The enchanting daily dance of flowers tracking the sun

This phenomenon is known as heliotropism, from the Greek for ‘sun turn’, and while it’s an effect that’s been observed for millennia, it’s only recently that it’s been fully understood by science.

Gardeners will recognise the tendency of growing plants to turn towards a strong light source. Most species will slowly twist their stems to let as much sunlight as possible fall onto their leaves. This movement during growth is known as phototropism, and it happens far too gradually to perceive in real-time.

Aside from this common growth behaviour, some plants take their sun-seeking activities to an entirely new and speedier level. With an effect most famously seen in sunflowers (hence the name), these plants closely track the position of the sun across the sky over the course of the day, rather than just adjusting their growth in the general direction of the brightest light. A sun-loving plant like this will start the day facing east to catch the earliest rays, and over the daylight hours, it’ll rotate toward the west to follow the sun down in the evening. Sometimes move through an arc of almost 180⁰. This spectacle is known as heliotropism.

This behavior allows the plants to maximize their exposure to sunlight, which is essential for photosynthesis, the process by which plants convert light energy into chemical energy to fuel their growth. In Australia, many sun-loving plants exhibit heliotropism as a survival strategy to cope with the intense sunlight and high temperatures often found in this region. By tracking the sun’s movement throughout the day, these plants can regulate their temperature and optimize the absorption of sunlight.

There are two main types of heliotropism observed in plants: solar tracking and nyctinasty. Solar tracking involves the movement of plant parts, such as leaves or flowers, in response to the sun’s position. This movement can be observed as the plant adjusts the orientation of its leaves to face the sun during the day. On the other hand, Nyctinasty refers to the rhythmic opening and closing of flowers or leaves in response to the daily light-dark cycle.

Heliotropism is particularly important for plants in arid or semi-arid environments, such as many regions in Australia, where water availability is limited. By tracking the sun, these plants can reduce water loss through transpiration. By angling their leaves or flowers to minimize direct sunlight exposure during the hottest parts of the day, they can prevent excessive evaporation from their surfaces.

In addition to optimizing sunlight exposure and reducing water loss, heliotropism can also benefit plants by improving the efficiency of photosynthesis. By directing their leaves towards the sun, plants can capture more sunlight, maximizing the amount of energy they can produce.

However, recent research has found another explanation for solar tracking that’s just as important to the long-term success of a plant species. Heliotropism is found only in younger, fast-growing plants. As they reach maturity, the stems toughen up and the flowers become fixed mostly facing east, catching direct sun only in the mornings. Why would this happen, when a greater overall level of sunlight would be captured by facing broadly to the north, like most other sun-seeking plants? The answer is that by catching the first rays as the sun rises, the flower warms up more quickly at the start of the day. It puts out a stronger perfume before its nearby competitors, and so attracts more early-riser bees and other insects to do their essential pollinating work.

Overall, heliotropism in sun-loving plants in Australia allows them to adapt to challenging environmental conditions by maximizing light absorption, reducing water loss, and enhancing photosynthetic efficiency. A remarkable strategy helps these plants thrive in their specific habitats. Many other Asteraceae or daisy family members also follow the daily pattern to some extent, including dandelions, poppies, buttercups, and tulips.