Salt tolerance is evolutionarily labile in a diverse set of angiosperm families

Background: Salt tolerance in plants is rare, yet they it is found across a diverse set of taxonomic groups. This suggests that, although salt tolerance involves a complex set of traits, it has evolved many times independently in different angiosperm lineages. However, the pattern of evolution of salt tolerance can vary dramatically between families. A recent phylogenetic study of the Chenopodiaceae (goosefoot family) concluded that salt tolerance has a conserved evolutionary pattern, being gained early in the evolution of the lineage then retained by most species in the family. Conversely, a phylogenetic study of the Poaceae (grass family) suggested over 70 independent origins of salt tolerance, most giving rise to only one or a few salt tolerant species. Here, we use a phylogenetic approach to explore the macroevolutionary patterns of salt tolerance in a sample of angiosperm families, in order to ask whether either of these two patterns - deep and conserved or shallow and labile - rep...