Abstract
Karyotype measurements of two dioecious species of Rumex, namely, R. hastatulus (subgenus acetosa) and R. acetosella (subgenus acetosella) and their F1 hybrids; F1+=(R. hastatulus 2n=8) _??_×(R. acetosella 2n=42) _??_ and (R. hastatulus 4n=16) _??_×(R. acetosella 2n=42) _??_ were recorded. The acetosella chromosomes are much smaller than the hastatulus chromosomes and can easily be identified in the hybrids. A significant decrease in the size of the R. acetosella chromosomes (particularly the sex chromosome) and a compensating increase in the size of the R. hastatulus chromosomes were found in the F1 hybrid karyotypes when these were compared with the chromosome sizes in the parental karyotypes. Apparently the genetic and physiological balance resulted in shortening of the shorter chromosomes and lengthening of the longer chromosomes.
