Phylogenetic Relationships in the Commelinaceae: I. A. Cladistic Analysis of Morphological Data

The plant family Commelinaceae displays a wide range of variation in vegetative, 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 morphological characters difficult, and has resulted in several discordant classification schemes for the family. Phylogenetic relationships among 40 of the 41 genera in the family were evaluated using cladistic analyses of morphological data. The resulting phylogeny shows some similarity to the most recent classification, but with some notable differences. Cartonemna (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 oftribes Commelineae and Tradescantieae were in disagreement with the most recent classification. The discordance between the phylogeny and the most recent classification is attributed to a high degree of convergence in various morphological characters, particularly those relating to the androecium and the inflorescence. Anatomical characters (i.e., stomatal structure), on the other hand, show promise for resolving phylogenetic relationships within the Commelinaceae, based upon their agreement with the most recent classification. The Commelinaceae, a well defined family of 41 genera and about 650 species, is characterized by several features including a distinct closed leaf sheath, a succulent leaf blade, and three-merous flowers with distinct petals and sepals (Cronquist 1981; Faden 1985; Faden and Hunt 1991). The genera are largely tropical and subtropical, but several extend into temperate regions. The greatest diversity is in Africa, where, along with Madagascar, nearly half the genera and about 40% of the species are found (Faden 1983a). There is a natural division of taxa between the Old and the New World. The seven subtribes of tribe Tradescantieae (sensu Faden and Hunt 1991) are each wholly confined to either the Eastern or Western hemisphere, whereas the tribe Commelineae is found mainly in Africa and Asia. Only six genera (Aneilema, Buforrestia, Commelina, Floscopa, Murdannia, and Pollia) have indigenous species in