(Cycadeoidales) An extinct order of gymnosperms known from fossils extending throughout the Mesozoic era. They resembled cycads in habit and in leaf structure but can be distinguished from fossil cycads by certain features of the leaf epidermis, notably the possession of a *syndetocheilic
stomatal complex as compared to the *haplocheilic
stomata of the cycads. Like the cycads, they may have originated from the Pteridospermales.