Genesis of the floras in the arid Intermountain basins of the North Caucasus

Abstract The aim of the study was to explore history of flora formation in arid basins of the North Caucasus, and to identify the correlation between this flora and those of arid regions of neighboring areas. We applied generally accepted methods of flora study and analysis. The arid intermountain basins of the North Caucasus are an original and poorly studied formation. Surrounded by forest and alpine vegetation, they have preserved in their composition a xerothermic flora that differs from the flora of the steppe of the Ciscaucasus and takes in the features of the flora of the Southwest Asia and the Mediterranean region. The first large array of arid vegetation is located in the upper reaches of the Kuban River in the Jurassic depression, which runs between the Main Caucasian and Side ridges. Further to the East, arid basins are founding in the basins of all major tributaries of the Terek River. After the Argun and Sharoargun rivers in the Republic of Dagestan, the xerothermic vegetation of the arid basins are replaced by a belt of upland xerophytes of mountain dry and desert steppes, which stretches to the south and connects with the arid regions of the Eastern Transcaucasia. Our studies show a genetic relationship between the flora of the arid basins of the North Caucasus and the areas of xerothermic vegetation on the one hand in Azerbaijan and Iran, on the other-in the Mediterranean, from where its formation began in the territory under consideration. The xerothermic period of the late Miocene is the driest in the history of the Caucasian flora and contributed to the deep penetration of the Southwestasian arid flora into the territory of the North Caucasus after the connection of the Caucasian Isthmus with the southern mainland.