The Monkshood. Also called Mousebane because its scent supposedly killed mice... Whether that's true or not, it can sure kill humans.
Despite its lovely demeanor, the Autumn Crocus can cause symptoms similar to those of cholera.
The Castor Bean - also known as the Castor Plant - can make one helluva laxative.
A few killer plants illustrated for "Idiots in the Poison Garden," an unofficial board game based on the infamous Alnwick Poison Garden.
"You and three other friends are trapped in an enclosure of lovely plants. The problem is that you are all idiots and these plants kill! How long can YOU survive... and how will you die?"