Haploidy and Angiosperm Evolution

Abstract

The frequent occur-rence of polyhaploids in cytologically well-studied groups makes untenable the dictum that polyploidy is, in an evolutionary sense, absolutely irreversible. There appears to be no theoretical reason or experimental basis for excluding polyhaploidy as an evolutionary mechanism of some importance in polyploid groups of organisms. We can no longer assume that polyploids are an evolutionary "dead end," connected only tenuously to the main evolutionary line of diploids by the rare exchange of genetic material. It even appears possible that the original diploids in certain types of polyploid complexes might become extinct, only to be produced at a later time from the remaining tetraploids. The shift back and forth between the diploid state and the tetraploid state might serve as a mechanism for adjusting the balance of fitness and flexibility for the organisms of that group through selection. Thus an awareness of the possibilities of polyhaploidy may ultimately lead to a much improved understanding of the evolutionary potentialities of polyploidy.