Fifty-percent majority-rule Bayesian tree inferred form the intron sequences of nuclear Acc1 gene of Leymus and its affinitive species, under GTR + G model. Numbers with bold above nodes are Bayesian posterior probability values ≥ 90% numbers below nodes are bootstrap values ≥50%. The numbers after species names refer to the distinct homoeologous of Acc1 gene. The table provides the estimated divergence dates for nodes labeled 1-13. The letter a and b represent two different accessions of Agropyron cristatum. This figure shows the upper quartile, for the full image please see Additional file 5.