This deciduous tree grows to a height of 15 to 25 metres and forms a broadly spreading crown. The bark is red-brown to grey-brown and scaly. The tree's brown buds are large and sticky to prevent damage by small insects, and burst to reveal the tree's distinctive palmate leaflets. The leaves are vivid green, generally turning warm yellow to golden yellow in autumn. The flowers, which appear in early May, are arranged in upright conical panicles. They are usually white, sometimes pink or red, and curly on the margins. In late September the mature fruits fall, their green spiny shells splitting to reveal one to three shiny brown inedible nuts, popularly known as conkers. The name horse chestnut comes from the leaf scars left on the twigs when the leaves fall. The scars have a distinctive horseshoe shape, complete with seven "nails".
The horse chestnut is only distantly related to the sweet chestnut, which bears edible fruits. It is native to a small area in the Pindus Mountains and Balkan mixed forests of South Eastern Europe. Horse chestnuts are commonly planted in parks and along streets and roads throughout Europe.