The xylem transcriptome is relatively more conserved in vascular and non-vascular plants. Xylem gene indices and total gene indices of pine, spruce and poplar were blasted (blastn and blastx) against the gene models of Populus, Arabidopsis, rice, Selaginella and moss. Percentage of hits is presented on the Y-axis at E-value cut-offs of 1e-50 and 1e-5. Statistical tests for the different number of hits observed with xylem and total gene indices were performed assuming a binomial distribution. All comparisons showed statistical significances (P < 0.001) (data not show for the simplicity of the figure) except for two comparisons between conifer species and poplar (blastn at 1e-50).