Phylogenetic relationships between disjunctly occurring groups of Tristicha trifaria (Podostemaceae)
To reveal the phylogeographic relationship of disjunct specimens of Tristicha trifaria (Bory ex Willd.) Spreng., a member of the Podostemaceae river-weed family, which is distributed exceptionally widely, but disjunctly, in Africa and the Americas. Location
Brazil, Mexico, Ghana, Tanzania and Madagascar. Methods
The chloroplast matK and rbcL genes, a trnK intron, the trnS-trnG intergenic spacer (IGS), the two IGSs of trnT-trnL-trnF, a trnL intron, and nuclear ribosomal ITS regions were sequenced and analysed. Phylogenetic analyses were conducted using maximum likelihood and maximum parsimony methods. Results
The T. trifaria samples analysed were separated into two groups in a rooted tree based on a combined matK/rbcL/ITS dataset; one contained the West African and all of the American samples, and the other contained the East African and Madagascan samples. An unrooted tree obtained from a combined analysis of all the chloroplast DNA and nuclear ITS data showed that a sample from West Africa was sister to an American T. trifaria group. Main conclusions
The American and West African T. trifaria are closely related, despite the great distance between their locations. This observation, along with a tree of the whole Tristichoideae subfamily and estimated divergence times, suggests that an ancestor of T. trifaria migrated from Asia to Africa during the early Tertiary, and that this was followed by further westward migration to the Americas at the end of the Miocene or in the early Pliocene.