INTRODUCTION The family Fabaceae (Leguminosae) is by far the most diverse and widespread group of plants that have the capacity to host N-fixing baceteria. Ranking behind only the Asteraceae and Orchidaceae in size, the Fabaceae is the third largest family of flowering plants with about 650 genera and 18,000 species (Sprent, 1995; Akran et al., 2009). The Fabaceae is broken up into sub-families: the Caesalpiniodeae, the Mimosoideae and the Papilioniodeae (Sprent, 1995). The Caesalpiniodeae and Mimosoidae mainly consist of woody shrubs and trees that are largely confined to tropical and subtropical regions. The Papilionoideae is made up of woody shrubs and trees as well as perennial and annual herbs; this sub-family is distributed worldwide with the woody members being largely concentrated in the tropics and sub-tropics (Kass et al., 1997; Al-Taweil et al., 2009).