The diademed sifaka is one of the mostly widely distributed member of the genus "Propithecus", although definitive mapping of its range has not been conducted. Occurrence is at altitudes of 200 to 800 metres (656 to 2,624 feet) throughout much of the eastern Madagascar lowland forests and altitudes 800 to 1,550 metres (2,624 to 5,084 feet); in portions of the Madagascar subhumid forests. These two biomes have been designated as a Global 200 ecoregion, one of the world's most significant regions for conservation. Geographically the range extends to at least the Mananara River in the north to the Onive and Mongoro Rivers in the south. One set of researchers has recorded a clinal variation between "Propithecus diadema" and "Propithecus edwardsi" in the extreme southern portion of the range. As with all Indriidae, this species and its entire genus have evolved on the island of Madagascar independent of other mainland African species.