Scientists have classified chestnut trees in the family of plants that includes the oaks and the beeches. There are four main types of chestnut trees in the genus Castanea: the American, European (sometimes called Spanish), Chinese, and Japanese chestnut trees. The American chestnut was once a common shade tree in North America. That was before the spread of a fungus disease called chestnut blight. The disease was accidentally brought in from Asia in the early 20th century. Almost all American chestnut trees died from the disease because they had little resistance to it.

A chestnut tree is usually tall. The largest reach about 100 feet (30 meters) in height. The bark is deeply grooved. The leaves are shiny green and oval-shaped, with pointed ends and saw-toothed edges. The flowers grow in long, upright clusters on a twig. The fruit is green with a spiny husk. Inside are two to three nuts, depending on the type of tree. Each nut has a smooth, brown shell. The nut meat is covered with a bitter, brown coat and is cream colored.

The evergreen trees called chinquapins are closely related to the chestnuts and bear a similar fruit. However, several other types of plants that are called chestnuts are not related to the true chestnuts. Among these are the horse chestnut trees, which bear nuts that are not usually eaten. There are also several kinds of water chestnuts. They are water plants that produce a nutlike fruit.