Horse Chestnut - Also known in Britain and Ireland as a Conker Tree. The large seeds are collected by children to play the game conkers where they are threaded on a lace and smashed against each other to determine who's can last the longest! The horse chestnut is toxic but can be broken down by some grazing animals. The flower of the horse chestnut is beautiful when viewed closely as shown here. The tree flowers from May to June with white or pink flowers. More than one seed or conker can be produced from a single shell.