Polyploidy and interspecific hybridization shape adaptation, speciation and evolution

About half of all higher plant species are recognizable as evolutionarily recent polyploids, where multiple whole genomes or sets of chromosomes have come together from close ancestors. Additionally, over evolutionary time, all flowering plants have at least one polyploidy event, also known as a whole-genome duplication (WGD), in their ancestry, from before the divergence of gymnosperms and angiosperms, the ζ (zeta) event (see the legend in the paper for the many references).

Simplified phylogeny of the green plant lineage focusing on the occurrence of WGD (whole-genome duplication) events. Polyploidy events (yellow diamonds) refer to either single or multiple rounds of WGD (i.e. duplication or triplication) and are labelled where applicable (Greek letters; see references below). Complete genome sequences have clearly established that WGD has remarkably shaped the evolutionary history of angiosperms compared with the other major clades of green plants. Full details in Alix *et al*. 2017.

This Annals of Botany Special Issue on Polyploidy in Ecology and Evolution presents the evolutionary consequences of new, recent, and ancient polyploidy. Alix et al. survey experimental, genomic, ecological and theoretical studies demonstrating that polyploidization often occurs during periods of major evolutionary transitions and adaptive radiation of species. Polyploidy, the cornerstone of bursts of adaptive speciation, brings about genetic novelty. The emergence of new gene functions enables diversification, speciation, and hence plant evolution.

This paper is part of the Annals of Botany Special Issue on Polyploidy in Ecology and Evolution. It will be free access until October 2017, then available only to subscribers until August 2018 when it will be free access again.