 The unrelated Horse chestnuts (genus "Aesculus") are not true chestnuts but are named for producing nuts of similar appearance that are mildly poisonous to humans.Nor should they be confused with water chestnuts, which are tubers of an aquatic herbaceous plant in the sedge family Cyperaceae.Other species commonly mistaken for chestnut trees are the chestnut oak ("Quercus prinus") and the American beech ("Fagus grandifolia"), both of which are also in the Fagaceae.