Results from molecular studies using sequence data from the chloroplast gene ndhF have provided new insights on the phylogenetic relationships within the mostly tropical North American Celastraceae. The traditional classification of the family is not supported by this data as most subfamilies are revealed to be paraphyletic. The ruderal, moist forest genus Perrottetia is basal to all Celastraceae sampled. The families Canotiaceae and Hippocrateaceae traditionally allied to or included within the Celastraceae are strongly nested within the family. Hippocratea is sister to Mortonia whereas Salacia, the other Hippocrateaceae sampled, is nested in the same clade along with Cassine, Crossopetalum, Orthosphenia, Rzedowskia, and Schaefferia; the Asiatic genus Trpterygium is basal to this group of mostly xerophytic, North American genera. The southern Chihuahuan desert/Tehuacan valley endemic genus Acanthothamnus which shares a similar growth form with Canotia, is revealed as sister to Canotia. The genus Wimmeria and Zinowiewia, the only two representatives of subfamily Tripterygioideae in North America are nested in different clades. Wimmeria is sister to Canotia and Acanthothamnus. This result, along with other morphological data, supports a xerophytic origin of the genus Wimmeria. The cloud forest genera Zinowiewia and Microtropis are sister and not closely related to Wimmeria or any other member of subfamily Tripterygioideae. These results highlight the strong need for a reevaluation of the classification of the family and provide a framework for future molecular and morphological studies of the Celastrales.

Key words: Canotiaceae, Celastraceae, Hippocrateaceae, ndhF, Wimmeria