The peanut or groundnut (Arachis hypogaea) is a legume and produces nut-like fruits within protective shells.  Peanuts are a highly nutritious food source for man and animals, containing high amounts of oil and storage proteins (about 25%), many of which, particularly Arachins and Conarachins, are allergenic.  For people with a peanut allergy, even minor exposure in the nano-gram range can cause reactions from mild skin rashes to fatal anaphylactic shock.