You wonder what evil magic has been placed on you. You consider your hand where the thorn made you bleed and notice the skin around it is discolored. But Elthissa said it wasn't poisoned? The discoloration seems to be slowly spreading and soon your entire hand has lost it's fleshy color. At first your skin turns a sickly yellowish color, but this too slowly shifts into a shade of green.
Better find your father, the king, and quick! You don't know what is going on, but hopefully his wizard can undo whatever magic spell is upon you. As you make your way through the gardens you notice a strange tingling sensation in your arm that gives way to a pleasant warm feeling. The warm feeling begins to fade again, then starts again. Hmmm...that is odd. You stop and wonder what made the feeling start and stop like that? Looking at your arm, the green color has now spread all the way up your arm under your sleeve. Looking back the way you came you notice you passed through an area heavily shaded by some trees, but are now back in the sun.
Your skin is turning green...like a plant? You retrace your steps and sure enough the warmth in your arm begins to fade in the shade. Stepping back in the sun the warmth returns yet again. You may not be familiar with photosynthesis, but you know plants like the sun. It seems you are turning into a plant.