DISTRIBUTION OF FLORAS IN S. E. ASIA. 25
many alpines such as Polygonum Forsterii, Primula serratifolia, Cassiope palpebrata, besides sub-alpines such as Primula sonchi folia, Nomocharis, etc.
But with the flora of Yunnan east of the Salween, apart from the high ranges which thrust long processes southwards from the north- ern mountain masses, the North Bast Frontier flora seems to have nothing in common.
Endemic species are found especially in the alpine region, and to a lesser extent at intermediate altitudes. Amongst the former may be mentioned species of Rhododendron, Primula, Cremanthodinm etc., amongst the latter the monotypic genera Becsia and Sporoxia, species of Strobilanthes, Codonopsis and various Gesnerads.
Those plants which are both Himalayan and Chinese are widely distributed across eastern Asia, often occurring in Japan as well and sometimes even in N. America, (e.g., Clitoria mariana). On the other hand there are plants ranging from the Himalaya into western China, which are not found on the N. E. Frontier, (e.g., Isopyrum grandiflorum).
Plants from what I have called the Burma-Yunnan area are not found in the Himalaya. This area is simply the splayed out ends of the North East Frontier belt, tailing off southwards into the Indo- Malayan region; it has carried this flora southwards into the Indies, where for instanco Primula imperially is found on the mountains of Java.
But many plants of the Himalayan foot hills, representing the Indo-Malayan element, are found in the Burma-Yunnan area.
Negative results in the alpine belt are as valuable as positive results. I have insisted on the relationship of the alpine flora to that of the Himalaya and western China ; but what shall we say to the complete absence of such typical genera as Aquilegia, Tncarvillea, Primulas of the Amethystma section, and Pinguicula alpina ; and to the extreme poverty of such as Meconopsis, woolly Compositae, alpine Leguminosae, Berber is, Cotoneaster , Lonicera, etc.? In view of the large number of Rhododendrons, especially of the dwarf groups, we are, forced to the conclusion that if it is simply a question of altitude — and the highest peaks are little over 13,000 feet — then altitude affects plants both absolutely and relatively. In other words, Rhodadendrons flourish within 1,000 feet of the snow line, wherever the snow line may be ; but Meconopsis for instance, flourishes only above 15,000 feet.
We are now in a position to appreciate to some extent the part played by the North East Frontier belt as regards distribution in South East Asia generally.
