If you cut down a cactus in Arizona, you are penalized for up to 25 years in jail. It is similar to cutting down a protected tree species.
If you cut one down without permission, you could go to jail for up to 25 years. Clearly, this is not a mistake you want to make. One important thing to note about this law is the wording. The maximum time you could get in jail is 25 years. This is not a mandatory term that is handed out to everyone. If you make an honest mistake, you're far more likely to get a much lighter sentence. If the judge feels like throwing the book at you, though, you could, technically, be locked up for quite some time.
The reason this law stands is that the saguaro cactus, prevalent in Arizona, takes an incredibly long time to grow. These plants have a lifespan that is estimated to be from 150 years to 200 years if they aren't cut down and if they have the right conditions. As such, when they are ten years old, they might still be tiny, perhaps under two inches tall.
Because of this, the state is harsh on those who cut them down. If they were harvested quickly, it could be generations before they'd be able to grow back. Any damage that is done by a human will last for the rest of that person's life. While trees can be replanted and some will grow up again relatively quickly, the same is not true for the saguaro cactus.