Hybridization, polyploidy and speciation inSpartina(Poaceae)

Abstract

SummaryHybridization and polyploidy are well illustrated in the genusSpartina. This paper examines how recent molecular approaches have helped our understanding of the past and recent reticulate history of species, with special focus on allopolyploid speciation.Spartinaspecies are tetraploid, hexaploid or dodecaploid perennials, most of them being native to the New World. The molecular phylogeny indicates an ancient split between the tetraploid and the hexaploid species, withS.argentinensisas sister to the hexaploid lineage. Recent hybridization and polyploidization events involved hexaploid species, resulting from introductions of the east‐AmericanS. alterniflora. In California, ongoing hybridizations with its sister speciesS. foliosaresult in introgressant hybrid swarms. In Europe, hybridization withS. maritimaresulted inS. × neyrautii(France) andS. × townsendii(England), with.S. alternifloraas the maternal parent. The allopolyploidS. anglicaresulted from chromosome doubling ofS. × townsendii.This young allopolyploid contains divergent homoeologous subgenomes that have not undergone significant changes since their reunion. Hybridization, rather than genome duplication, appears to have shaped the allopolyploid genome at both the structural and epigenetic levels.