A phylogenetic analysis of the Commelinaceae based on morphological and molecular data

The Commelinaceae is a well defined family of 40 genera and about 650 species. Due to the extensive morphological variation within the family, intrafamilial relationships have been problematic. Characters that may be useful for evaluating relationships among one group of genera may be either missing or convergent among other genera. Additionally, assessment of homology of various characters, particularly structures in the inflorescence, is difficult at best, making strictly morphologically based classifications of the family suspect. Relationships among the genera of Commelinaceae were evaluated using phylogenetic analyses of: (1) floral, vegetative, and anatomical characters; and (2) nucleotide sequence data from the chloroplast encoded gene rbcL. Cladistic analysis of each data set revealed substantial incongruency between morphological and molecular phylogenies. The molecular phylogeny is more consistent with the most recent classification of the family than is the morphological phylogeny. The family is monophyletic, with the morphologically distinct genus Cartonema (at times placed into its own family, Cartonemataceae) basal. Two large clades were found, corresponding roughly to the subtribes Tradescantieae and Commelineae sensu Faden and Hunt. Additional methods of analysis of the molecular data (neighbor-joining and maximum likelihood) are in general agreement with the cladistic analysis. Incongruency within and between the data sets was examined through consensus techniques and through analysis of combined data sets. Approximately one third of the total incongruency was attributed to disagreement between the morphological and molecular data, while two thirds of the incongruency was attributed to within-data set conflict. Consensus provided little phylogenetic information, whereas the "total data" approach yielded increased phylogenetic resolution.