As he noted in 1981, more than half of the species are found in the Ranunculaceae. The membership of the order, and even the definitions of the families, has long been unstable. Even today, little has changed.
Most authors regard Ranunculaceae as the basal element within the order.
Where Thorne has Ranunculales, Takhtajan has Lardizabalales, Menispermales, Berberidale, Ranunculales, Circaeasterales, Hydrastidales and Papaverales. All of these families form a distinct core with Cronquist defining the Ranunculales and Papaverales as those basically terrestrial members of the Magnoliidae without ethereal oil cells and with triaperaturate pollen. The curious addition are the Eupteleaceae, a taxon I feel belong the the Hamamelididae, not the Ranunculidae, in their own order, the Eupteleales, adjacent to the Cercidiphyllales. Thorne puts them next to the Cerciphyllaceae in his broadly defined Hamamelidales. The ranunculoid angiosperms present an additional problem that is only now being addressed.