The genus Swertia consists of ca 130 species and is nearly cosmopolitan in its distribution. However, most of the species occur in temperate regions of the Northern Hemisphere. The circumscription of the genus is still debated, mainly because many morphological traits such as pollen and seed ornamentation, or various floral structures, are shared with species of closely related genera of Gentianeae-Swertiinae (e.g. Frasera, Lomatogonium, Halenia and Veratrilla). Moreover, at the infrageneric level, only partial and controversial classifications have been attempted. To clarify the evolutionary history of Swertia, we analyzed phylogenetically non-coding nrDNA (ITS) and cpDNA (trnL-F) sequences of a broad range of taxa representing nearly all the morphological and biogeographical diversity of the genus Swertia, and of taxa belonging to 9 closely related genera. These genera are scattered among Swertia species in the phylogenetic tree, suggesting that they should be viewed as sister groups of paraphyletic lineages of Swertia. Owing to the highest species diversity and the occurrence of taxa with the presumed ancestral characters, the mountains of southwest China are thought to be the cradle of subtribe Swertiinae. Our phylogenetic tree brings also some light on the biogeographic processes associated to the species radiation resulting in the actual diversity of taxa.

Key words: biogeography, Gentianaceae, phylogeny, Swertia