Most plants contain some level of toxins (like alkaloids) for defense. After all, they’re plants. They can’t go anywhere. Through millennia of trial and error, both animals and human beings have figured out which plants are safe, which are lethal, and which are somewhere in between. For example, did you know that many grain-bearing plants contain a toxin known as lectins? And that the African staple, cassava, must be thoroughly boiled and soaked to separate it from its poisonous compound, cyanide? Even the humble lima bean has been bred to contain less cyanide. Cherries, potatoes, peaches and apple seeds are all toxic - eat enough of the latter, in fact, and it will prove fatal. Fortunately, artificial selection and cooking methods have all but eliminated the threat of toxins in everyday foods. But you may be surprised to find out the incredibly lethal plants often hanging around the neighborhood park - or gracing your tabletop in the form of a centerpiece.
more:
http://webecoist.com/2008/09/16/16-most-unassuming-yet-lethal-killer-plants/