Frequent gain and loss of pyrrolizidine alkaloids in the evolution of Senecio section Jacobaea (Asteraceae)

All 24 analyzed species of Senecio sect. Jacobaea synthesize pyrrolizidine alkaloids (PAs) that are biogenetically derived from senecionine. Optimization of the 26 PAs that were identified in sect. Jacobaea on a phylogenetic tree of this species group indicates that 'on/off' changes in the production of individual PAs in the evolutionary history of sect. Jacobaea have been remarkably frequent.