More than 70 bitter glycosides with cardiac activity, with five different aglyconees digitoxigenin, gitoxigenin, digoxigenin, diginatigenin and gitaloxigenin in the leaves act as a protection against herbivores. Yield and concentration of these cardiac glycosides are enhanced by greenhouse cultivation through enhanced temperature and enhanced carbon dioxide concentration.
The leaves remain somewhat turgid even under very low leaf water potential, due to osmotic adaptation by synthesis of non-ionic substances in the leaves. The drought induced diminishing of photosynthesis is reversible after a few hours following watering of the plants.