Abstract:

    1.  Based upon the analyses in the floristic elements of the three genera (Suaeda,

Salsola and Zygophyllum) in different regions we can see that the genesis of our desert

floras in these regions is very much diversified.  The flora of Songaria is similar to that

of the Middle Asia, while the Hosi Corridor seems to be a transitional area very close to

Alashan and also related to the Tarim Basin in floristic elements. Thus, we may classify

the desert floras into three parts: the flora of Songaria, of Alashan including the Hosi

Corridor and of the Tarim Basin including the Tsaidam Basin. The ages and approa-

ches in their formation are different.

     2. There are plenty species but no or rare endemics in Songaria. In spring there

are a number of ephemeral plants. The variation of aspect is evident.  The vegetation

cover is abundant. The floristic elements are developed from the flora of Middle Asia

and it was formed in Quaternary period.

     3. The floristic elements of the Tarim Basin are poor, but there are not few en-

demics and the distribution of the endemics is much limited.  They are of the charac-

teristics of relic species.  Therefore it was formed in the Tertiary period and developed

in Quaternary period.  The elements are related to the Mediterranean flora.

     4.  There are a large number of endemics and many endemic monotypie genera in

Alashan.  They represent the flora formed in Tertiary period. Although it is of a special

style, it relates both to the Middle-Asian and the Mediterranean flora.

     5. The historic causes for the formation of the different floras lie chiefly on: (1)

The rise of the Tibetan plateau and mountains strongly changed the climatic and edaphic

conditions and in the long course of evolution some species survived or even developed,

while the others deteriorated or even died out from the flora. (2) Because the circum-

stances of transgression or regression of the Tethys were different in these regions. (3)

The mountain-making movement, the transgression and regression and the fluence of

glaciation, all the mutation of these associated factors modified the climatic zonation and

then the plant species changes followed, new species formed and migration of floristie

elements occurred. (4) Songaria is the nearest region to the then Sibirian glacier, so the

frozen injury to the flora might be the greatest. (5) In the Glacial period the descension

of snow line in Songaria was greater than that of the Tarim Basin, so the frozen injury

might be greater.