Phylogenetic relationships within the Celastraceae were inferred from a simultaneous analysis of morphological characters and sequence-based characters from the 5' end of 26S nuclear ribosomal DNA, the first exon of phytochrome B, rbcL, and atpB. Two genera previously assigned to the Celastraceae, Forsellesia and Goupia, are resolved as members of the Crossosomataceae and the Goupiaceae, respectively. Lepuropetalon and Parnassia (Saxifragaceae) are resolved as members of an early-derived lineage within the Celastraceae. The Stackhousiaceae are resolved as a monophyletic group nested within the Celastraceae. Canotia is supported as the sister group of Acanthothamnus within the Celastraceae. Maytenus sensu lato is resolved as a polyphyletic assemblage with Gymnosporia and Tricerma derived from different lineages. Maytenus sensu stricto remains an unnatural genus that needs to be re-circumscribed. Cassine sensu stricto, endemic to South Africa, is supported as distinct from the large, widely-distributed genus Elaeodendron. Kokoona and Lophopetalum are resolved as "transitional genera" between the Celastraceae sensu stricto and the Hippocrateaceae. Plagiopteron (Plagiopteraceae) is supported as closely related to Hippocratea sensu lato. The Hippocrateaceae (including Plagiopteron and Lophopetalum) are supported as a monophyletic group nested within the Celastraceae. The classifications of the Celastraceae sensu stricto and the Hippocrateaceae by Loesener and Hallé, respectively, are not supported. Arils appear to have two independent origins within the Celastraceae and have been variously modified into mucilagenous pulp, seed wings, or lost.

Key words: 26S nuclear ribosomal DNA, Celastraceae, Celastrales, Hippocrateaceae, phytochrome B, Stackhousiaceae