title: Monophyly and relationships of the tribe Exaceae (Gentianaceae) inferred from nuclear ribosomal and chloroplast DNA sequences.
abstract: Both chloroplast trnL (UAA) intron and nuclear ribosomal ITS sequences highly confirmed the monophyly of the tribes of the Gentianaceae defined by the recent classification, and revealed the tribe Exaceae as a basal clade just next to the basal-most lineage, the tribe Saccifolieae. Within the tribe Exaceae, Sebaea (except Sebaea madagascariensis) appeared as the most basal clade as the sister group to the rest of the tribe. The Madagascan endemic genera Gentianothamnus and Tachiadenus were very closely related to each other, together standing as sister to a clade comprising Sebaea madagascariensis, Ornichia, and Exacum. The saprophytic genus Cotylanthera nested deeply inside Exacum. Sebaea madagascariensis was shown closer to the Madagascan endemic genus Ornichia than to any other sampled Sebaea species. Exacum appeared as the most derived taxon within this tribe. The topology of the phylogenetic trees conform with the Gondwana vicariance hypothesis regarding the biogeography of Exaceae. However, no evidence for matching the older relationships within the family to the tectonic history could be corroborated with various divergence time analyses. Divergence dating estimated a post-Gondwana diverging of the Gentianaceae about 50 million years ago (MYA), and the tribe Exaceae as about 40 MYA. The Mozambique Channel land-bridge could have played an important role in the biogeographic history of the tribe Exaceae.
authors.affiliation: Laboratory of Evolutionary Botany, Institute of Botany, University of Neuchâtel, Emile-Argand 11, Neuchâtel CH-2007, Switzerland. yong-ming.yuan@unine.ch
authors.forename: Yong-Ming
authors.initials: YM
authors.lastname: Yuan
authors.forename: Sébastien
authors.initials: S
authors.lastname: Wohlhauser
authors.forename: Michael
authors.initials: M
authors.lastname: Möller
authors.forename: Philippe
authors.initials: P
authors.lastname: Chassot
authors.forename: Guilhem
authors.initials: G
authors.lastname: Mansion
authors.forename: Jason
authors.initials: J
authors.lastname: Grant
authors.forename: Philippe
authors.initials: P
authors.lastname: Küpfer
authors.forename: Jens
authors.initials: J
authors.lastname: Klackenberg
mesh_terms: D000349:Africa; D001208:Asia; D001483:Base Sequence; D017931:DNA Primers; D018742:DNA, Chloroplast / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics; D019143:Evolution, Molecular; D029965:Gentianaceae / Q000235:genetics*; D005843:Geography; D008969:Molecular Sequence Data; D010802:Phylogeny; D011157:Population Dynamics; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D017931:DNA Primers; D018742:DNA, Chloroplast; D004275:DNA, Ribosomal