An ash can be any of four different tree genera from four very distinct families (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, are a type of fruit known as a samara. 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.