Another common name of this tree is Ironwood. It is easy to identify Hop Hornbeam from its attractive and persistent hop-like fruits. In Illinois, its closest relative is another medium-small tree, Carpinus caroliniana (American Hornbeam). This latter tree has very smooth bark on its trunk, even when it is fully mature. The fruiting structure of American Hornbeam is quite different from the inflated sacs of Hop Hornbeam; the nutlets of American Hornbeam are subtended by 3-cleft bracts that are flat and open.