Between Cancer and Capricorn: Phylogeny, evolution and ecology of the primarily tropical Zingiberales

The Zingiberales are a group of primarily tropical monocots that includes eight families, ca. 96 genera, and about 2,000 species. Phylogenetic results based on sequence data and morphology show that the four "banana-families" (Musaceae, Lowiaceae, Strelitziaceae, and Heliconiaceae) share the plesiomorphic state of five or six fertile stamens and comprise a basal paraphyletic assemblage. The four "ginger-families," with the synapomorphy of a single fertile anther and four or five highly modified staminodia, form a terminal clade of two lineages with the Zingiberaceae + Costaceae and Cannaceae + Marantaceae as sister groups. The Zingiberales are found on all major continents with tropical climates. While Marantaceae, Zingiberaceae, and Costaceae are pantropically distributed, Musaceae is found only in Southeast Asia and Africa, Strelitziaceae only in Africa and the Americas, and Heliconiaceae only in the Americas and Melanesia. The two families most restricted in distribution, Lowiaceae and Cannaceae, are found only in Southeast Asia or the Americas, respectively. The historical biogeography of the family was reconstructed using dispersal-vicariance analysis in combination with dating of nodes based on evidence from the fossil record and local molecular clocks rising atpB sequence data. The common ancestor of the Zingiberales is estimated to have originated 158 Ma with six of the eight families established by the end of the Cretaceous. Dispersal-vicariance analyses suggest that the ancestral Zingiberales were distributed in tropical Gondwanaland encompassing the present day Americas, Africa, and Southeast Asia with subsequent dispersals between Africa and the Americas. The current distribution of the Zingiberales is a product of numerous secondary and tertiary dispersal events between the major tropical regions of the world. The phylogenetic diversification and biogeographic dispersal of the Zingiberales was in part driven by the evolutionary radiation and diversification of their associated animal pollinators, which include bats, birds, non-flying mammals, and insects. Six of the eight families of the Zingiberales contain taxa specialized for pollination by vertebrates, which appears to be the plesiomorphic state in the order. Of these six families two are exclusively vertebrate-pollinated (Strelitziaceae, Heliconiaceae). Pollination by insects also occurs in six families with one (Marantaceae) or possibly two (Lowiaceae) families predominantly specialized for insect visitors. Current models of the genetic regulation of floral development coupled with phylogenetic data and ecological observations provide new insights into the evolutionary pathways that have resulted in the wonderful diversity of this widespread order of tropical angiosperms.