中文摘要：

运用植物区系地理学的研究方法,根据古植物学资料及与现代植物区系的对比分析,对陕北黄土高原植物区系的演变及新生代植物区系进行了研究,对深入了解陕北黄土高原植物区系、植被的起源和发展具有重要意义,同时为指导本区目前实施的退耕还林还草、植被恢复等生态环境建设方面可以提供参考。文中论述了自白垩纪以来各时期陕北黄土高原植物区系的演变发展过程,对陕北黄土高原植物区系的演变和现代与新生代孢粉植物群进行了比较分析,认为本区植物区系主要来源于4个方面：一是起源于本地及邻近地区晚白垩纪-早第三纪植物群,一些草本植物和湿生植物主要发生于晚第三纪,耐寒和耐旱的种类主要发生于第四纪;二是来源于地中海区-中亚和欧亚草原;三是来源于东北亚、西伯利亚温-寒地区;四是来源于我国西南、西北、华北及秦岭、华中地区。

英文摘要：

Flora study is basic to the understanding of the intrinsic attributes of regional vegetation and its zoning,management,and utilization.Therefore,studies on the flora geography of the Loess Plateau of Northern Shaanxi Province will be important not only for the Loess Plateau Flora zoning,but also for the flora studies of Western China,local planning of its agriculture,forestry and animal husbandry industries.It will also have reference value for the utility and protection of local plant resources.In short,the study of the flora geography will have ecological,economic and social importance in the ecological improvement and natural resources protection.Comparative analysis of material between paleobotany and present-day flora of the Loess Plateau of Northern Shaanxi Province（LPNS） shows the evolution and sources of the LPNS＇s flora.The evolutions of flora over stages since the Cretaceous period are discussed.From the flora evolution and the spore and pollen comparison between the modern and the Cenozoic period,it is believed that the flora of the LPNS can be dated back to four major sources： ①the local and neighboring flora in the late Cretaeous period and Paleogene,with some herbaceous plants and hygrophytes originating in the Neogene and the hardy and drought enduring plants in the Quaternary period;②the Mediterranean,Central Asia and the Eurasian Steppe;③the Northeast Asia,the temperate and cold area of Siberia;④the Southwest China,Northwest China,North China,and the Qinling Mts.and Central China.