XVI International Botanical Congess

Island isolation usually leads to reducing in species diversity whereas richness of High Arctic Wrangel Island (WI) (N 71?) in vascular plant species is extremely high: about 390 species and subspecies for 7 600 km2. This can not be explained by only landscape and bedrock diversity or by uninterrupted by transgressions and glaciations late Cenozoic history of the island. Northern part of the Bering Land Bridge including WI, which exposed several times during the late Cenozoic, was an area of intensive migration of plants. WI was never occupied by oligotrophic subarctic vegetation dominating in neighboring Chukotka, although modern climate of interior parts of the island and warm periods of Quaternary time are suitable for subarctic vegetation. Only limited number of subarctic species survives in the island. Intensive speciation and hybridization of arctic and arctic-alpine plants was and is facilitated by lack of competitive subarctic species, which makes new kind of habitats available for arctic and arctic-alpine taxa.