Performance of maximum parsimony (MP) and maximum likelihood (ML) phylogenetic methods for varying levels of heterotachy (τ) and increasing rate variation among species in the Felsenstein zone. For three combinations of p and q (a, b, c), the performance of MP and ML in the Felsenstein zone (i.e. p > q)  was evaluated under varying levels of heterotachy. The accuracy was calculated as in ref.  with BL50, i.e. the estimated internal branch length that allows recovering the true tree 50% of the time in 100 simulations using PAUP* .