Why do the leaves of the sycamore look like little palms?

Author: Hao Yun

Reviewer: Wang Kang, Director of the Science Museum of the North Garden of the National Botanical Garden

There is an article in the primary school Chinese textbook called "The Cement Road Covered with Golden Palms". It talks about the yellow leaves of the plane trees falling to the ground after the autumn rain, and "each fallen leaf of the plane tree is like a small golden palm."

The "French plane tree" that people often refer to is the Platanus × acerifolia, but in fact it is neither from France nor a plane tree. It is just because the first plane tree to be introduced and planted in China was in the French Concession in Shanghai, people mistakenly call it the "French plane tree". And because it was first popular in London, England to plant it as a street tree, it also has a common name, the English plane tree, which is called the London plane in English.

The common name "Platanus" actually corresponds to the plane tree, whose scientific name is Platanus orientalis.

As the name suggests, it is related to the Plane Tree. The academic community believes that it is a hybrid between the Plane Tree and the Plane Tree that gave rise to the Plane Tree. The multiplication sign "×" in the name of the Plane Tree indicates that it is a hybrid. Plane trees are very suitable as street trees. They are tall, lush, and have large leaves, which are very suitable for summer shade. Therefore, they are widely planted around the world and are more common than the real plane tree (Firmiana simplex).

Among them, the hybrid sycamore is more cold-resistant and adaptable than its parent, so it is planted more frequently. Over time, not only do people forget that the sycamore is not a true sycamore, they even forget that the sycamore is a French sycamore. The "French sycamore" that appears in elementary school textbooks is probably an "impostor" sycamore.

However, whether it is the "fake French plane tree" two-ball plane tree or the "real French plane tree" three-ball plane tree, their leaves do look like palms. Why do leaves look like human palms?

This is of course due to our association. Strictly speaking, it is not the leaves that look like palms, but the palms that look like leaves. After all, leaves of this shape have existed in nature for a long time, but it is our human palms that appeared relatively late.

Then, why do leaves grow in petals like this?

Palmate fissures in leaves are not uncommon. In addition to the real and fake "Paracel", many leaves have "petals". However, such leaves are almost always very large, with a sharp tip at the end of each "petal", and thick veins leading all the way to the tip of the leaf.

Therefore, some scientists speculate that this palm-like shape makes it easier for plants to transport nutrients.

The leaves of plants consume a lot of water all the time. Chloroplasts use water and carbon dioxide to produce a lot of nutrients through photosynthesis. Where does this water come from? The roots of plants can absorb water and transport it to the leaves through vascular bundles, and in turn transport the nutrients produced by photosynthesis back to the stems and roots. The transport channels in the leaves are leaf veins.

If there is an area of ​​the leaf that is too far from the veins, the transport efficiency will be lower. If the leaf is small, it doesn't matter. But for leaves as big as the "Plantain Tree", it is necessary to improve the transport efficiency. A good way to improve efficiency is to make the leaf as close to the thick veins as possible. As a result, the leaf grows close to the veins and looks like a palm.

This is palmate veining, which refers to the distribution of three or more veins of almost equal thickness starting from the base of the leaf, with no master-slave relationship, which is different from the more common reticular veins (such as camphor leaves) and parallel veins (such as ginkgo leaves). The shape of the leaves matches the distribution of the veins, probably to facilitate the transport of nutrients.

Have you ever thought about the distribution of leaf veins in different plants? Pay close attention to the leaves falling in the autumn wind, and you may be surprised.