Phylogeny of the tribe Colletieae (Rhamnaceae) -: a sensitivity analysis of the plastid region trnL-trnF combined with morphology

The phylogenetic relationships within the tribe Colletieae (Rhamnaceae) were examined combining data from a previous morphological analysis with data from the trnL intron and trnL-F spacer. Previous studies have failed to confirm monophyly of the genus Discaria, the only genus of the tribe with an amphiantarctic distribution. The data set was analyzed using direct optimization as implemented in the computer program POY. Direct optimization searches for multiple optimal sequence alignments and is therefore well suited for analyzing DNA sequences including ambiguous alignable regions as found in the present study. Eight different costs were used for treating the indel information. Indels were treated as single events, equal to a fifth character state, or strings of gaps were treated as single events using different costs for opening a gap and extending the gap. The optimal cost set was selected by use of both character-based and topological congruence measures. Both congruence measures agreed upon a single optimal cost set. The resulting tree generally agrees with the current taxonomic treatment of the tribe Colletieae that recognizes six genera out of which three are monotypic. However, monophyly of Discaria was not supported and the results strongly suggest segregating D. nana and D. trinervis, and re-establishing the genus Ochetophila.