This is a widely diverse genus of trees with compound, opposite leaves. Traditionally, may of the common species made nice landscape trees especially for wet areas. However, in 2002, an insect called the Emerald Ash Borer (EAB) was discovered in Michigan. The larvae of this pest which is thought to have come from China, burrows through the cambium layer of ash trees and, eventually, kills the tree.

As of 2010, over 20 million ash trees have been killed and, despite government efforts, it is spreading throughout the Midwest. As a result, ash trees are no longer recommended for use in the landscape and several states have banned their sales.