XVI International Botanical Congess

The genus Centaurium (Gentianaceae) consists of about 50 species mostly annuals or biennials. Two regions of diversification are actually recognized. In the Mediterranean area, both diploid and tetraploid species occur whereas in the western part of North America and Mexico only polyploids species are found. We have investigated the phylogenetic relationships within this group for the majority of the species using sequences of nrDNA (ITS) and cpDNA (trnL intron). Moreover, we also stated a large survey of chromosome numbers of different population of the New World species in order to understand the caryological evolution of the group. Phylogenetic analysis strongly supports the existence of at least four American clades traducing a pattern of evolution from Californian to Texan and Mexican species. We also found new chromosome numbers in different American species which support the parttern of evolution shown by molecular data. Eurasian and New World species form clearly distinct groups suggesting an early separation between these taxa. Moreover our study showed that both hybridization and amphiploidy are important source of diversification within Centaurium. Finally, this work will result in the revision of the known classification of the genus.