Analysis of the trnT-trnL spacer, the trnL intron and the trnL-trnF spacer of 65 species of Cynanchum, 33 members of the Metastelminae, and seven representatives of other Asclepiadeae shows that Cynanchum in its present circumscription is polyphyletic. Both the genus Cynanchum and the subtribe Metastelminae s.l. split along the Old World—New World geographic division. The only exception to this division is Cynanchum subgenus Mellichampia, which belongs to Cynanchum s. str. For the Old World Cynanchum relatives, the subtribe Cynanchinae is re-established. The remaining New World sections of Cynanchum are not monophyletic. The South American members of section Cynanchum join the morphologically aberrant Grisebachiella hieronymi. Section Macbridea is associated with Funastrum. In the Old World, the succulent genera Folotsia, Karimbolea, Platykeleba, and Sarcostemma are monophyletic with stem-succulent Cynanchum and nested within a clade of exclusively Malagasy Cynanchum species.

Communicating Editor: Gregory M. Plunkett