To search for the sister taxon of Acacia s.s. (tribe Acacieae) and to further knowledge of the phylogeny of the related tribe Ingeae, we have sequenced two regions of nuclear ribosomal DNA (ITS and ETS). Sixty species from tribe Ingeae (26 genera), together with representatives from each of five lineages of tribe Acacieae, have been sampled. Ingeae and Acacia s.s. form a well supported clade, with a monophyletic Acacia s.s. nested within a paraphyletic Ingeae. Based on our sampling, the closest relative of Acacia s.s. is most likely one of the Australian species of the genus Paraserianthes s.l.: Paras. lophantha subsp. lophantha or Paras. toona. Related to Acacia s.s. and Paraserianthes s.l. is a group of Ingeae from Australia and South East Asia: Archidendron p.p., Archidendropsis, Pararchidendron, and Wallaceodendron. This study is a preliminary step in resolving the intergeneric relationships of tribe Ingeae. Genetic relationships within Ingeae appear to conform to morphological groups previously identified as genera and informal alliances; some notable exceptions are discussed.