Complex sentence: A walnut is the nut of any tree of the genus "Juglans" (Family Juglandaceae), particularly the Persian or English walnut, "Juglans regia" used for food after being processed while green for pickled walnuts or after full ripening for its nutmeat.
Split into simpler sentences: A walnut is the nut of any tree of the genus "Juglans" (Family Juglandaceae), particularly the Persian or English walnut, "Juglans regia". It is used for food after being processed while green for pickled walnuts or after full ripening for its nutmeat.