UC Berkeley

Recent cladistic analysis Of Multiple molecular data from chloroplast and nuclear genomes as well as morphological data have indicated that a reclassification of the family Costaceae is necessary in order to appropriately reflect phylogenetic relationships. The previously described genera Tapeinochilos, Monocostus, and Dimerocostus are all upheld in the new classification. Monocostus and Dimerocostus are found to be sister taxa. The large pantropical genus Costus is found to be polyphyletic and is thus divided into four genera, three of which are new (Cheilocostus, Chamaecostus, Paracostus). Costus has now a more concise generic concept including morphological synapomorphies previously absent due to the polymorphic nature of the prior nonmonophyletic assemblage. Of the three new genera, one (Parocostus) was previously recognized as a subgenus of Costus. Cheilocostus comprises several Asian taxa and is sister to Tapeinochilos, whereas Chamaecostus comprises entirely neotropical taxa and is sister to a neotropical Monocostus + Dimerocostus clade. A reevaluation of the traditional taxonomy indicates that floral characters and pollination syndromes commonly used to identify groups exhibit homoplasy when analyzed in a cladistic framework and are thus unreliable as taxonomic indicators.