Do you know why plants in the tropics have big leaves?

If you have ever been to exotic countries - or at least love programs about them, then you could easily notice the following. The size of the leaves increases as you move from the harsh northern climatic zones to tropical latitudes, where humidity and heat reign.

Their area can be different: from 1 mm² to 1 m², or even more. Large-leaved plants, such as bananas, live in the tropics, while small-leaved plants, such as heather and clover, are found closer to cold latitudes.

The relationship between the size of the leaves and their location is obvious. Look at the coconut palm yourself and compare it with the same spruceand doubts will disappear by themselves.

For the first time, botanists drew attention to this trend back in the 19th century, but for a long time they could not find a convincing explanation for this phenomenon.

One theory saidthat large leaves help the plant avoid overheating. Indeed, due to their area, they can accumulate and effectively distribute heat, preventing its concentration in one place. But at the same time, the leaf will capture more sunlight. So, it would seem that large-leaved plants should have developed in cold regions, and not in the tropics.

To unravel this mystery, scientists from Macquarie University in Sydney, led by Ian Wright explored 7,670 plant species living in different latitudes. They looked for a relationship between leaf size and various aspects of climate, such as daytime and nighttime temperatures, rainfall, and humidity.

As a result, Wright's team found that it was just as important for plants to avoid nighttime frosts as they were to avoid daytime heatstroke.

Scientists have found that there is a balance between leaf size and its ability to regulate temperature. It depends on two main factors. First, the plant needs to have enough water in its foliage to cool itself through a process called transpiration - its mechanics are similar to sweating in people.

Secondly, the thickness of the boundary layer of air around the leaves is important. This is a thin area that surrounds each of them. Its dimensions affect the rate of exchange of gases and energy between the sheet and the environment.

Larger leaves have thicker boundary layers of air above them and this makes them more susceptible to extreme temperatures. After all, the thicker this area, the slower transpiration process. The air forms a kind of insulation that makes it difficult to extract heat from the environment at night.

That is why large-leaved plants are not particularly common both in northern latitudes and in desert climates. Thick boundary layers make it difficult to stay warm at night and increase the risk of frost damage. Similarly, in a hot desert climate, the leaf overheats during the day, and there is not enough water for cooling by transpiration.

But in the hot and at the same time humid tropics, large leaves perfect. During the day, they are able to cool themselves effectively by transpiration, unlike desert plants, which cannot afford to lose that much water. And at night they are not threatened by frost damage, which occurs both in northern latitudes and in deserts.

Large leaves can collect more carbon dioxide from the environment, which is essential for photosynthesis. They also allow plants to get more light in dense rainforest where the rays only penetrate through dense canopy. In the tropics there is a lot of moisture, plants do not need worry about the lack of fluid and they may have large leaves for more intensive transpiration.

Finally, in the jungle account for fight for light, water and nutrients. Large leaves help take up more space and overlap neighbors. This means collecting more rainwater and light.

In general, large leaves are good. Of course, even a modest birch would like to have the same panicles as those of palm trees type of royal raffia - 16 meters long and 3 wide. But such hulks will simply freeze at night, and therefore the plants of the middle lane have to be content with what they have.