LI, JIANHUA1,2,3*, JOHN H. ALEXANDER III1, and DONGLIN ZHANG2. 1Arnold Arboretum of Harvard University, 125 Arborway, Jamaica Plain, MA 02130; 2Department of Biosystems Science and Engineering, 5722 Deering Hall, Orono, ME 04469; 3Department of Plant Biology, University of New Hampshire, Durham, NH 03824. - The genus Syringa (Oleaceae) is paraphyletic: evidence from sequences of nuclear ribosomal DNA ITS and ETS regions.
Sequences of nuclear ribosomal DNA ITS and ETS regions were used to
examine phylogenetic relationships of Syringa and
Ligustrum. Thirty 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. Species of series Vulgares
(Syringa) and the monotypic series Pinnatifoliae
(Syringa) are basal clades followed by a clade containing
Ligustrum species and the remaining Syringa species.
Species of Ligustrum form a well-supported clade, which is
sister to a clade containing the rest of species of Syringa,
including subgenus Ligustrina, and series Pubescentes
and Villosae. All these groups are monophyletic. Parasyringa
sempervirens is phylogenetically embedded within the
Ligustrum clade, supporting its placement in Ligustrum.
Our results indicate that Ligustrum is derived from within
Syringa, suggesting that Syringa as traditionally
circumscribed is paraphyletic. Berries are a synapomorphy of
Ligustrum species, and the dehiscent berry of Parasyringa
sempervirens is an evolutionary reversal to a capsule, which is
characteristic of Syringa. The evolution of berries might have
resulted in an accelerated speciation in Ligustrum.
Key words: ETS, ITS, Ligustrum, Oleaceae, paraphyly, phylogeny, Syringa