Polyploidy, hybridization and reticulate evolution: lessons from the Brassicaceae

The family Brassicaceae is well known for its large variation in chromosome numbers, common occurrence of polyploids and many reports of interspecific gene flow. The present review summarizes studies from the past decades on polyploidization and hybridization events, recognizing them as important evolutionary forces in the family. Attention is drawn to the issue of the reconstruction of reticulated pattern of evolution resulting from allopolyploid and homoploid hybrid speciation. The research of various authors on several Brassicaceae genera is presented and discussed in the context of our current understanding of polyploid and hybrid evolution. Model species, Arabidopsis thaliana and Brassica taxa, are referred to only marginally, major focus is on a comprehensive survey of studies on about a dozen best explored non-model genera (e.g. Cardamine, Draba, Rorippa, Thlaspi). The increasing amount of genetic and genomic resources available for Brassicaceae model species provides excellent opportunities for comparative genetic and genomic studies. Future research directions and challenges are thus outlined, in order to obtain more detailed insights into the evolution of polyploid and hybrid genomes.