Which is a genus native to more areas of the world, Ailanthus or Leonotis? 
Ailanthus:  The genus is native from east Asia south to northern Australasia. Leonotis:  One species, "Leonotis nepetifolia", is native to tropical Africa and southern India. Leonotis:  It is naturalized throughout most of the tropics. Leonotis:  The other species are endemic to southern + eastern Africa.
Leonotis