SUMMARYDetailed karyomorphological analysis of a species (Viscum capitellatum Sm.) in the family Viscaceae is reported for the first time. The exceptionally large chromosomes in V. capitellatum probably represent the largest chromosomes in dicot angiosperms. The chromosome number of the species has been found to be n = 10 and 2n = 20. One pair of the chromosomes is heterochromatic. It is suggested that unequal crossing over of a segment between the homologous chromosomes has resulted in one duplicate chromosome and the other deficient.