The flowers of some plants close at night and open during the day in response to stimuli such as light and temperature that influence the biochemical processes regulating the opening and closing of the flowers, called nyctinasty and photoperiodicity.
These opening and closing movements of flowers are mainly the result of a phenomenon called nyctinasty. This process relies on variations in internal pressure within the cells located at the base of the petals or leaves, special cells known as motor cells. During the day, these cells absorb water, swell up, and voilà, the flower opens. When night falls, they lose water, deflate, and the flower quietly closes. At its core, this mechanism primarily depends on changes in ion concentration (especially potassium), driven by light signals or the internal clocks of plants. These variations in internal pressure are therefore largely linked to the day/night rhythms sensed by small light-sensitive proteins called phytochromes.
Light acts as a true trigger signal for flowers. Specialized cells in the petals capture light intensity, especially at sunrise and sunset. These cells then transmit the information to plant tissues, triggering opening or closing movements. But it's not just a matter of direct light: even in total darkness, many flowers maintain a precise rhythm thanks to their internal biological clock. This internal clock is somewhat like a metronome set to 24 hours, naturally adjusted according to day and night. This phenomenon, known as the circadian rhythm, allows flowers to always be perfectly timed, open at the right moment to attract the appropriate pollinators.
This behavior helps protect the reproductive organs of plants from moisture and cool night temperatures, thereby reducing the risks of fungal diseases or cold-related damage. By remaining closed at night, flowers also limit unnecessary energy loss, as there are almost no pollinating insects during this time. In contrast, by blooming during the day, they better attract daytime pollinators such as bees or butterflies with their colors and scents that are visible and perceivable only when they are open. This precise rhythm significantly increases their chances of successful pollination and thus their ability to produce seeds and preserve the species.
The Four o'clock flower is a classic: its blooms open at dusk, filling the air with fragrance until the following morning. In contrast, the famous dandelion closes its petals at twilight only to open them again as soon as the sun appears. The sacred lotus also follows this pattern, as its large, majestic flowers close each night to protect their pollen. The humble daisy also adheres to this movement, carefully closing its small flowers at nightfall or before bad weather. As for the Oxalis, or false clover, it gently folds its leaves and petals as soon as the light diminishes, as if it were going to sleep peacefully.
Even though most flowers gently follow the day-night rhythm, some plants are outright rebels. For example, the night-blooming cactus (Selenicereus grandiflorus) prefers to open its blooms only once night falls, offering its fragrant flowers to attract nocturnal pollinators like bats or moths. In contrast, other plants, such as night jasmine (Cestrum nocturnum), wait for complete darkness to open their aromatic flowers. A few plants from cold or mountainous regions go even further: they completely ignore sunlight and adjust their schedules based on criteria like temperature or weather conditions to avoid wasting their energy unnecessarily. In short, nature enjoys keeping us guessing.
Some plants can adjust the opening and closing times of their flowers based on local weather conditions, allowing for better adaptation to their immediate environment and optimizing their chances of survival and reproduction.
Night-blooming flowers such as night jasmine or evening primrose specifically open in the evening, often releasing an intense fragrance at dusk to attract nocturnal pollinators like certain species of butterflies and bats.
The lotus is famous for closing and partially submerging underwater at night, only to re-emerge and open the following day, symbolizing rebirth and spiritual purity in various cultures.
Some flowers, like those of the sunflower, follow the path of the sun throughout the day due to a phenomenon called 'heliotropism'. This orientation allows them to optimize light exposure and effectively attract pollinators.
No, flowering nyctinastic plants exist in various climates and geographical regions all over the world. Examples can be found from tropical regions to temperate zones.
Yes, in some cases, if a plant is subjected to significant environmental stress, such as prolonged drought or drastic changes in light, it may temporarily lose or disrupt its natural rhythm of flower opening and closing.
Yes, the phenomenon is completely reversible and generally repeats itself every day throughout the flowering period. The flowers continue to open each morning and close each evening until they age or are pollinated.
It depends on the plant species. Some nyctinastic flowers attract their pollinators mainly during the day when their blooms are open, while other species, known as nocturnal, specifically attract night insects and exhibit the opposite behavior by opening their flowers primarily at night.
No, although many use similar mechanisms involving light and internal circadian rhythms, there are different physiological and chemical methods depending on the species, particularly based on specific plant hormones or changes in hydraulic pressure within the tissues.
No one has answered this quiz yet, be the first!' :-)
Question 1/5
