Chemical evolution within the Asteridae

Abstract

Chemical evolutionary pathways operating in the subclass Asteridae have been critically assessed. The different groups of plants are found to experiment with the various plant products such as alkaloids, cardiac glycosides, tannins, volatile oils, quinones and iridoids. Compounds which help plants to combat pathogens, discourage herbivores and act as allelochemics are found to provide a selective advantage to those individuals that possess them. Compounds providing little or no selective advantage are discarded. Trends in the chemical evolution of Asteridae are (i) reduction/elimination of alkaloids, flavonols and proanthocyanidins/tannins, (ii) introduction and further methoxylation of 6-deoxy and 6-oxyflavones, (iii) introduction of iridoids especially aucubins, (iv) development of volatile oils rich in sesquiterpenes, and (v) increased reliability on quinones as antimicrobials and allilochemics. The advanced groups of Asteridae possess a specific assortment of antimicrobials, bitter substances and allelochemics. The classification within the Asteridae is examined in the light of these trends.