Crossosomataceae are a group of shrubs from North America and Mexico, that includes four genera: Crossosoma , Apacheria , Forsellesia and Velascoa . Apacheria and Velascoa are monotypic. Relationships of the genera and monophyly of the family have not yet been tested. We evaluated these issues using rbcL chloroplast DNA sequence data. By analyzing the sequences of representatives of the four genera with that of the "Eudicots" we concluded that they constitute a monophyletic group and that their phylogenetic position corresponds with previous angiosperm phylogenies. A more restricted analysis with the most closely related taxa showed that Apacheria and Velascoa are closely related. They share morphological characters such as form and position of petals and fimbriate aril. Phytogeographical patterns are discussed. Velascoa is the only genus that reaches central Mexico pine-oak forests and it is not found in northern xerophytic habitats like the rest of the Crossosomataceae.

Key words: Crossosomataceae, molecular systematics, rbcL sequences