Conkers splashing in water. High-speed photograph of three conkers splashing underwater. Conkers are the seeds of the horse chestnut tree (Aesculus hippocastanum). On the tree, they are encased in a prickly covering, within which is the hard brown seed or conker. They are used in the traditional British children's game of conkers. A wake of air bubbles shows the path of each conker after it entered the water.