A koala bear isn’t actually a bear, it’s a marsupial. Whales aren’t fish, they’re mammals. Tomatoes aren’t vegetables, they’re fruit. Almost nothing is actually a nut. Peanuts, Brazil nuts, cashews, walnuts, pecans and almonds: none of them are really nuts (for the record, peanuts are legumes, Brazils and cashews are seeds, and the others are all droops). Hazelnuts and chestnuts are the exception: they are the elite, the “true” nuts.
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Source: Phys.org