Ash trees are medium to large trees of the genus Fraxinus of the family Oleaceae (Olive-tree like). The family contains between 45 and 65 species. Some of them are evergreen, but most are deciduous. They grow in most parts of the world. The seeds are commonly known as "keys" in English. They are a type of fruit known as a . Most of the ash species have light-green, oval shaped, leaves. The central stem of the compound leaf has 9 – 13 leaflets (small leaves) in pairs, with one at the tip. There are no stalks to the side leaflets. The leaflets are pointed and toothed, with hairs on the lower surface. The leaves appear relatively late in spring, and are amongst the first to be shed in autumn.