Elm

The elm is a tall tree.

It grows in many lands. Some elms grow very big.

They have green leaves. The leaves grow on the branches.

The tree makes small seeds. The wind helps carry the seeds. Some trees have a shape like a vase. A sickness has hurt many elms. This sickness comes from tiny bugs. People are making new trees to stay strong. These new trees can grow in parks again.

Elm trees are tall and strong.

They grow in many parts of the world. You can find them in North America and Eurasia. Some elms grow very large. The American elm can grow quite high. These trees often have a vase shape.

This means the branches spread out wide.

Elm leaves have jagged edges. The tree makes small seeds called samaras. These seeds are very light. The wind carries them to new places.

Many elms have faced a big problem. A sickness called Dutch elm disease has killed many trees. This sickness comes from a microfungus, which is a tiny living thing. Bark beetles carry the fungus to the tree. When the fungus enters the tree, it blocks the flow of water. This makes the tree sick. To help, people have made new types of elms. These new trees can fight the sickness. This helps elms grow in parks and forests again.

Elm trees are important parts of many natural forests.

They grow in many places across the Northern Hemisphere. You can find them in North America and Eurasia. They also live in parts of Africa and Southeast Asia. Many people planted them in gardens and parks long ago. Some elms can grow to be very large and old.

The American elm is known for growing quite high. It often has a forked trunk that looks like a vase.

Elms have a special way of making new trees. The flowers are small and do not have petals. Instead of bees, the wind helps move the pollen.

After pollination, the tree makes a fruit called a samara. These samaras are very light and thin. They are designed to be carried away by the wind. Some British elms have 50,000 of these seeds in just one pound.

The seeds even use sunlight to make energy before the leaves appear. This helps the new plant get a head start.

Scientists who study elms have a special name. They are called pteleologists. This name comes from a Greek word for elm.

The history of these trees goes back a long time. The oldest elm fossils are leaves from the Paleocene period. There are about 30 to 40 different species of elm. It can be hard to tell them apart because they mix easily. Most of the different kinds are found in Asia.

In recent years, elms have faced a hard job. A sickness called Dutch elm disease has killed many mature trees. This disease is caused by a microfungus. Small bark beetles carry the fungus from tree to tree. When the fungus enters a wound, it moves into the tree's plumbing. This blocks the flow of water from the roots to the leaves.

Because of this, many elms in Europe and North America died.

Even with this sickness, people are working to help elms. Scientists have developed new types of elms that resist the disease.

These new trees can be planted in forests and parks again. You might also see elms used in different ways. Some people grow them from cuttings or by grafting. Grafting is when parts of different trees are joined together. This can help a tree grow stronger or stay small.

Elms remain a very important part of our world.

Elms belong to the genus *Ulmus* within the family Ulmaceae. These deciduous or semi-deciduous trees are vital components of many natural forests. They are distributed widely across most of the Northern Hemisphere. You can find them in the temperate and tropical-montane regions of North America and Eurasia. Their range also extends south into Western Asia, Africa, and Southeast Asia.

Elm trees have a unique way of reproducing through wind pollination. The genus is hermaphroditic, meaning the flowers contain both male and female parts. These flowers are apetalous, which means they lack petals. After pollination, the tree produces a fruit known as a samara. The samara is a round, wind-dispersed seed structure. These seeds are often flushed with chlorophyll. This allows them to perform photosynthesis before the tree's leaves even emerge.

Samaras are designed for efficient travel through the air. They are incredibly light and thin. For example, British elms can produce around 50,000 samaras per pound. While most have two wings, rare anomalies can result in more.

Elms are generally tolerant of various soil types and pH levels. However, most species require soil with good drainage to thrive. The American elm is particularly notable for its size. It can grow to great heights, often featuring a forked trunk that creates a vase-like profile.

Taxonomy, or the science of classification, is complex for elms. There are approximately 30 to 40 recognized species. This ambiguity exists because elms hybridize, or mix, very easily. This makes it difficult for scientists to define clear boundaries between species. Asia holds the greatest diversity, with about two dozen species. In contrast, only eight species are endemic to North America.

Botanists who specialize in the study of elms are called pteleologists. This title is derived from the Greek word *ptelea*, meaning elm.

Elm history stretches back to the Paleocene epoch. The oldest known fossils of the genus are elm leaves. In more recent history, elms were widely planted for beauty. During the 19th and early 20th centuries, they were used as ornamental trees. They decorated streets, gardens, and parks across Europe and North America.

They were even common in parts of the Southern Hemisphere, such as Australasia.

In the late 20th century, elms faced a massive threat from Dutch elm disease. This disease is caused by a microfungus. It is spread by vectors, which are organisms that carry the pathogen. In this case, two species of *Scolytus* elm-bark beetles carry the fungus. When beetles create wounds in a tree, the fungal spores enter the xylem. The xylem is the part of the tree's vascular system that moves water. The tree responds by producing tyloses, which are growths that block the flow of water from roots to leaves.

Two main strains of the fungus have caused devastation. The first, *Ophiostoma ulmi*, arrived in Europe from Asia in 1910. It was introduced to North America in 1928. However, a second, more virulent strain called *Ophiostoma novo-ulmi* emerged later. This strain had a much more destructive impact on North American elms.

While many native species are susceptible, some Asiatic species have evolved resistance. Scientists are now developing disease-resistant cultivars to restore elms to our landscapes.

Elms also face other biological challenges. Elm phloem necrosis, often called "elm yellows," is an aggressive disease. It is caused by phytoplasmas that infect the phloem, or inner bark. This infection can girdle the tree, stopping the flow of nutrients.

Additionally, pests like the elm leaf beetle can decimate foliage. While these insects rarely kill the tree, they cause significant damage. Despite these threats, humans continue to propagate elms through grafting and cuttings to preserve their presence in our world.