 In the first edition of his "Systema Naturae" (1735).Carl Linnaeus divided all three of his kingdoms of Nature (minerals, plants, and animals) into classes.Only in the animal kingdom are Linnaeus's classes similar to the classes used today; his classes and orders of plants were never intended to represent natural groups, but rather to provide a convenient "artificial key" according to his "Systema Sexuale", largely based on the arrangement of flowers.