CHASSOT, PHILIPPE. Institut de Botanique, Université de Neuchâtel, Emile Argand 11, 2007 Neuchâtel, Suisse. - Phylogenetic position of the genus Swertia (Gentianaceae) in the subtribe Swertiinae.
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