|Title||Molecular systematics of tribe Rubieae (Rubiaceae): evolution of major clades, development of leaf-like whorls, and biogeography|
|Publication Type||Journal Article|
|Year of Publication||2010|
|Authors||Soza VL, Stirling B, Olmstead RG, Bingham J-P|
Rubieae are centered in temperate regions and characterized by whorls of leaf-like structures on their stems. Previous studies that primarily included Old World taxa identified seven major clades with no resolution between and within clades. In this study, a molecular phylogeny of the tribe, based on three chloroplast regions (rpoB-trnC, trnC-psbM, trnL-trnF-ndhJ) from 126 Old and New World taxa, is estimated using parsimony and Bayesian analyses. Seven major clades are strongly supported within the tribe, confirming previous studies. Relationships within and between these seven major clades are also strongly supported. In addition, the position of Callipeltis, a previously unsampled genus, is identified. The resulting phylogeny is used to examine geographic distribution patterns and evolution of leaf-like whorls in the tribe. An Old World origin of the tribe is inferred from parsimony and likelihood ancestral state reconstructions. At least eight subsequent dispersal events into North America occurred from Old World ancestors. From one of these dispersal events, a radiation into North America, followed by subsequent diversification in South America, occurred. Parsimony and likelihood ancestral state reconstructions infer the ancestral whorl morphology of the tribe as composed of six organs. Whorls composed of four organs are derived from whorls with six or more organs. Transitions between four and six or more organs per whorl are common within the tribe, whereas reduction to two leaves at a node is derived and rare.
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Molecular systematics of tribe Rubieae (Rubiaceae): evolution of major clades, development of leaf-like whorls, and biogeography
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