The poisonous passion flower

The passion flower is a show-stopper for more than one reason. Yes, it immediately catches the eye and I couldn’t just walk past it when I spotted it growing wild in Pembroke. But, hiding within its leaves is a rather deadly secret – they contain cyanide, a chemical that’s poisonous to much of the animal world. 


To be exact, the leaves contain cyanide in an inactive form – bound to sugars as chemicals known as cyanogenic glycosides. When tied up like this, the cyanide is harmless. But the cyanide doesn’t always remain inactive – right nearby, the leaves also contain other specialized chemicals that break these sugars down. Known as enzymes, they fit together with the cyanogenic glycosides like a lock and key. When they combine, the sugars are broken down and the poisonous cyanide is released.  


Normally the sugars and enzymes are stored in separate compartments within the leaves’ cells. But when a hungry herbivore starts to munch on the leaves,  these boundaries are broken down and the sugars and enzymes mingle together in the unlucky animal’s mouth. The poison works on both insects and animals, and this is a brilliant evolutionary mechanism that stops the plant being eaten. In fact its such a successful strategy, that it’s repeated over and over again in the plant world. 


Typically, the animal sickens rather than dies, and a casual bystander has nothing to worry about. But this isn’t a plant you’d want to make a diet staple if stranded in the wild.


(Species name: Passiflora caerulea, Maltese Name: Fjura tal-passjoni)