Molecular dating rates vary
Differences between nuclear and plastid phylogenies can also be caused by incomplete lineage sorting or hybridization, but with 27 species spread so broadly across angiosperms, the resulting topological differences would be small if existent at all (Maddison and Knowles 2006), and topology tests would likely not be significant.On the other hand, significant topological differences due to lateral gene transfer between distantly related species cannot be differentiated from paralogy problems without a careful evaluation of the gene diversity present in diverse genomes (Christin et al. Our approach removes such sequences and is consequently conservative.
Analyses calibrated with only macrofossils lead to estimates for the age of core Poaceae ∼51–55 Ma, but the inclusion of microfossil evidence pushes this age to 74–82 Ma and leads to lower estimated evolutionary rates in grasses. The most commonly used methods differ mainly in how rate variation is modeled and, in particular, whether or not they assume autocorrelation of rates (Kishino et al. Poaceae sequences were retrieved from a published data set that includes 545 taxa (Grass Phylogeny Working Group II 2012).
We explore the effect of these in Poaceae (grasses), a diverse plant lineage with a very limited fossil record, focusing particularly on dating the early divergences in the group. 2011), angiosperm-wide dating projects have inferred a very recent origin for this same clade, between 23 and 39 Ma (Bell et al. The influence of a divergent calibration point, represented here by the most recently published phytolith fossils (Prasad et al.