A phylogenetic study was conducted on a group of three small genera of neotropical Commelinaceae that exhibit a variety of unusual floral morphologies and habits. Morphological characters and DNA sequence data from plastid (rbcL, trnL-F) and nuclear ribosomal (5S-NTS, partial 26S) loci were used. In separate analyses, 26S and rbcL character sets each yielded cladograms that were equally or more fully resolved than those from analyses of the more rapidly-evolving 5S-NTS and trnL-F loci. Analysis of the molecular character sets, in combination with morphological characters, has provided a framework for the study of life form and morphological character evolution. Our studies indicate that the unusual spirally-coiled anthers and other apparent autapomorphies in the flowers of Cochliostema are elaborations of developmental synapomorphies shared by Cochliostema with Geogenanthus and an undescribed genus. The adaptations associated with the epiphytic habit of Cochliostema are best understood in light of their similarity to homologous features in the undescribed genus. Our inclusion in this study of two undescribed plesiomorphic species of Geogenanthus has revealed an evolutionary trend towards reduction in the inflorescence in this genus.

Key words: Cochliostema, Commelinaceae, Geogenanthus, ribosomal DNA