Whole genome duplication is often associated with gains in plant developmental complexity. Does this include secondary metabolites?
Carnivorous plants need to manufacture a variety of specialised chemicals to lure, trap and digest prey.
Plants can encourage rhizobacteria to help fight of rot-knot nematodes.
Flowering plants have had an intimate relationship with insects for millions of years. Indeed, this is often cited as an example of co-evolution , particularly with regards to the flowers and their pollination by the insects. However, this has also given parasites millions of years to adapt too.