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Abstract
Ipomoea aquatica, a vegetable cultivated and used medicinally in Asia and Africa, can become a noxious invasive weed on water and land, making navigation difficult, and displacing native species. Ecogeographic, morphological and cytological studies of the species revealed two established perennials, widely distributed and savanna-restricted ecotypes, and a sporadic annual forest type. The seeds of the annual germinated in soil after 6–8 weeks with smaller cotyledons while the perennial germinated within 2 (6) weeks with slightly larger cotyledons. They were distinguished into narrow and broad leaf morphotypes with variable leaf shapes. The wetland perennials reproduced largely by vegetative means, producing one to three flowers per inflorescence with fewer but larger fruits and seeds modified for water dispersal. The upland annual reproduced by seeds, producing 4–10 flowers per inflorescence with many but smaller fruits and dormant seeds adapted to dry conditions. The chromosome number (2n) was 30 and 28 for the perennial and annual biotypes, respectively. The mechanisms involved in the evolution of the species, its variability and spread are discussed.
Acknowledgements
We thank the council of the University of Lagos for providing research assistantship grants (AD/REG/4397 & 4411) for travels and field studies in Nigeria. Profound appreciation to Dr Susan Scharffenberg, Dean of the Faculty of Science, Mission College, Muak Lek, Thailand for facilitating teaching and travel grants to the senior author for a trip to Thailand in 2002. Our gratitude to the Academy of Sciences for the Developing World (TWAS), Italy, UNESCO and the Brazilian Research Council (CNPq) for providing research and travel grants to the senior author for visits to Brazil in 2006 and 2007. We are indebted to Late Prof. R.E. Ugborogho FLS for support and useful suggestions in the course of the study. Dr Roy Vickery, Dr Charlie Jarvis, Ms Gina Douglas, Dr Olof Ryding and Rusty Russell, curators, librarian/archivist and collection manager at NHM, LINN-England, C-Denmark and USNH-USA, who granted the use of their herbaria, libraries and/or materials with technical support. Acknowledgements are also due to the curators and staff of FHI, IFE, LUH, UIH and UNH, Nigeria. Mr Issa Ibraheem of the Cell Biology and Genetics Department, University of Lagos painstakingly printed the photographs. Logistic support from Mr Larry Ogunwenmo for visits to USNH, NHM and LINN, and acquisition of relevant materials is highly appreciated.