Castanea dentata is a rapidly-growing deciduous hardwood tree, historically reaching up to 30 metres (98 ft) in height, and 3 metres (9.8 ft) in diameter. It ranged from Maine and southern Ontario to Mississippi, and from the Atlantic coast to the Appalachian Mountains and the Ohio Valley. C. dentata was once one of the most common trees in the Northeastern United States. In Pennsylvania alone, it is estimated to have comprised 25–30% of all hardwoods. The tree's huge population was due to a combination of rapid growth and a large annual seed crop in comparison to oaks which do not reliably produce sizable numbers of acorns every year. Nut production begins when C. dentata is 7–8 years old.
There are several similar chestnut species, such as the European sweet chestnut (C. sativa), Chinese chestnut (C. mollissima), and Japanese chestnut (C. crenata). The American species can be distinguished by a few morphological traits, such as leaf shape, petiole length and nut size. For example, it has larger and more widely spaced saw-teeth on the edges of its leaves, as indicated by the scientific name dentata, Latin for "toothed". According to a 1999 study by American Society for Horticultural Science, the Ozark chinkapin, which is typically considered either a distinct species (C. ozarkensis) or a subspecies of the Allegheny chinkapin (C. pumila subsp. ozarkensis) may be ancestral to both the American chestnut and the Allegheny chinkapin. A natural hybrid of Castanea dentata and Castanea pumila has been named Castanea × neglecta.
The leaves, which are 14–20 cm (5.5–8 in) long and 7–10 cm (3–4 in) broad, also tend to average slightly shorter and broader than those of the sweet chestnut. The blight-resistant Chinese chestnut is now the most commonly planted chestnut species in the US, while the European chestnut is the source of commercial nuts in recent decades. It can be distinguished from the American chestnut by its hairy twig tips which are in contrast to the hairless twigs of the American chestnut. The chestnuts are in the beech family along with beech and oak, but are not closely related to the horse-chestnut, which is in the family Sapindaceae.
The chestnut is monoecious, producing many small, pale green (nearly white) male flowers found tightly occurring along 6 to 8 inch long catkins. The female parts are found near base of the catkins (near twig) and appear in late spring to early summer. Like all members of the family Fagaceae, American chestnut is self-incompatible and requires two trees for pollination, which can be any member of the Castanea genus.
The American chestnut is a prolific bearer of nuts, usually with three nuts enclosed in each spiny, green burr, and lined in tan velvet. The nuts develop through late summer, with the burrs opening and falling to the ground near the first fall frost.
The American chestnut was a very important tree for wildlife, providing much of the fall mast for species such as white-tailed deer and wild turkey and, formerly, the passenger pigeon. Black bears were also known to eat the nuts to fatten up for the winter. The American chestnut also contains more nitrogen, phosphorus, potassium and magnesium in its leaves when compared to other trees that share its habitat. This means they return more nutrients to the soil which helps with the growth of other plants, animals, and microorganisms.