Polyploidy in plants has been studied extensively. In many groups, two or more cytotypes represent separate biological entities with distinct distributions, histories and ecology.
Mandák et al. analysed ploidy level variation in populations of Alnus glutinosa over the whole Europe. In addition to diploid populations they for the first time report the occurrence of tetraploid populations of A. glutinosa. The distribution of tetraploids is far from random, forming two, geographically very well delimited populations. The first one is situated in the Iberian Peninsula extending to North Africa. The second one occupies the area of the Dinaric Alps extending to south-western Greece.