Caltha consists of ten species of perennial herbs found in the moist temperate and cold regions of both hemispheres. Past treatments had divided the genus into two sections based primarily on the presence of distinctly inflexed leaf auricles in the Southern Hemisphere species. Through a cladistic analysis of three DNA sequence data sets and morphology, we evaluate this classification as well as biogeographical implications and character evolution. We find that Caltha natans (N. America, Asia) is sister to all other species; Caltha palustris (circumboreal) and Caltha scaposa (Asia) are well supported as sister; and Caltha leptosepala (western N. America) and the Southern Hemisphere species together form a well supported group. We suggest a historical dispersal event from North to South America, with a subsequent dispersal event to New Zealand and Australia. A reexamination of leaf morphology supports this hypothesis.

Key words: biogeography, Caltha, Ranunculaceae