Studies On The Systematics Of Domestic Leymus And Plant Geography

Firstly, This paper studied the literature of Leymus, the arrangement and analysis were carried out; Then, we summarized the research history of Leymus; Finally We did some research about this genus by using morphology, anatomy, molecular systematics and phytogeography methods. According these data, the phylogenetic relationships of Leymus were analysed. Then combined with the geographical distribution of the genus, the distribution center, time and place of origin and formation of the modern distribution pattern of this genus were discussed. The main results were showed as follows:1. Morphological observation of the main character differences of 72 reprehensive populations from 24 Leymus species that previously reported by scholars were examined under light microscope. The result showed that there were different degrees of 15 morphological characters including length and width of flag leaves,hairs of leaf blades, straight or curve and length or width of inflorescence, spikelet No.of each inflorescence, floret No. of each spikelet, etc. Then the systematic evolution and some infrageneric relationship were discussed. At the same time, SPSS software was used under the principal component analysis of Leymus. The tested species were divided into 3 different groups that the sect. Racemosus group included 4 species, the sect. Leymus group included 17 species and the Anisopyrum group included 3 species;Meanwhile, The differences among different groups were compared and the phylogenetic relationship of Leymus was analysed.2. The leaf epidermis microscopic characteristics of 24 species were observed under Olympus microscope, which were found that the leaf epidermis of Leymus from China consists of long cell, stomatal cell, short cell and prickle hair among the 24 taxa of Leymus. It belongs to the typical festucoid type. in addition, the length of long-cells and curve extent of cell walls, distribution pattern of short-cells, shape of subsidiary cells, type of prickle-hairs, etc, which existed obvious differences. Then combined with the external morphological characters, the evolutionary relationships among them were discussed.3. Molecular phylogenetic tree was reconstructed. We used ITS sequence, rbcLsequences, trnH-psbA sequences of domestic Leymus and took Bromus tectorum as outgroup. The phylogenetic trees were constructed by using the maximum parsimony method. The results showed that the tested species were classified into 3 branches and the division and the systematic relationships of taxa were basically consistent with the conclusions by morphology and anatomy.4. The evolutionary trends of characteristics, geographical distribution and the elements of geographical history and climates showed the area of the Altai region and the Qinghai-Tibet Plateau were the modern distribution center of the genus. We speculated that Leymus probably originated from Altai area region of Eurasian plant subregion in the end of Oligocene. There were two stages and three diffusion paths formed geographical distribution pattern of Leymus. The first phase was from the Altai area spreading to northern Asia and Europe, when the Qinghai Tibet-Plateau began at the early stage of uplift. The second stage was from the Tang Dynasty spreading to the surrounding area after the uplift of the Qinghai Tibet-Plateau, which included two paths. The first path started from the Qinghai Tibet-Plateau, gradual eastward spreading to North China, Spreading to the surrounding areas in local areas of North China; A branch spreaded to the Northeast China and another spreaded to East China area; The second was westerly through the Himalaya mountains spreading to Central Asian highlands; We thought that The fourth was southward, due to the barrier of Himalayan mountains of the Qinghai Tibet-Plateau, the plants of the genus only in plateau surface diffusion, no taxa along the south exit.