Yuan Yong-Ming, Wohlhauser Sébastien, Möller Michael, Chassot Philippe, Mansion Guilhem, Grant Jason, Küpfer Philippe, Klackenberg Jens
Laboratory of Evolutionary Botany, Institute of Botany, University of Neuchâtel, Emile-Argand 11, Neuchâtel CH-2007, Switzerland.
Mol Phylogenet Evol. 2003 Sep;28(3):500-17. doi: 10.1016/s1055-7903(03)00068-x.
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.
叶绿体trnL（UAA）内含子和核糖体ITS序列均高度证实了近期分类所定义的龙胆科各部落的单系性，并揭示了Exaceae部落是紧挨着最基部谱系Saccifolieae部落的基部类群。在Exaceae部落中，Sebaea属（马达加斯加Sebaea除外）作为该部落其余部分的姐妹群，呈现为最基部的类群。马达加斯加特有属Gentianothamnus和Tachiadenus彼此关系非常密切，共同作为包含马达加斯加Sebaea、Ornichia和Exacum的一个类群的姐妹。腐生属Cotylanthera深深地嵌套在Exacum属内部。马达加斯加Sebaea比其他任何采样的Sebaea物种更接近马达加斯加特有属Ornichia。Exacum属在这个部落中表现为最衍生的分类单元。系统发育树的拓扑结构与关于Exaceae生物地理学的冈瓦纳间断分布假说相符。然而，各种分歧时间分析都无法证实将该科内更古老的关系与构造历史相匹配的证据。分歧时间估计龙胆科在冈瓦纳大陆解体后约5000万年前（MYA）发生分化，而Exaceae部落约在4000万年前分化。莫桑比克海峡陆桥可能在Exaceae部落的生物地理历史中发挥了重要作用。
