Horse chestnuts are a species of flowering plant in the maple, soapberry, and lychee family Sapindaceae, also known as Aesculus hippocastanum. They are a large, deciduous, synoecious tree and are native to parts of southeastern Europe. The fruits of horse chestnuts contain seeds that resemble sweet chestnuts but have a bitter taste. Horse chestnut seed extract is promoted for chronic venous insufficiency, irritable bowel syndrome, male infertility, and other conditions. However, the raw seeds, bark, flowers, and leaves of horse chestnut are unsafe because they contain a toxic component called esculin. Standardized horse chestnut seed extracts, from which this component has been removed, appear to be safe for short-term use. Horse chestnuts should not be confused with sweet chestnuts, which are edible, as horse chestnuts are poisonous and can cause digestive problems such as abdominal pain, nausea, vomiting, and throat irritation if eaten.