet and heavy with dew, rather, it waits until the pollen is dry so that it can be more easily transferred by pollinators.