The chestnut is the fruit of the chestnut tree, unlike the horse chestnut which is instead a seed. Chestnuts derive from female flowers (usually 2 or 3) enclosed by a dome which then turns into a hedgehog. The chestnut is an achene, has a smooth and dark brown leathery pericarp, at the apex there is the so-called torch, that is the remains of the styluses, while at the base there is a lighter scar called the hilus.
The shape of the fruit depends not only on the variety of chestnuts, but also on the number and position they occupy within the outer hedgehog
hemispherical for the lateral fruits and flattened for the central one; empty, aborted, flattened fruits are called guscioni.