Shrub to small tree 10 to 35’ tall. Not to be confused with the American Hophornbeam (Ostrya americana), American Hornbeam has a single, crooked trunk and a broad rounded crown, with rough, slate-colored bark on older trees, and narrow, serrated leaves. American Hornbeam is monoecious, with male and female flowers on the same individual. The male flowers are drooping catkins located on the tips of twigs. The female flowers are short, hairy, and arranged in pairs. Blooming occurs during mid to late spring, and flowers are wind-pollinated. American Hornbeam produces large numbers of nutlets which ripen from late summer to fall and are dispersed by mammals and birds.
American Hornbeam is a host plant for the caterpillars of several species of butterflies, including the Eastern Tiger Swallowtail, the Striped hairstreak, and the Red-spotted Purple. Nutlets and buds are an important food for gray squirrels and wild turkeys. Leaves, twigs, and larger stems are eaten by cottontails and white-tailed deer, though Hornbeam is not among their preferred foods. American Hornbeam is also heavily used by beaver due to its abundance in beaver habitat.
American Hornbeam is a shade-tolerant species, especially as a seedling. It can quickly and aggressively replace trees lost through logging in a wide variety of sites. Hornbeam grows mainly on moist sites with deep, rich soil and has thin bark and low tolerance of fire.
In the Arb:
Look for it in a few plantings in the Upper Arb.