The alternation of day and night makes the flowers open or close their petals. These periodic movements are known to botanists as nictinastias.
Most plants close their flowers to protect their delicate sexual structures from the harsh conditions that appear when the sun goes down. Thus, for example, the night-time dew can moisten pollen grains, causing them to germinate before pollination. Generally, the floral opening and closing movements are caused by variations in ambient temperature (thermonastia) and the intensity of light (photonastia).
However, in coastal and desert areas there are so-called night-flowering plants, such as Melandrium album and Silene nutans , which open at dusk.
