关键词: 甘肃, 藜科, 区系特征, 区系分区, 起源

Abstract: Based on the collection and identification of the specimens of the Chenopodiaceae, there are 67 species that belong to 8 tribe and 21 genera in this region. The abundant distributions areas are Hexi Zoulang and South Gansu(east edge of Qinghai-Tibet Plateau).The results of floristic analysis indicate that on the level of genera, except for the Cosmopolitan elements and the endemic elements of China, all the distribution types are temperate elements which has a percentage of 71% in total genera, especially dominated with the type of Mediterranea, W.Asia to C. Asia. It shows that the Temperate Zone is the decisive factor of the floristic characteristics. According to the analysis of relic species, the floristic origin is ancient. Comparing with the species between Gansu and neighboring provinces, the flora is widely related to Ningxia, Neimenggu and Qinhai. The analysis of floristic formation shows that the place of origin of the Chenopodiaceae is Eurasia. During the Cretaceous Period, the time of origin of the Chenopodiaceae, most places of the continent of Eurasia were occupied by the ancient precursor to the Tethys Sea, therefore, primitive Chenopodiaceae likely originated on the beaches of the Tethys Sea which had an arid climate. With the development of the orogeny of Himalayas Mountains beginning from lateTertiary Period and the west Central Asia became continent, the environment became arid and some place desertification, forming the main characteristics and distribution patterns of the flora now. Finally, based on the study of the flora and the principles of the floristic division, the flora of the Chenopodiaceae in Gansu was divided into 5 floristic subregions: subregion of Qilianshan, subregion of Zhongbu, subregion of Gannan, subregion of Longnan. The floristic features of each subregions and suggestions were discussed in detail，especially subregion of Zoulang and subregion of Gannan, which are the main agricultural region and grassland stockbreeding area. And it has theoretical and practical significance to the reconstruction of pasture, vegetation restoration and the control of desertification.

Key words: Gansu, chenopodiaceae, floristic characteristic, floristic division, origin