The most deadly tree in the world, the Manchineel, can only be found in one place in the United States: South Florida, mainly the Everglades. We should all be thankful for this because the Manchineel is so dangerous that you can't even touch any part of it. And eating it is an especially bad idea.
The meme that "natural is safe" can get you into trouble in many ways. It's one that's appropriate at this time of year, when gardens and flowers are on our minds, since some plants are naturally deadly. Here are a few commonly found in our gardens and often available from nurseries, as well.