From Sir J. D. Hooker’s Diary

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. Such conditions prevailing throughout the Singalila range due to its proximity with the Khangchendzonga range. The Nepal frontier road terminates at the staging bungalow of Chewabhanjan, and from thence the only path available for marching is the sheep path running onwards to the grazing grounds which lie towards Jongri. The only large trees existing in the country traveled over are Abies densa, Juniperus pseudo-Sabina, and Juniperus recurva. The silver fir extends to 13,000 feet, the junipers to 15,000 feet. Where the former is only a small, stunted, weather worn tree, the other, a prostrate, intricately branched shrub. For many miles the path runs through woods of Rhododendron arboreum, Rhododendron cinnabarinum, Rhododendron falconeri, Rhododendron barbatum, Rhododendron campanulatum, and Rhododendron hodgsoni, Acer caudatum, Betula utilis, Pieris ovalifolia, Prunus rufa, Pyrus foliolosa, P. macrophylla etc. Here also are seen the last examples of the bamboo tribe, Arundinaria spathiflora and A. racemosa, a small variety not exceeding a height of three feet. The upper limit of these bamboos is 13,000 feet, from thence upwards only small tufted species of grasses abound. The shrubby vegetation already enumerated grows so densely that few herbaceous plants can exist beneath it. Beautifully green moss carpets the boulders, an Saxifraga ligulata, Potentilla, Clintonia, Polygonum, and two species of ferns are the commonest plants. On open knolls which occur but rarely, Gaultheria nummularia, small willows, and the heather like Cassiope fastigata cover the ground with their dense growths. Towards the termination of the range rhododendrons and other shrubs grow sparsely, thus favouring the existence of a greater variety of herbaceous plants, primroses become more abundant, the prevalent species being the water loving Primula sikkimensis and Primula reticulata, and also those growing on dry ground, such as Primula stuartii and Primula denticulata.