The lignin biosynthesis pathway. Coloured dots represent the presence of a given enzyme in a specific taxonomic group. The abbreviations used for the enzyme are: phenylalanine ammonia-lyase (PAL); cinnamate 4-hydroxylase (C4H); 4-coumarate:CoA ligase (4CL); cinnamoyl-CoA reductase (CCR); cinnamyl alcohol dehydrogenase (CAD); peroxidase (PER); and laccase (LAC). Question marks (?) indicate that the enzyme responsible for a specific function or its substrate is unknown, or that the presence of a particular compound in a given taxonomic group is hypothesized but has not been demonstrated.