A major category in the taxonomic hierarchy, usually comprising groups of families thought to possess a degree of *phylogenetic
unity. Groups of similar orders are placed in classes. The Latin names of orders usually terminate in -ales, e.g. Rosales and Geraniales. However, some orders, which were erected prior to the compilation of the International Code of Botanical Nomenclature, end in -ae, e.g. Glumiflorae and Tubiflorae.