is a genus of flowering plants in the olive and lilac family, Oleaceae. It contains 45-65 species of usually medium to large trees, mostly deciduous though a few subtropical species are evergreen.
The tree's common English name, ash, goes back to the Old English æsc, while the generic name originated in Latin. Both words also meant "spear" in their respective languages.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. Rowans or Mountain Ashes are unrelated to true ashes and belong to the Genus Sorbus though the leaves and buds are superficially similar.