Biosystematic relationships and the formation of polyploids

Since the discovery of polyploidy (the presence of more than two chromosome sets in a nucleus) a century ago, scientists have investigated and speculated about the factors that could promote polyploid formation. One of the oldest and most enduring ideas is that hybridization promotes whole‐genome doubling. First suggested by Ø. Winge, this concept was developed and refined by the major plant evolutionary biologists of the last century, and especially in the biosystematic thinking of J. Clausen, D. D. Keck and W. M. Hiesey. In the past few years, this issue has been revisited by various authors, using molecular systematic methods to study patterns of parental divergence in relation to the formation of polyploids. Progress in molecular genetics and genome evolution also allows re‐appraisal of the mechanistic arguments put forward by earlier researchers. Here we survey and critically appraise developments in this field over the past century, and conclude that in the light of recent progress there is not currently persuasive evidence that hybridization between divergent parents serves as a driver for polyploidization.