The chestnuts are a group of eight or nine deciduous trees and shrubs in the genus Castanea, in the beech family Fagaceae. They are native to temperate regions of the Northern Hemisphere. Chestnuts belong to the family Fagaceae, which also includes oaks and beeches. The four main species groups are commonly known as American, European, Chinese, and Japanese chestnuts. Chestnut trees are of moderate growth rate (for the Chinese chestnut tree) to fast-growing for American and European species. The chestnut fruit is contained in a spiny (very sharp) cupule 5–11 cm in diameter, also called "bur" or "burr." The burrs are often paired or clustered on the branch and contain one to seven nuts according to the different species, varieties, and cultivars. The chestnut fruit has a pointed end with a small tuft at its tip (called "flame" in Italian), and at the other end, a hilum – a pale brown attachment scar.
A nut is a fruit composed of a hard shell and a seed, which is generally edible.
There is an additional requirement in botany that the shell does not open to release the seed (indehiscent). In a general context, a wide variety of dried seeds are called nuts, but in a botanical context, only ones that include the indehiscent fruit are considered true nuts.