PHYLOGENETIC IMPLICATIONS OF RBCL SEQUENCE VARIATION IN THE ASTERACEAE

Complete nucleotide sequences of the rbcL gene were obtained for 25 species of Asteraceae representing 15 of the currently recognized tribes and three outgroup families. A total of 345 variable nucleotide positions was identified, 170 of which were phylogenetically informative. Phylogenetic analyses of the rbcL data generated eight equally parsimonious trees with a consistency index of 0.47. Three major monophyletic clades that correspond to the subfamilies Barnadesioideae, Cichorioideae, and Asteroideae were identified in the most parsimonious cladograms; however, support for these groups was not strong. Relationships among tribes were not supported strongly except for the close affinity of the Tageteae, Coreopsideae, Heliantheae, and Eupatorieae. These results are congruent with chloroplast DNA restriction site comparisons with respect to the subfamilial circumscription in the Asteraceae and the sister group relationship of the Heliantheae and Eupatorieae. In contrast, morphological cladograms indicated the paraphyly of the Cichorioideae and a closer relationship of the Eupatorieae to the Astereae. Parsimony analyses were also performed on data sets combining rbcL and cpDNA restriction site mutations and DNA and morphological characters. These phylogenies provide moderate to strong support for the monophyly of the Asteroideae and Cichorioideae and the sister-group relationship of the Eupatorieae and Heliantheae. Comparisons of trees generated from restriction site and sequence data also indicate that cpDNA restriction site data from the entire chloroplast genome are more useful for phylogenetic studies in the Asteraceae than sequences from the highly conserved rbcL gene. This is due to the sampling of more sequence variation in the restriction site comparisons and the higher incidence of homoplasy in the sequence data.