The phylogeny of Gentianella (Gentianaceae) and its colonization of the southern hemisphere as revealed by nuclear and chloroplast DNA sequence variation

The generic circumscription and infrageneric phylogeny of Gentianella was analysed based on matK and ITS sequence variation. Our results suggested that Gentianella is polyphyletic and should be limited to species with only one nectary per petal lobe. Gentianella in such a circumscription is most closely related to one part of a highly polyphyletic Swertia. Within uninectariate Gentianella two major groups could be recognized: 1) northern hemispheric species with vascularized fimbriae at the base of the corolla lobes, and 2) northern hemispheric, South American, and Australia/New Zealand species without vascularized fimbriae. When fimbriae are present in this latter group, they are non-vascularized. Whereas ITS data suggested a sister group relationship between the fimbriate and efimbriate group, the matK data suggested paraphyly of the efimbriate group with Eurasian efimbriate species as sister to the remainder of the clade. Based on the phylogeny and using geological and fossil evidence and a molecular clock approach, it is postulated that the efimbriate lineage originated in East Asia near the end of the Tertiary. From East Asia it spread via North America to South America, and from there it reached Australia/New Zealand only once by a single long distance dispersal event. The place of origin of the fimbriate lineage remained doubtful. The high specific diversity of Gentianella in South America probably resulted mainly from the availability of a very large alpine area open to colonization rather than from particularly high speciation rates in comparison to other taxa.