The genus Fraxinus, the Ashes, in Oleaceae, consists of about 50 tree and shrub species. The most recent classification of the genus by Lingelsheim (1920) identified two sections: Ornus (subsections Euornus and Ornaster), and Fraxinaster (subsections Dipetalae, Pauciflorae, Sciadanthus, Melioides, and Bumelioides). Ornus is characterized by terminal inflorescences, insect pollinated Euornus have showy petalous flowers and wind pollinated Ornaster are apetalous. The species of section Fraxinaster are wind pollinated and characterized by apetalous flowers in lateral inflorescences (except F. dipetala that has two petals). The two main subsections Melioides and Bumelioides differ in that both calyx and corolla are wanting in Bumelioides. In an attempt to establish phylogenetic relationships among all species of Fraxinus, DNA sequences from the nuclear ITS region in 94 specimens, representing 43 of the 49 presently recognized taxa of the genus, were analyzed by cladistic methods. The result shows that three major and two smaller clades can be distinguished, roughly corresponding to Lingelsheim's subsections, but relationships between them depend heavily on the choice of outgroup: (1) Old World subsection Bumelioides, including North American F. nigra as sister to F. mandshurica and F. platypoda. F. xanthoxyloides, in monotypic Sciadanthus, is sister to Bumelioides. (2) New World subsection Melioides and F. cuspidata. (3) Xerophytic New World Pauciflorae. (4) F.dipetala, in monotypic Dipetalae, is joined by F. anomala and F. quadrangulata in a strongly supported clade, sister group to the rest of Fraxinus in some of the trees. (5) Section Ornus is clearly monophyletic, but its subsection Euornus is paraphyletic because subsection Ornaster is derived from it. Section Fraxinaster, as circumscribed by Lingelsheim, is paraphyletic no matter how the cladograms are rooted. Thus, in Fraxinus, wind pollination appears to be ancestral and insect pollinated species are derived, and within the insect pollinated group, adaptations to wind pollination have evolved again.

Key words: anemophily, Fraxinus, ITS, Oleaceae, phylogeny, wind pollination