Sequences of nuclear ribosomal DNA ITS and ETS regions were used to examine phylogenetic relationships of Syringa and Ligustrum. Twenty-seven samples were included in parsimony analyses, representing all major groups of these two genera. Two species of Fraxinus and one species of Jasminum were also included in analyses for rooting purposes. In the resulting phylogenetic hypothesis series Syringa (Syringa) diverges first and is followed by the monotypic series Pinnatifoliae (Syringa), which is sister to a clade containing the remaining species of Syringa and species of Ligustrum. However, this sister relationship is weakly supported. Our results support the recognition of monophyletic groups corresponding to subgenus Ligustrina, and series Syringa, Pubescentes, and Villosae, and suggest that Ligustrum as a monophyletic group is derived from within Syringa, such that Syringa as traditionally circumscribed is paraphyletic. Forcing Syringa to be monophyletic entails nine extra steps, which is significant, as judged by the Templeton test. Parasyringa sempervirens is phylogenetically embedded within the Ligustrum clade, supporting its placement in Ligustrum. Berries are a synapomorphy of Ligustrum species, and the dehiscent berry of Parasyringa sempervirens is likely to be an evolutionary reversal towards a capsule, which is characteristic of Syringa. The evolution of berries might have contributed to an accelerated rate of speciation in Ligustrum.

Communicating Editor: Jerrold Davis