Mayflies (Ephemeroptera) are a merolimnic insect order (part of the life cycle is aquatic) and play an important role as biological indicators of river ecosystem health. In the Afrotropical realm (including sub-Saharan Africa and Madagascar), this order presently encompasses 122 genera and more than 400 species; all species and 85% of the genera are endemic to the Afrotropics. A great part of the diversity still remains unknown. The specific and generic diversity of mayfly families from Madagascar and from 4 sub-Saharan African subregions (West Africa, western Central Africa, eastern Central Africa, and southern Africa) is presented. A concurrent comparison of this diversity with the level of taxonomic knowledge for each subregion highlights inadequacy of knowledge. It is important for freshwater conservation biologists and ecologists, and for biomonitoring programs, to have a level of certainty when identifying taxa. This preliminary synthesis is intended to stimulate future taxonomic research and collecting efforts in understudied regions that will lead to species descriptions and recognition of the biodiversity of these regions. This information will feed into regional identification keys and enable more accurate species identification. Greater understanding of the diversity of organisms, the foundation for all ecological studies, can be used to refine biomonitoring protocols for freshwater organisms.