1. Department of Biology, Umaru Musa Yar’adua University , P.M.B. 2218, Katsina , Nigeria
2. Department of Molecular Evolution and Plant Systematics & Herbarium (LZ), Institute of Biology, Leipzig University , Johannisallee 21–23, D-04103 Leipzig , Germany
3. German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig , Puschstraße 4, D-04103 Leipzig , Germany
4. Department of Paleobiology, National Museum of Natural History, Smithsonian Institution , Washington, DC , USA
5. Department of Geography, Environmental Management and Energy Studies, University of Johannesburg , Auckland Park 2006, Johannesburg , South Africa