To understand flower morphological evolution in Gentianaceae-Swertiinae, we studied generic relationships using trnL intron, matK, and nuclear ITS sequences of a total of 13 genera and 59 species of the subtribe. The phylogenetic incongruencies between the chloroplast and nuclear genes are likely to be the result of long branch attraction. The East Asian Megacodon and Latouchea and the eastern North American Bartonia and Obolaria were determined as the most basal genera, and several well-supported subgroups were revealed. Swertia, Lomatogonium, and Gentianella s. l. were highly polyphyletic and the position of Veratrilla and several species was ambiguous. The main flower types found in Swertiinae can be transformed into each other by simple developmental variation in proportion. This apparently happened several times during the evolution of Swertiinae and, in conjunction with other homoplastic characters, explains the difficulty of recognizing generic limits and the mosaic pattern of character distribution. Phylogenetic relationships, extant distribution ranges, and a preliminary molecular clock approach led to the hypothesis that the last common ancestor of the Swertiinae lived approximately 15 mya, and that an exchange of lineages between East Asia and North America happened frequently from the time of origin until only recently.

Communicating Editor: Thomas G. Lammers