Yes, many varieties of Osteospermum flowers do close at night, a phenomenon known as nyctinasty. This is not a random occurrence but a deeply ingrained, rhythmic behavior driven by the plant's internal circadian clock, much like our own sleep-wake cycle. From the plant's perspective, this daily movement is a highly efficient and adaptive strategy for survival and reproductive success. The closing of the petals is a visible response to the environmental shift from day to night, primarily triggered by changes in light and temperature.
The core reason for this nightly closure is protection. The delicate reproductive organs of the flower—the stamens and pistil—are its most valuable assets. By folding its petals inward, the flower creates a protective barrier against potential nightly threats. These include dew and frost, which could damage sensitive tissues or promote fungal growth if they settled directly on the pollen and stigma. Furthermore, it offers a degree of protection from nocturnal insects that might not be effective pollinators and could potentially damage the flower. This closure also helps the plant conserve valuable resources like scent and nectar, which are unnecessary at night when their primary pollinators are inactive, preventing them from evaporating or being wasted.
The physical process of opening and closing is governed by a small, specialized motor organ at the base of each petal or flower head called a pulvinus. This segment is composed of cells that can rapidly change their internal water pressure. During the day, stimulated by light, cells on the inner side of the pulvinus pump in potassium ions. Water follows by osmosis, causing these cells to become turgid and swell, which forces the flower to open. As light fades and temperatures drop at night, these cells lose their turgor pressure by expelling water and ions. The cells on the opposite side of the pulvinus then become relatively more turgid, causing the entire petal to bend inwards and the flower to close. This elegant mechanism is a purely physiological response.
It is important to note that not every Osteospermum cultivar exhibits this behavior with the same intensity. Through selective breeding, some modern hybrids have been developed that remain open for longer periods or may not close as tightly. The strength of the response is also heavily influenced by environmental conditions. On a cloudy, dim day, the flowers may not open as fully or may begin to close earlier. Conversely, on a particularly cold night, the closure might be much more pronounced. This flexibility demonstrates the behavior's role as an adaptive tool, allowing the plant to fine-tune its activity based on immediate conditions to maximize its chances of pollination during optimal times.
