Some sources include this genus with the heather voles, genus "Phenacomys". The genus Phenacomys is a group of North American voles. The eastern heather vole, ("Phenacomys ungava"), is a small North American vole. The western heather vole ("Phenacomys intermedius") is a small vole found in western North America. Until recently, the eastern heather vole, ("Phenacomys ungava"), was considered to be a subspecies. During the Ice Ages of the Pleistocene, "Phenacomys" voles lived as far south as Arkansas.