Maximum Likelihood bootstrap tree phylogeny based on amino acid sequences of CAD genes in various land plants. Numbers above branches refer to NJ bootstrap values. Brackets highlight the three classes of CAD genes. Colors indicate gene groups determined based on their expression in various Populus plant tissues. Red (group 1), green (group 2), and blue (group 3) indicate genes preferentially expressed in xylem, leaves, as well as leaves and xylem respectively. Pink (group 4) represents genes that showed no preferential expression between Populus tissues.