Like Shurtle said, if it is a map that was made in map maker, the plants are most likely just bigger than your character even if you're full size. I have some maps that are like that, where everything is taller than it should be, making all of my characters look tiny compared to them. It shouldn't be something to worry about. If it is like that in public maps, it could be a glitch, but I never heard of that happening before.