A conker tree is another name for the horse chestnut tree (Aesculus hippocastanum) . The tree is native to Greece and Albania and was introduced to the United States in the 1740s because of its showy floral display. The tree can grow up to 40 meters tall and has distinctive large leaves with serrated leaflets. The tree produces glossy brown seeds called conkers, which are surrounded by a spiky green case. Conkers are inedible and mildly poisonous if consumed in excessive quantities. The seeds were used in France and Switzerland for whitening hemp, flax, silk, and wool and can also dye fabrics a sky-blue color. The most famous use of horse chestnut is in the game of conkers, which is a traditional childrens game in Great Britain and Ireland played using the seeds of horse chestnut trees.