To pick up the Mystical Flower (the Pax Flower), you don't have to climb the wall. When you go to the Greenhouse Area, you walk "along the wall" until you are in something like "the corner" right near the flower. When you are close enough to the flower, you will get the "interactive x" at the bottom of your screen to pick it up. It's just a matter of walking very close to the wall, and finding the "right spot".
