XVI International Botanical Congess

By regular karyological study (over 20 years) of population of Crepis pannonica in south of the area (Armenia, Chosrov) a striking spontaneous polymorphism is discovered. Population is presented with di-(2n=2x=8) and triploid (2n= 3x=12) cytoraces. But seed progeny is characterized by polymorphism according to the autosome number (2n=8-16) and 1-4,6 B-chromosomes of standard and derivative types. 40 variants of number polymorphisms are fixed. A great range of structural chromosome mutation is discovered, 9 structural hetero- and 1 homozygotes are described. High level of structural rearrangement of karyotype in a con- crete population is a precondition of B-chromosomes creation. B-chromosomes are viewed as centric fragments appearing during structural changes. It is obvious, that this population characterizing by this karyotypical liability is a center of variety-formation and speciation.