Right now, it has 28 member states: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Italy, Ireland, Latvia, Lithuania, Luxembourg, Malta, The Netherlands, Poland, Portugal, Romania, Spain, Slovakia, Slovenia, Sweden, and The United Kingdom.
The Northern European plain and lowlands of West Siberian Plains have a lot of differences in terms of their characteristics. The only similarity between the two would be the vast complex land that both of these lands have.