H. grandis has a very restricted range, only four specimens having been gathered from a single location at above sea level on the slopes of Mount Oku in Cameroon. Its total area of occurrence is approximately and little of the natural forest in which it lives remains, as trees are being felled to make way for agriculture, and to provide timber for construction and firewood. Because of these factors, the International Union for Conservation of Nature has rated its conservation status as being endangered.