The species Æsculus hippocastanum or "Horse Chestnut" tree, from the family Sapindaceae is common throughout Britain and many countries. Similar to the popular edible "Sweet Chestnut" (Castanea sativa and other Castanea), the game using the horse chestnut's small hard fruit ("conker") has been a thing of obsession in the playground for generations in Britain. The fruit has been known as Horse Chestnut for hundreds of years after its sharp, bitter tasting fruit. It is not just the fruit but leaves and flowers that are unpleasant. All these contain the triterpene saponin or glycoside (and glucoside) known as "Aesculin". This chemical when ingested results in severe gastroenteritis at most due its poor absorbance into the bloodstream. However, with larger consumptions, lack of coordination, twitching, restlessness, depression, vomiting, diarrhoea, muscle weakness, and occasionally paralysis and unconsciousness or worse. It is present throughout the tree mostly in the leaves, together with a complex mixture of other compounds in different parts of the plant. One such chemical collection (mixture of acetylated glycosides) is the saponin aescin.
Both Aesculin and Aescin however are used in homeopathic medicine. Aesculin is used to thin the blood improving its viscosity aiding its passage back to the heart. Used in conjunction with Aescin which decreases permeability of the veins to fluids is used to treat the potentially but, in most cases, just painful "Varicose Veins" and Haemorrhoids. This is a useful medication therefore in relieving the pain and appearance, and prevent possible clotting and blocking of veins (may have then occasionally lead to stroke or heart problems). Other natural extracts ("tonic herbs") are then added in addition to the other compunds present in horse chestnut (flavinoids, glycosides, saponins), to soothe and aid healing. Aesculin and Aescin are used in a wider range of homeopathic treatments.
Horse Chestnut is not the only plant to contain such chemicals. White Hawthorn (Crataegus oxyacantha), Ash (Fraxinus...), Sweet Bursaria (Bursaria spinosa) all contain Aesculin in varying concentrations, predominatly in the leaves of Bursaria as with Horse Chestnut , and the bark of Ash.