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Defensive Compounds
Like most Brassicaceae, species in the genus Erysimum produce glucosinolates as defensive compounds. However, unlike almost all other genera in the Brassicacaea, Erysimum also accumulates cardiac glycosides, another class of phytochemicals with an ecological importance in insect defence. Cardiac glycosides specifically function to prevent insect herbivory and/or oviposition by blocking ion channel function in muscle cells. These chemicals are toxic enough to deter generalist, and even some specialist insect herbivores. Cardiac glycoside production is widespread in the Erysimum genus, with at least 37 species in the genus containing these compounds. Molecular phylogenetic analysis indicates that Erysimum diversification from other Brassicaceae species that do not produce cardiac glycosides began in the Pliocene (2.33–5.2 million years ago), suggesting relatively recent evolution of cardiac glycosides as a defensive trait in this genus.