Plate from 18th century encyclopedia showing the Linnean classes and orders of flowers. The various classes illustrated are as follows; Dioecia, Polygamia, Chryptogamia. Linneaus's classes and orders of plants, according to his Systema Sexuale, were never intended to represent natural groups (as opposed to his ordines naturales in his Philosophia Botanica) but only for use in identification. They were used for that purpose well into the nineteenth century. Within each class were several orders.