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A phylogenetic analysis of molecular (ITS, trnL-F trnK including the matK coding region) and morphological data is presented for the pantropical monocot family Costaceae (Zingiberales), including 65 Costaceae taxa and two species of the outgroup genus Siphonochilus (Zingiberaceae). Taxon sampling included all four currently described genera in order to test the monophyly of previously proposed taxonomic groups. Sampling was further designed to encompass geographical and morphological diversity of the family to identify trends in biogeographic patterns and morphological character evolution. Phylogenetic analysis of the combined data reveals three major clades with discrete biogeographic distribution: (1) South American, (2) Asian, and (3) African-neotropical. The nominal genus Costus is not monophyletic and its species are found in all three major clades. The Melanesian genus Tapeinochilos is monophyletic and included within the Asian clade. Monocostus and Dimerocostus are sister taxa and form part of the South American clade. The African-neotropical clade is composed entirely of the genus Costus; moreover, there is support for previously recognized subgeneric groupings within the Costus clade. Evolutionary trends in floral morphology show that close associations with pollinators have evolved several times from an ancestral generalist pollinator floral form. Bee pollination has evolved once in the family, arising in Africa from an open-flowered (generalist) ancestor. Bird pollination has evolved multiple times: once from an open-flowered ancestor in Southeast Asia and multiple times from a bee-pollinated ancestor in the neotropics. Additional morphological characters not traditionally used to define taxonomic groups, but having high consistency in the current phylogenetic analysis, are discussed.
Chelsea D. Specht (2006) studied this question.