Platanus

Plane trees are very tall trees.

Their bark peels off in patches. This makes the trunk look scaly.

These trees grow round fruit. The fruit looks like small balls.

Tiny hairs on the fruit help it fly in the wind.

Some plane trees grow near water. Other kinds grow well in big cities. One kind is called the London plane. It is a mix of two different trees.

Small hairs on the tree can be itchy. If the wind blows them, they can bother your eyes. You can wear a mask to stay safe.

Plane trees are amazing to see in a park.

Plane trees are very tall trees.

They belong to a group called Platanus. Most of these trees grow near water. However, some can live in dry soil. One kind is the London plane. This tree is a hybrid. A hybrid is a mix of two different types. The London plane mixes trees from North America and Europe. It grows very well in big cities.

The bark of these trees peels off in patches. This makes the trunk look scaly. The trees also grow round fruit. These fruits look like small balls.

Each ball has many tiny seeds inside. These seeds have small, stiff hairs. The hairs help the wind carry the seeds away.

Sometimes, the trees can get sick. A fungus called anthracnose can make leaves fall off. This happens most in cold, wet spring weather. The trees can usually get better. Also, tiny hairs on the tree can be itchy. If the wind blows these hairs, they can bother your eyes or throat. You can wear a mask to stay safe.

Plane trees are a group of very tall trees. They belong to a genus called Platanus. Most of these trees grow near rivers or in wet areas. However, they can also live in dry soil if they are planted by people. Many people call them sycamores, especially in North America.

These trees are important parts of many different landscapes around the world. They can grow to be quite large and strong.

These trees have a very interesting way of growing. The bark on the trunk peels off in uneven patches. This makes the tree look scaly or mottled.

The trees also produce round fruit that look like small balls. Each ball is between 2.5 and 4 centimeters wide. Inside the ball, there are hundreds of tiny seeds called achenes. Each seed has a small, stiff hair attached to it. These hairs help the wind carry the seeds to new places.

Scientists have studied these trees for a long time. The name Platanus comes from an Ancient Greek word. It originally referred to the Oriental plane tree. Fossil records show that leaves and fruit from these trees existed during the Paleocene period. This was a very long time ago. Today, we know there are different groups of these trees. Some live in North America and others live in Eurasia.

There are many specific types of plane trees. The Oriental plane is a famous one from Eurasia. In North America, you can find the American sycamore.

There is also a special tree called the London plane. This tree is a hybrid, which means it is a mix of two different species. It was made by mixing the American sycamore with the Mediterranean Oriental plane. Because it is a mix, it grows very well in big cities like London. It is a very popular tree to plant in parks.

Plane trees can sometimes face hard jobs like diseases. A fungus called anthracnose can make the leaves fall off during a wet spring. Another problem is a wilt disease called Ceratocystis platani. These trees also have tiny hairs that can sometimes bother people. If the wind blows these hairs during dry weather, they can make eyes or throats feel scratchy. This is sometimes called "platanus cough." You can stay safe by wearing a mask or glasses if the wind is high.

The genus *Platanus* consists of a small number of tree species. These trees are the only living members of the family Platanaceae. Most mature members of this genus are very tall. They are often called plane trees or planes in English. In North America, some species are known as sycamores.

This name is most common for *Platanus occidentalis*. The genus name itself comes from an Ancient Greek word. That word originally referred to the *Platanus orientalis*, or the Oriental plane. These trees are important to many different ecosystems around the world.

Plane trees have a very distinct way of growing and reproducing. They are monoecious, which means male and female flowers grow on the same plant. The flowers are small and grow in round shapes called globose heads. These trees are wind-pollinated. The male flower-heads fall off after they release their pollen. After pollination, the female flowers develop into small units called achenes. These achenes form an aggregate ball that serves as the fruit. The fruit ball is usually 2.5 to 4 centimeters in diameter. It contains several hundred achenes, each with a single seed. Each achene has a tuft of stiff, yellow-green bristles. These bristles act like tiny parachutes to help the wind carry the seeds away.

There are two main subgenera within the *Platanus* genus. The first is subgenus *Castaneophyllum*, which contains only one species: *P. kerrii*. The second is subgenus *Platanus*, which includes almost all other species. The leaves of the trees in subgenus *Platanus* are simple and alternate. They have a palmate outline, which means they are shaped like a hand.

A unique feature is the leaf stalk, or petiole. The base of the petiole is enlarged and wraps around the young stem bud. This protects the bud until the leaf falls off in the autumn. Most species are deciduous, meaning they lose their leaves every year. The only exception is *P. kerrii*.

Scientists have discovered that these trees have a complex evolutionary history. Fossil records of *Platanus* leaves and fruit date back to the Paleocene. Recent studies using gene sequences have identified two major lineages. One is called the ANA clade, or the Atlantic North American lineage. The other is the PNA-E clade, the Pacific North American-European lineage.

These lineages show that the trees have experienced reticulate evolution. This means they have undergone ancient or recent hybridization. Hybridization occurs when two different species breed to create a new type of tree. This process makes their family tree look more like a network than a simple branch.

One of the most famous examples of this is the London plane. This tree is a hybrid known as *Platanus × hispanica*. It was created by crossing the North American *P. occidentalis* with the Mediterranean *P. orientalis*. Because of this mix, it is very tolerant of urban conditions. People plant it widely in cities like London and throughout the temperate world. It is a very hardy tree for park environments. It can even survive in areas with high pollution. The hybrid often backcrosses with its parent species in the wild.

Plane trees can also face challenges from various diseases. A fungal disease called anthracnose can cause trees to lose their leaves. This usually happens during cold and wet spring weather. *P. occidentalis* is quite susceptible to this, but *P. orientalis* is more resistant.

Another serious issue is a wilt disease called *Ceratocystis platani*. This disease is a major problem in much of Europe. While North American species are mostly resistant, Old World species are very sensitive to it. Other fungi, like powdery mildew or Massaria disease, can also affect the trees.

Finally, these trees can sometimes affect the people living near them. All parts of a *Platanus* tree have tiny, star-shaped hairs called trichomes. During long dry periods, strong winds can break these hairs off. This creates a fine dust that can irritate the eyes, nose, and throat. This irritation is sometimes called "platanus cough." It is not a true allergy, but a physical irritation from the dust. To stay safe, people can wear masks or protective glasses during windy, dry weather. Sweeping up fallen leaves in cities can also help reduce the dust.