Why do daisies close at night?

Many species of plants have flowers with nyctinastic (sleep) movement and nastic movements are all defensive or protective in function. The flower is the reproductive organ of the plant and folding the corolla will shield the pistil, stamen and nectaries from nighttime herbivores and prolong the life of the flower to improve the chances of being fertilized. Some species will even be triggered to close in dark and stormy weather.

The nyctinastic flowers closure is triggered by the loss of daylight but some are so sensitive to light loss the plant will close even in the day if the weather darkens sufficiently. The petals remain closed as long as the clouds &/or the night persists. Other plants close and open at set times and are not sensitive to weather. Plants that respond to weather may be more susceptible to damage by rain. Tulips close with dark skies. The closure may also protect the corolla from the nightly drop in temperature in plants that bloom early or at high altitude.

Researchers once thought petal closure might help the flower prevent drying but Waterlilies also have nyctinastic movement. Since even water plants have nyctinastic movement closure isn’t selected to preserve hydration.

Linnaeus did actually work out a clock based upon flowers to tell time, he used flowers with fixed opening times that are independent of the weather. He called these aequinoctales rather than meteorici because they do not respond to meteorological conditions to regulate opening and closing.

Daisies do a little thing called photosynthesis. This means that it absorbs sunlight to create energy. At night, there is no sun, so the pedals of the daisies close. In the morning, when the sun starts to shine, the pedals open up again to perform photosynthesis.