The Singalila Range, forming the political boundary between Sikkim and Nepal, springs from Khangchendzonga and extends southwards to the plans of Bengal. The super abundance of rhododendrons is the glory of the Singalila Range. The banks of rivers between 8000 and 14000 feet are generally covered with rhododendrons sometimes to the total exclusion of other wooded vegetation, especially near the snowy mountain, a cool temperature and great humidity being the most favourable conditions for the luxurious growth of this genus.
(Hooker's Himalayan Journal)
Rhododendron arboreum, Smith - introduced UK about 1810
Rhododendron cinnabarinum, Hooker fil. - introduced 1849
Rhododendron falconeri, Hooker fil. - introduced about 1830
Rhododendron barbatum, Wallich - introduced about 1849
Rhododendron campanulatum, Don. - introduced 1825 (Bot. Mag., t. 3759)
Rhododendron hodgsoni Hooker fil. - introduced 1849 (Bot. Mag., t. 5552)