Richness, similarity and specificity of Madagascar flora compared with Sub-Saharan Africa

Background and aims - Based on presence/absence information for all angiosperms in Tropical Africa, Southern Africa and Madagascar, we review the similarities and differences between these floras. We compare specific and generic richness for the three areas, and examine their degree of overlap. Madagascar and Sub-Saharan Africa are compared in terms of: the specific and generic richness of their angiosperm families, and specific richness of their genera. Methods - Using the African Plant Database, global figures of specific and generic richness for Tropical Africa, Southern Africa and Madagascar have been calculated and illustrated by Venn diagrams. For each family or genus similarity between Sub-Saharan Africa and Madagascar has been calculated using the Jaccard Index. Madagascar specificity has been defined as the ratio of Madagascar-exclusive species richness to total richness. Key results - The study confirms the general trends of richness and endemism in the Malagasy flora, but provides accurate figures based on the current state of angiosperm taxonomy. Overlap between the floras of Southern African, Tropical African and Madagascar flora is provided with precise figures. Similarity between Madagascar and Sub-Saharan Africa is very low at species level (0.029) and eight times higher at generic level (0.246). Madagascar specificity reaches 0.165 at specific level and 0.105 at generic level. Calculation of these two indexes for families and genera, based for the first time on APG III, confirms general trends observed so far, and the richest families of the Malagasy flora are listed according to major patterns of their diversity and distribution.