Phylogenetic reconstruction of the genes used in this study. Angiosperm gene family keyword search was performed into Phytozome (http://www.phytozome.net/search.php) and A. thaliana and P. trichocarpa genes were retrieved and aligned to a consensus Salix sequence generated from our study. Midpoint rooted, bootstrapped trees were generated using maximum likelihood analysis in PhylML 3.0 with HKY85+G substitution model (estimated gamma shape parameter and four substitution rate categories) and NNI branch swapping. Bootstrapping included 1000 replicates with the same model and branch swapping. Asterisks indicate nodes with 80% or higher bootstrap support (Ptr: P. trichocarpa, AT: A. thaliana). The 4CL2 gene tree is given as an example (NCBI accession: AF041050, Populus tremuloides clone Pt4CL2 4-coumarate: CoA ligase mRNA, complete cds).