Fraxinus

The genus *Fraxinus* consists of plants commonly known as ash trees. These plants belong to the Oleaceae family, which is the olive family. There are between 45 and 65 different species within this genus. Most ash trees are deciduous, meaning they drop their leaves every autumn. However, some species living in subtropical regions are evergreen. These trees are found widely across Europe, Asia, and North America.

Ash trees have very specific physical characteristics. Their leaves are usually arranged in an opposite pattern on the stem. Most leaves are pinnately compound, which means they are divided into leaflets like a feather. The seeds are known as "keys," but they are botanically a type of single-winged fruit called a samara. Many species are also dioecious. This means that male and female flowers grow on entirely separate plants. The male flowers typically possess two stamens. If a calyx or corolla is present, it usually has four lobes or petals that are white or pale yellow.

Scientists have studied the classification of ash trees for centuries. Carl Linnaeus first described the genus *Fraxinus* in 1753. Since then, many other botanists have described different tree genera that were later found to be synonymous with *Fraxinus*. These include *Ornus*, described by Georg Rudolf Boehmer in 1760, and *Fraxinoides*, described by Friedrich Kasimir Medikus in 1791. Other names like *Mannaphorus*, *Calycomelia*, and *Meliopsis* were also proposed by various researchers. Today, the Angiosperm Phylogeny Group classifies *Fraxinus* within the order Lamiales, which is the mint order.

Fossil evidence shows that ash trees have a very long history on Earth. The oldest fossils clearly identified as *Fraxinus* come from the Middle Eocene period. These fossils date back 49 to 39 million years and were found in southeast North America. They include an extinct species called *F. wilcoxiana*. Other fossils show the movement of the genus over time. Fossil pollen of *F. angustifolia* is known from Europe during the Upper Miocene, about 12 million years ago. Additionally, winged fruits of *F. oishii* were discovered in Korea from the Middle Miocene.

Ash wood is highly valued because it is both strong and elastic. The density of the wood varies by species. For example, the white ash, or *F. americana*, has a density of around 670 kg/m3. The European ash, or *F. excelsior*, is even denser at 710 kg/m3. Because the wood is resilient, it is used for tool handles and agricultural implements. It is also used to make furniture, bowls, and spoons. The Morgan Motor Company in Great Britain even uses ash wood to manufacture frames for sports cars.

Music makers also rely on the unique properties of ash. The wood is considered resonant, which helps it provide a balanced tone for high and low notes. This makes it an excellent choice for making drum shells. Since 1950, the Fender musical instrument company has used ash, including swamp ash, as a tonewood for electric guitars. Beyond music and industry, ash trees have deep roots in human culture. In Greek mythology, the Meliae were nymphs associated with ash trees. In Norse mythology, a massive ash tree called Yggdrasil sustained the nine worlds of the cosmos.

Despite their many uses, ash trees face serious ecological threats today. In North America, the emerald ash borer has caused massive damage. This wood-boring beetle was accidentally introduced from eastern Asia in the late 1980s or early 1990s. The larvae feed on the inner bark and the phloem. This process prevents the tree from transporting water and nutrients. This pest has killed tens of millions of trees across 22 United States states and parts of Canada. It currently threatens approximately seven billion ash trees in North America.

In Europe, a different threat exists in the form of a fungus. The fungus *Hymenoscyphus fraxineus* causes a disease known as chalara ash dieback. This disease has been particularly active in eastern and northern Europe since the mid-1990s. The impact is severe; for instance, the fungus has infected about 90% of the ash trees in Denmark. In 2012, the disease was also found in mature woodlands in the United Kingdom. While these threats are serious, researchers have looked into biological controls, such as native Asian wasps, to help manage the beetle populations.