The horse chestnut and buckeyes (Aesculus spp.) are various species of angiosperm trees in the family Hippocastaneae. There are about 20 species of trees and shrubs in this family, occurring widely in temperate, angiosperm forests of Europe, Asia, and North America.
The horse chestnut and buckeyes have seasonally deciduous, oppositely arranged, palmately compound leaves, which means that the five to seven leaflets all originate from the same place at the far end of the petiole. The margins of the leaflets are coarsely toothed. The horse chestnut and buckeyes have attractive, whitish flowers, occurring in showy clusters. The flowers of Aesculus species develop in the springtime from the large, over-wintering, sticky stem-bud, before the years' leaves have grown. The flowers produce large quantities of nectar, and are insect pollinated. The fruits of the horse-chestnut and buckeyes are greenish, leathery, spiny capsules containing one or two large, attractive, chestnut-brown seeds. These seeds are not edible by humans.
The horse chestnut (Aesculus hippocastanum) is a tree that can grow as tall as about 115 ft (35 m), and is native to Asia and southeastern Europe. The horse chestnut has been widely planted in North America as an ornamental tree, especially in cities and other residential areas. This species sometimes escapes from cultivation and becomes locally invasive, displacing native species from woodlands.
Several species of buckeyes are native to North America. Most species occur in hardwood forests of the eastern and central United States. The yellow buckeye (A. octandra) grows as tall as 98 ft (30 m) and can attain a diameter of almost 3.3 ft (1 m). The Ohio buckeye (A. glabra) and Texas buckeye (A. arguta) develop a characteristic, unpleasant odor when the leaves or twigs are crushed. The painted buckeye (A. sylvatica) and red buckeye (A. pavia) are relatively southeastern in distribution. The California buckeye (A. californica) is a shrub or small tree of drier foothill areas of the west coast of the United States.
These various, native species are of relatively minor economic importance for their wood, which has been used to manufacture boxes, furniture, musical instruments, and other products.
The fruits of the horse chestnut and buckeyes are eaten by various species of wild animals and some species of livestock. However, these fruits contain a chemical known as aesculin that is poisonous to humans if eaten in large quantities, and can cause death. The seeds of horse chestnut and buckeyes should not be confused with those of the true chestnuts (Castanea spp.), which are edible. (True chestnuts or sweet chestnuts are classified in the beech family, the Fagaceae.) However, it is reported that boiling or roasting the seeds of horse chestnut and buckeyes can remove or disable the aesculin, to provide a starchy food.
Some people attribute medicinal qualities to the fruits and flowers of the horse chestnut and buckeyes. In Appalachia, it is believed by some people that the seeds of buckeyes will help to prevent rheumatism, if carried around in your pockets. Various preparations of the seeds, flowers, and bark have also been used as folk medicines to treat hemorrhoids, ulcers, rheumatism, neuralgia, and fever, and as a general tonic.
Sometimes, children will collect the seeds of horse chestnut or buckeyes, drill a hole through the middle, and tie them to a strong string. The game of "conkers" involves contests in which these tethered seeds are swung at each other in turn, until one of the horse chestnuts breaks. Each time a particular conker defeats another, it is said to gain a "life." However, there are many variations of the rules of this game.