Oleander (lat. Nérium) - is poisonous plant. All parts of the nerium oleander are poisonous due to the contained cardiac glycosides—that is, oleandrin, nerin, digitoxigenin, and olinerin. Oleander remains toxic when dry. Cardiac glycosides that act by inhibiting the cellular membrane sodium-potassium (Na+-K+ ATPase enzyme system) pump with resulting depletion of intracellular potassium and an increase in serum potassium. This results in progressive decrease in electrical conductivity through the heart causing irregular heart activity, and eventual complete block of cardiac activity, and death.

Poisonous watercolor number 4 in my collection of poisonous watercolors