Aesculus hippocastanum is a species of flowering plant in the soapberry and lychee family Sapindaceae. It is a large deciduous, synoecious  (hermaphroditic-flowered) tree, commonly known as horse-chestnut or conker tree.
Aesculus hippocastanum is a large tree, growing to about 39 metres (128 ft) tall:371 with a domed crown of stout branches; on old trees the outer branches are often pendulous with curled-up tips. The leaves are opposite and palmately compound, with 5–7 leaflets; each leaflet is 13–30 cm long, making the whole leaf up to 60 cm across, with a 7–20 cm petiole. The leaf scars left on twigs after the leaves have fallen have a distinctive horseshoe shape, complete with seven “nails”. The flowers are usually white with a yellow to pink blotch at the base of the petals; they are produced in spring in erect panicles 10–30 cm tall with about 20–50 flowers on each panicle. Usually only 1–5 fruit develop on each panicle; the shell is a green, spiky capsule containing one (rarely two or three) nut-like seeds called conkers or horse-chestnuts. Each conker is 2–4 cm diameter, glossy nut-brown with a whitish scar at the base.