A phylogeny and biogeographic analysis for the Cape-Pondweed family Aponogetonaceae (Alismatales)

The monocot family Aponogetonaceae (Alismatales) consists only of Aponogeton, with 57 species occurring in Africa, Madagascar, India and Sri Lanka, Southeast Asia and Australia. Earlier studies inferred a Madagascan or Australian origin for the genus. Aponogeton-like pollen is documented from the Late Cretaceous of Wyoming, the early mid-Eocene of Canada, and the late mid-Eocene of Greenland. We obtained nuclear and plastid DNA sequences for 42 species and generated a time-calibrated phylogeny, rooted on appropriate outgroups. Statistical biogeographic analyses were carried out with or without the fossils incorporated in the phylogeny. The recent-most common ancestor of living Aponogetonaceae appears to date to the mid-Eocene and to have lived in Madagascar or Africa (but not Australia). Three transoceanic dispersal events from Africa/Madagascar to Asia sometime during the Miocene could explain the observed species relationships. As inferred in earlier studies, an ancient Australian species is sister to all other Aponogetonaceae, while the remaining Australian species stem from an Asian ancestor that arrived about 5. million years ago. The family's ancient Northern Hemisphere fossil record and deepest extant divergence between a single Australian species and an Africa/Madagascar clade are statistically well-supported and rank among the most unusual patters in the biogeography of flowering plants.