Plants That Close Their Leaves at Night – Nyctinasty Explained

Have you ever noticed how some plants close their leaves or flowers when the sun goes down? This phenomenon is called nyctinasty – the nastic movement of leaves in response to the daily cycle of light and darkness In this article, we’ll explore why plants exhibit nyctinasty and which species tend to close up their leaves at night

What is Nyctinasty?

Nyctinasty refers to the rhythmic opening and closing of plant leaves or flowers over a 24-hour cycle. It is controlled by the plant’s internal circadian clock, which regulates various behaviors and physiological processes according to day/night cycles. The opening of leaves and flowers during the day allows plants to carry out photosynthesis, while closing them at night protects their reproductive organs and conserves resources

Nyctinastic movements are driven by special motor cells called pulvini located at the base of plant leaves and leaflets. As pulvini cells lose or gain turgor pressure, they cause the leaves to rise, sink, fold or bend. These movements are triggered by environmental cues like light, temperature and humidity, but they persist even when plants are kept in constant darkness.

Why Do Plants Exhibit Nyctinasty?

Scientists have proposed several evolutionary benefits for nyctinastic leaf movements:

• Water conservation – Closing leaves at night reduces surface area for transpiration, preventing water loss.

• Temperature regulation – Tightly folded leaves retain heat better on cold nights.

• Protection from frost – Closed leaves avoid radiation frost damage.

• Predator avoidance – Closed flowers protect pollen from nocturnal pollinators.

• Energy saving – Closing leaves reduces respiration at night when photosynthesis has stopped.

So in essence, nyctinasty improves the plant’s chances of survival by optimizing their daily energy expenditure and minimizing environmental stresses in the dark.

Examples of Nyctinastic Plants

Many plant species exhibit nyctinastic movements, especially:

• Legumes – Beans, peas, soybeans, clovers
• Oxalis – Woodsorrels, false shamrocks
• Marantaceae – Prayer plants like Calathea, Maranta
• Faboideae – Mimosa pudica, Albizia julibrissin
• Brassicaceae – Arabidopsis thaliana
• Malvaceae – Cotton, hibiscus, rose mallow

Among non-flowering plants, some ferns (Adiantum genus) and cycads also show nighttime leaf closure.

For ornamental plants, tulips, crocuses, poppies, morning glories and lotuses display spectacular nyctinastic movements that contribute to their visual appeal. Even the leaves of Acacia and Oxalis houseplants can be observed folding in the evenings.

The Mechanism Behind Nyctinastic Movements

The opening and closing of nyctinastic plant leaves is regulated by a pigment called phytochrome. This photoreceptor senses the presence or absence of red light and triggers downstream responses.

During the day, the Pfr form of phytochrome accumulates in plant tissues under red light. This activates the proton pumps in pulvini cells, making them turgid, so the leaves open up.

At dusk, the lack of red light causes phytochrome to convert to its Pr dark form. This suppresses proton pump activity, depleting turgor pressure in pulvini cells and causing leaves to droop and close.

Phytochrome-regulated ion fluxes and turgor changes initiate nyctinastic movements, while the plant’s endogenous circadian clock sustains the rhythms even in the absence of environmental cues.

Benefits of Observing Nyctinastic Plants

For plant hobbyists and gardeners, nyctinastic plants lend a lot of visual interest through their dancing leaves and flowers. You can take advantage of the phenomenon for various purposes:

• Add architectural flair to the garden by planting oxalis, ferns, lotuses etc.

• Grow prayer plants indoors to enjoy their geometric folding patterns.

• Conduct biology experiments by manipulating photoperiods for nyctinastic plants.

• Demonstrate circadian rhythms by recording cyclical movements.

• Investigate phytochromes by exposing plants to different light colors.

So if you notice the leaves of your gardenia, begonia or beans mysteriously closing up as the sun sets, marvel at this intriguing example of plant movement governed by the circadian clock! The nyctinastic plants are revealing their daily sleep-wake cycles just like us diurnal humans.