Prunus mongolica(Rosaceae subfamily Prunoideae) is a perennial desert xeric shrub native to the Mongolian Plateau.It is an ancient relict plant that mainly grows in extreme environments,such as on low mountains and hills,on stony slopes,and in dry beds in the desert and desert steppe regions.P.mongolica has distinct xeromorphic adaptations,such as hard shoot spines at the ends of the branchlets.P.mongolica is an important woody oil crop with a high oil content in the seed kernel,and oil extracted from the seed kernel can be eaten.In addition,because of its long flowering period(a single flower can last eight days,and a community flowers for 50 days),flamboyant flowers,and extreme tolerance to harsh conditions,P.mongolica can be used as garden plant in the northwest of China.Zhao Yizhi proposed that P.mongolica is an Alax desert species that is mainly distributed in the Alax desert regions of the Mongolian Plateau,although scattered populations can be found in the southwest regions of the eastern Gobi Desert.Because the shrubs are limited by environmental conditions,P.mongolica cannot form large desert populations;it is only found scattered in the mountains and gullies.Such habitat fragmentation may influence the genetic diversity and evolutionary potential of the species. In recent years,a number of researchers have studied the geographic distribution,physiological and ecological characteristics,tissue culture,flower morphology,and insect pollinators of P.mongolica.However,no studies on the genetic diversity of its populations have yet been reported.The fragmented distribution could cause genetic differences among individuals or populations.Our field observations of P.mongolica in different areas of western Inner Mongolia indicated that P.mongolica had abundant morphological diversity,such as differences in shoot spine number,leaf size,and plant height,that suggested genetic diversity.We analyzed the genetic variation,genetic diversity,and genetic structure of different natural populations of P.mongolica,in order to elucidate the adaptive mechanisms and evolutionary potential of P.mongolica in arid and nutrient-poor environments and to provide data for its effective protection. In this study,we analyzed the genetic diversity of six P.mongolica populations in Inner Mongolia using inter-simple sequence repeat(ISSR) markers.The results were as follows:(1) Twelve ISSR primers amplified 200 DNA fragments,of which 199(99.5%) showed polymorphisms among the populations.The percentage of polymorphic bands at the population level ranged from 43% to 67%,with an average of 55.3%.Nei′s index and Shannon′s information index were 0.3241 and 0.4875,respectively,at the species level,and 0.3105 and 0.4722,respectively,at the population level.Gene flow(Nm) among the populations was 0.8266,based on the genetic differentiation coefficient.(2) UPGMA analysis shows that the Wuhai Qianligou and Dongshengmiao Narenwula populations were the most genetically similar of all the populations.The Baotou Salaqi population should be given priority for conservation,because it had the highest genetic diversity among all the six populations investigated.(3) We compared the leaf length/width ratio,and the results generally agreed with the UPGMA analysis.(4) A comparison of the morphological characteristics of the six populations showed that plant height and crown width were affected by the degree of aridity of the habitats.In particular,plant height(0.45 m and 0.26 m,respectively) and crown width(0.74 m and 0.43 m,respectively) of the Wuhai Qianligou and Dongshengmiao Narenwula populations were distinctly less than in the other four populations.