Systematics of Ipomoea subgenus Quamoclit (Convolvulaceae) based on ITS sequence data and a Bayesian phylogenetic analysis†

A Bayesian phylogenetic analysis of 36 Ipomoea species using sequence data from the internal transcribed spacer region was compared with classification schemes based on traditional methods and a previously published cpDNA restriction fragment length polymorphism (RFLP) study. These molecular studies support a diversity of groups that were circumscribed on the basis of phenetic principles and agree generally with the results from cpDNA RFLP analyses. The congruence between the phylogenetic hypotheses based on new molecular data and the understanding of relationships developed in earlier studies indicate that these classifications may reflect evolutionary history. Two large clades of species, with one including sections Tricolores, Calonyction, and Pharbitis and the other including sections Mina and Leptocallis, were identified. Furthermore, morphologically distinct groups of Ipomoea species received support from the DNA sequence data. Indices of convergence for the Markov chain Monte Carlo (MCMC) in the Bayesian phylogenetic analysis were evaluated. A limited range of posterior probabilities for each node in the trees from a set of five MCMC samples provides a useful index of convergence. Bayesian node support values were generally higher than bootstrap values from a maximum parsimony analysis. This is consistent with the notion that these measures of support estimate different qualities of the data