Phylogenetic relationships in the commelinaceae: I. A cladistic analysis of morphological data

The plant family Commelinaceae displays a wide range of variation in vegeta tive, floral, and inflorescence morphology. This high degree of variation, particularly among characters operating under strong and similar selective pressures (i.e., flowers), has made the assessment of homology among morpho logical characters difficult, and has resulted in several discordant classi fication schemes for the family. Phylogenetic relationships among 40 of the 41 genera in the family were evaluated using cladistic analyses of morphol ogical data. The resulting phylogeny shows some similarity to the most rece nt classification, but with some notable differences. Cartonema (subfamily Cartonematoideae) was placed basal to the rest of the family. Triceratella (subfamily Cartonematoideae), however, was placed among genera within tribe Tradescantieae of subfamily Commelinoideae. Likewise, the circumscriptions of tribes Commelineae and Tradescantieae were in disagreement with the mos t recent classification. The discordance between the phylogeny and the most recent classification is attributed to a high degree of convergence in var ious morphological characters, particularly those relating to the androeciu m and the inflorescence. Anatomical characters (i.e., stomatal structure), on the other hand, show promise for resolving phylogenetic relationships wi thin the Commelinaceae, based upon their agreement with the most recent cla ssification.