15 species) Tsutsusi (Sweet) Pojarkova (65 species) Subgenus Azaleastrum Planch. (2 sections, 16 species) (Increased to three sections) Azaleastrum Planch. (5 species) (Choniastrum Franch. (11 species) (Raised to subgenus)) (Sciadorhodion Rehder & Wilson (4 species) (Moved from subgenus Pentanthera)) (Tsutsusi (Sweet) Pojarkova (reduced from subgenus)) Subgenus Candidastrum Franch. (1 species: Rhododendron albiflorum) (Discontinued, moved to section Sciadorhodion, subgenus Azaleastrum) Subgenus Mumeazalea (Sleumer) W.R. Philipson & M.N. Philipson (1 species: Rhododendron semibarbatum) (Discontinued, moved to section Tsutsusi, subgenus Azaleastrum) Subgenus Therorhodion A. Gray (2 species) (Subgenus Choniastrum Franch. (11 species)) Distribution and habitat Species of the genus Rhododendron are widely distributed between latitudes 80°N and 20°S and are native to areas from North America to Europe, Russia, and Asia, and from Greenland to Queensland, Australia and the Solomon Islands. The centres of diversity are in the Himalayas and Malaysia, with the greatest species diversity in the Sino-Himalayan region, Southwest China and northern Burma, from India – Himachal Pradesh, Uttarakhand, Sikkim and Nagaland to Nepal, northwestern Yunnan and western Sichuan and southeastern Tibet. Other significant areas of diversity are in the mountains of Korea, Japan and Taiwan. More than 90% of Rhododendron sensu Chamberlain belong to the Asian subgenera Rhododendron, Hymenanthes and section Tsutsusi. Of the first two of these, the species are predominantly found in the area of the Himalayas and Southwest China (Sino-Himalayan Region). The 300 tropical species within the Vireya section of subgenus Rhododendron occupy the Malay archipelago from their presumed Southeast Asian origin to Northern Australia, with 55 known species in Borneo and 164 in New Guinea. The species in New Guinea are native to subalpine moist grasslands at around 3,000 metres above sea level in the Central Highlands. Subgenera Rhododendron and Hymenanthes, together with section Pentanthera of subgenus Pentanthera are also represented to a lesser degree in the Mountainous areas of North America and Western Eurasia. Subgenus Tsutsusi is found in the maritime regions of East Asia (Japan, Korea, Taiwan, East China), but not in North America or Eurasia. In the United States, native Rhododendron mostly occur in lowland and montane forests in the Pacific Northwest, California, the Northeast, and the Appalachian Mountains. Ecology Invasive species Rhododendron ponticum has become invasive in Ireland and the United Kingdom. It is an introduced species, spreading in woodland areas and replacing the natural understory. R. ponticum is difficult to eradicate, as its roots can make new shoots. Insects A number