Cytogenetical relationships between Rumex tuberosus, R. thyrsiflorus and R. acetosa and occurrence of polyploidy among their hybrids.

Reciprocal crosses were performed between Rumex tuberosus and two other taxa belonging to the Acetosa group: R. acetosa and R. thyrsiflorus. All three taxa are dioecious with the same chromosome numbers, ♀ XX + 12A, ♂ XYY+12A, but they differ from one another in the morphology of some autosomes. R. tuberosus and R. thyrsiflorus are similar in external morphology, while R. acetosa differs greatly from the other two taxa in external morphology as well as ecological characteristics.The F 1 and F 2 hybrids were fully vigorous and viable but their fertility was greatly reduced. Meiotic irregularities were observed in hybrids derived from all crosses. The most remarkable meiotic irregularity was diad formation after first meiotic division. The unreduced gametes derived from diads were responsible for the high frequency of polyploidy observed among the F 2 hybrids. In the cross R. tuberosus × R. acetosa the whole F 2 generation was tetraploid.It is concluded from the analysis performed that R. tuberosus, R. acetosa and R. thyrsiflorus are separate species, closely related to one another but already isolated by genetic and ecological barriers.