Figure 1

Pruned phylogenetic tree of seed plants. Blue circles represent duplication events previously proposed (for example, [10]). The black circle denotes the hexaploidy event shared by most, if not all, eudicots. The red line represents the Cretaceous and Tertiary boundary (KT). Although the dating of several of the whole genome duplications (WGDs) is still controversial, many of the more recent WGDs might be clustered in time close to the KT extinction event (grey area) [9]. The two newly discovered ancient WGDs discussed in Jiao et al. [1] are shown as red circles.