MANSION, GUILHEM. Institute of Botany, University of Neuchâtel, Emile Argand 11, 2007 Neuchâtel, Switzerland. - Phylogenetic position of the north and central american species of Centaurium (Gentianaceae) based on molecular data and chromosome numbers: evidence of an old-world origin.
The genus Centaurium (Gentianaceae) consists of about 50
species, mostly annuals or biennials, distributed in two main regions
of diversification. In the Mediterranean area, diploid to hexaploid
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 almost all the
species using sequences of nrDNA (ITS) and cpDNA (trnL-F region).
Moreover, we have stated a large survey of the chromosome numbers of
different population of the New World species. Phylogenetic analysis
strongly supports the existence of at least five geographic groups and
suggest a pattern of colonization from Eurasia to California followed
by a migration in Texas and Mexico. The caryological survey of the
American species comfort the evolutive scenario inferred from
molecular markers. New chromosome numbers for several species were
also found. In addition, our study provides some evidences of regular
hybridization process among different Centaurium species
followed by polyploidization. These results suggest that amphiploidy
is involved in the diversification of the genus as a speciation
process. Finally, this work will result in a systematic revision of
the known classification of the whole genus.
Key words: biogeography, Centaurium, Gentianaceae, ITS, phylogeny, trnL-F