An order of flowering plants, division Magnoliophyta (Angiospermae) in the subclass Hamamelidae of the class Magnoliopsida (dicotyledons). The order consists of a single family, genus, and species (Leitneria floridana) of the southeastern United States. The plants are simple-leaved, dioecious shrubs with the flowers in catkins. The ovary is superior and pseudomonomerous, with a single ovule ripening into a small drupe.