The hornbeams (Carpinus) are a genus of relatively small hardwood trees, placed in the birch family Betulaceae, though some botanists separate it off together with the hazels (Corylus) and hop_hornbeams (Ostrya) into a segregate family Corylaceae. The 30_40 species occur across much of the north temperate regions, with the greatest number of species in east Asia, particularly China. Only two species occur in Europe, and only one in eastern North America.

The leaves are deciduous, alternate, and simple with a serrated margin, and typically vary from 3-10 cm in length. The flowers are wind-pollinated pendulous catkins, produced in spring. The male and female flowers are on separate catkins, but on the same tree (monoecious). The fruit is a small nut about 3-6 mm long, held in a leafy bract; the bract may be either trilobed or simple oval. There are typically 10-30 seeds on each seed catkin.

European Hornbeam seed catkins

The European Hornbeam (Carpinus betulus), is a small to medium sized tree, typically 10-20 m tall but occasionally reaching 30 m. It is native to most of Europe except for northern Britain and most of Scandinavia. The leaves are 5-9 cm long, and the seeds have a 3-4 cm long trilobed bract.

The Oriental Hornbeam (Carpinus orientalis) occurs in southeast Europe and southwest Asia, usually on hot dry sites at lower altitudes than C. betulus, and is a smaller tree, rarely over 10 m tall and often shrubby. It has small leaves, 3_5 cm long. The seeds differ from C. betulus in having a simple bract (not trilobed), about 2 cm long.

The Japanese Hornbeam (Carpinus japonica) is similar to C. orientalis in having unlobed seed bracts, but differs from it in having larger leaves, 8_10 cm long.

The North American species, American Hornbeam (Carpinus caroliniana) is similar to C. betulus in leaf size and shape. The seed bract is also trilobed, but less deeply than in C. betulus.

The wood of hornbeams is very hard, and not used much due to the difficulty of working it. Its hardness has however lent it to use for carving boards, tool handles, coach wheels and other situations where a very tough, hard wood is required.

Individual European Hornbeam seed (enlarged; whole seed plus wing 4 cm long). The asymmetry of the seedwing makes it spin as it falls, improving wind dispersal. The shape of the wing is important in the identification of different hornbeam species.

The common English name of "hornbeam" derives from the hardness of the wood (likened to horn) and the Old English beam, a tree (cognate with German "baum"). American Hornbeam is also occasionally known as blue-beech, ironwood, or musclewood; the first from the resemblance of the bark to that of the American Beech Fagus grandifolia, the other two from the hardness of the wood and the muscular appearance of the trunk respectively.