Horse-Chestnut (Aesculus hippocastanum).
“In Britain and Ireland, the nuts are used for the popular children’s game conkers. During the First World War, there was a campaign to ask for everyone (including children) to collect horse-chestnuts and donate them to the government. The conkers were used as a source of starch for the fermentation via the Clostridium acetobutylicum method devised by Chaim Weizmann to produce acetone.”
“The common name “horse-chestnut” (often unhyphenated) is reported as having originated from the erroneous belief that the tree was a kind of chestnut (though in fact only distantly related), together with the observation that eating the fruit cured horses of chest complaints[ despite this plant being poisonous to horses.”