SUMMARYCytological studies have demonstrated the occurrence of tetraploids (2n = 28) and hexaploids (2n = 42) of theRumex acetosellacomplex in Belgium. Diploids have not been encountered. In both the tetraploid and the hexaploid races angiocarpous plants have been recorded next to gymnocarpous ones. There is a correlation between the relative frequencies of the angiocarpous individuals and of the gymnocarpous ones in the hexaploid populations and the type of soil: on the loamy soils of Central and South Belgium almost exclusively angiocarpous plants occur in the populations, whereas in the populations on the sandy soils of the coastal area and of Belgian Brabant the gymnocarpous form predominates. Tetraploids are almost exclusively restricted to the populations found on the sandy soils of northern Belgium.