An ash can be any of four different tree genera from four very distinct families; most commonly in a combined form (e.g., "mountain ash"; see end of page for disambiguation), but originally and most commonly refers to trees of the genus Fraxinus (from Latin "ash tree") in the olive family Oleaceae. The ashes are usually medium to large trees, mostly deciduous though a few subtropical species are evergreen. The leaves are opposite (rarely in whorls of three), and mostly pinnately-compound, simple in a few species. The seeds, popularly known as keys or helicopter seeds, are a type of fruit known as a samara. The genus Fraxinus contains 45-65 species. The tree's common English name goes back to the Old English æsc, a word also routinely used in Old English documents to refer to spears made of ash wood.
The emerald ash borer Agrilus planipennis, a wood-boring beetle accidentally introduced to North America from eastern Asia with ash wood products circa 1998, has killed millions of trees in the Midwestern US and adjacent Ontario, and some isolated smaller areas on eastern North America. It threatens some 7 billion ash trees in North America. The public is being cautioned not to transport unfinished wood products, such as firewood, to slow the spread of this insect pest.
It is also often used as material for electric guitar bodies and, less commonly, for acoustic guitar bodies, known for its bright, cutting tone and sustaining quality. They are also used for making drums shells.
Ash veneers are extensively used in office furniture. It also makes excellent firewood. The two most economically important species for wood production are White Ash in eastern North America, and European Ash in Europe. The Green Ash is widely planted as a street tree in the United States. The inner bark of the Blue Ash has been used as a source for a blue dye. The cortex (bark) of Fraxinus rhynchophylla HANCE Fraxinus chinensis ROXB. Fraxinus szaboana English and Fraxinus stylosa English are used in Traditional Chinese Medicine (TCM) for diarrhea, dysenteric disorder, and vaginal discharge. It is also good for the eyes where there is symptoms of redness, swelling, and pain. The dosage is 6-12 grams.
In Norse mythology, the World Tree Yggdrasil is commonly held to be an ash tree, and the first man, Ask, was formed from an ash tree. Elsewhere in Europe, snakes were said to be repelled by ash leaves or a circle drawn by an ash branch. Irish folklore claims that shadows from an ash tree would damage crops. In Cheshire, it is said that ash could be used to cure warts or rickets. See also the letter ash.
In Greek mythology, the Meliai were nymphs of the ash, perhaps specifically of the Manna Ash (Fraxinus ornus), as dryads were nymphs of the oak. Many echoes of archaic Hellene rites and myth involve ash trees.