Introduction

Southern Africa, which is the region south of the Rivers Cunene and Zambezi, is one of the world’s bee diversity hotspots (Kuhlmann 2009). As bees are the most important pollinators of flowering plants, including crops, they are ecological and economic keystone species (Corbet et al. 1991; Allen-Wardell et al. 1998; Klein et al. 2007). Pollinators are believed to have played an important role in plant speciation in southern Africa, especially in the Cape Floral Kingdom (Kreft and Jetz 2007; van der Niet and Johnson 2008; Waterman et al. 2008). Notwithstanding the great economic, ecological, and evolutionary significance of wild bees, knowledge of this important group of pollinators and their floral relationships in this region is poor.

Struck (1990, 1994a, 1994b, 1995) was the first to extensively study the relationships between flowers and solitary bees in southern Africa. In his pioneering work in Namaqualand, he used pollen analyses for recording flower visitation to investigate flower specialization of bees and other flower visiting insects. But due to taxonomic uncertainties in many of the bee genera in those days, the published data is of limited usefulness without the re-examination of the specimens, and thus it is not considered here.