Arisaema comprises 130-150 species, most of them in the Sino-Himalayan region. Three occur in North America and Mexico, nine or ten in East Africa, and the most widespread species, A. flavum, ranges from Ethiopia across the tip of Arabia to Tibet. Based on sequences from cpDNA spacers and introns (trnL-F, rpl20-rps12, psbA-trnH), we identified the temperate East Asian Pinellia from among 17 closely related genera of Areae/Colocasieae as the sister group of Arisaema. Arisaema has so far been sampled for 51 species that represent its geographic range and ten of its eleven sections (Murata 1984, 1990, 1991), including most sections' types. As predicted from morphology, North American Arisaema are unrelated, and the genus thus appears to have crossed Beringia at least twice. Several sections appear polyphyletic, most clearly section Tortuosa, which includes the American A. dracontium. The single African species sequenced so far is sister to a species from Nepal and not to A. flavum, with which it overlaps in range, suggesting multiple former links across Arabia and supporting their assignment to different sections. Like all Aroideae, Arisaema is monoecious, but male and female function are usually separated by one or more years, depending on nutrient status, with several reversals possible during a plant's lifetime. Such sex change is unknown in other Araceae, inviting speculation about conditions that may have favored the evolution of this life history strategy in Arisaema.

Key words: Araceae, Arisaema, Beringia, biogeography, Pinellia, sex change