hornbeam or ironwood, name in North America for two groups of trees of the family Betulaceae (birch family), native to the eastern half of the continent. Carpinus caroliniana, also called blue beech and water beech, has smooth gray bark. The hop hornbeam, Ostrya virginiana, has thin, narrowly ridged, light-brown bark. The strong, heavy wood of both species is used for tool handles, mallets, and vehicle parts. Many valuable hardwood timber trees of other families are called ironwood, especially in Australia and in the Old World tropics. Hornbeams are classified in the division Magnoliophyta, class Magnoliopsida, order Fagales, family Betulaceae.