Using rbcL plastid DNA sequences, we evaluated monophyly and relationships of the genera of Crossosomataceae, which are a small group of shrubs from North America and Mexico: Crossosoma, Apacheria, Glossopetalon (Forsellesia), and Velascoa. Morphological characters that correspond to the phylogenetic patterns were examined. The analysis consisted of two steps. In the first, we analyzed the sequences of representatives of the four genera with those of over 500 species of eudicots. Based on these results, a second, restricted analysis with 25 taxa was conducted. Crossosomataceae are monophyletic and the four genera fell into a well-supported clade with representatives of Stachyuraceae and Staphyleaceae. Characters that mark Crossosomataceae are: microphyllous leaves (less than 5 cm long), solitary flowers with an apocarpous ovary and hypanthium, ventrally dehiscent follicles, and seeds with a fimbriate or irregular aril. A brief description of the family and an identification key for the genera are presented.
Communicating Editor: John V. Freudenstein