Fraxinus is a genus of flowering plants in the olive and lilac family. 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 is Ash. 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.
Ash trees are currently under attack in the Midwest by the Emerald Ash Borer, first appearing in Michigan, and spreading in every direction throughout the states. Treatment against the borer is very costly, and will probably only be attempted on campus with a few select trees. It must be continued for the life of the tree, thus ISU is embarking on a campaign to replace the ash trees with alternative varieties.