Datura – which Gringos call Sacred – can kill just about anything that tries to eat it. The common name is Thorn Apple, although I can't find where that comes from. It only blooms at night and has a special moth to pollinate it.
Grows all over the southwestern USA and northern Mexico. As Nature always seem to do, creatures won't graze on it because it tastes very bitter.
The reason for my interest? Simple. It plays an important part in a novel I've written that I'm currently shopping around to agents and publishers.
There are a number of other plants that cause hallucinations but without the same chance of death. The story is @ Sacred Datura: Photos of a Beautiful (But Poisonous) Plant