The two clades correspond to a geographical separation, the main distributions being divided by the section of the Brahmaputra River which flows south at the end of the Himalayan mountain chain. Historical biogeography study revealed that evolutionary split between Cautleya and Roscoea occurred during the middle and late Eocene to the early Oligocene, corresponding well to the proposed early uplift of the Himalayas and Qinghai-Tibetan Plateau. Roscoea species were then divided into two distinct clades, simultaneous with the rapid extrusion of Indochina and accompanied by the another Himalayan uplift around the Oligocene/Miocene boundary. It has been suggested that the genus may have originated in this area and then spread westwards along the Himalayas and eastwards into the mountains of China and its southern neighbours, supported by biogeographic reconstruction. Three species have an isolated distribution. R. brandisii, a member of the Himalayan clade, occurs to the south of the rest of the clade in the Khasia Hills in the modern Indian state of Meghalaya (formerly part of the state of Assam). R. australis, a member of the Chinese clade, occurs even further south, in the Chin Hills of Burma. R. ngainoi, discovered after the phylogenetic analysis discussed above, is found roughly between these two species, in the Indian state of Manipur.