As part of an assessment of the vascular plant families endemic to Madagascar and the Comoro Islands, a synoptic revision is presented of Sphaerosepalaceae, comprising two genera, Dialyceras (3 spp.) and Rhopalocarpus (15 spp.). Molecular sequence data suggest the family's relationship to Bixaceae and Cochlospermaceae (and also perhaps to the Malagasy endemic Diegodendron) in an expanded Malvales. Critical study of available herbarium material shows the diagnostic value of vegetative characters for delimiting species, especially within Rhopalocarpus, in which two new combinations are made and five formerly recognized taxa are placed in synonymy. All but five members of the family occur in the humid and subhumid forests of eastern Madagascar, especially around the Bay of Antongil and on the Masoala Peninsula, where all three Dialyceras and eight Rhopalocarpus have been recorded. Keys to the genera and species are provided in English and French.
Sphaerosepalaceae, Dialyceras, Rhopalocarpus, Madagascar, endemism