The systematic position of the genus Hintonia Bullock within Rubiaceae has been controversial. Cladistic analyses of the chloroplast ribulose biphosphate carboxylase-oxygenase large subunit (rbcL) DNA sequences including a wide range of taxa from within and outside Rubiaceae have been conducted. These studies suggest that Hintonia is related to genera belonging to the Portlandia group forming a monophyletic clade that also includes members of the Chiococceae and Catesbaeae tribes in addition to Exostema (Pers.) Humb. & Bompl. Previous classifications do not entirely reflect the relationships suggested by the rbcL analyses. A combined analysis including rbcL and morphology provides the basis for the interpretation of the evolution of characters traditionally used in the taxonomy of the family. These characters include life form, presence/absence of raphides, flower arrangement, flower aestivation, unit of pollen dispersal, texture of the fruit, pattern of fruit dehiscence, and presence/absence of a wing on the seed. A morphological cladistic analysis with a greater sampling of the taxa likely to be related to Hintonia provides further evidence for the interpretation of the phylogenetic relationships of these genera and the evolution of additional characters. These characters include: pattern of wax deposition in the leaves, point of insertion of the stamens in the corolla, pollen aperture number and type, placentation and placenta characters, seed orientation and seed coat characters. The morphological studies suggest that only three species endemic to Mexico and Guatemala should be recognized within Hintonia.

Key words: character evolution, combined analysis, Hintonia, Portlandia group, rbcL, Rubiaceae