Amy Stewart has written a fascinating book called Wicked Plants. The subtitle is "The weed that killed Lincoln's mother and other botanical atrocities."  In her introduction,  Stewart states:

"I confess that I am enchanted by the plant kingdom's criminal element... there is something beguiling about sharing their dark little secrets, and these secrets don't just lurk in a remote jungle. They're in our own backyards."

Some of the toxic flowering plants that Amy Stewart discusses are azaleas, Rhododendrons, daphne, opium poppies, larkspur, delphiniums, lily of the valley, and bleeding heart. Others poisonous flowers to be weary of are sweet peas, tulips, hyacinths, chrysanthemums, and aconites.

Victim of Milk...

I recall a famous murder case of a man who ate a salad where shredded aconite leaves had been added to the lettuce. Nancy Hanks Lincoln died of milk sickness at 34 when her son Abe was only 9.

Milkweed sickness is caused by cows eating white snakeroot, which has flowers that are similar to Queen Anne's lace.

The book Wicked Plants is published by Algonqium Books of Chapel Hill, 2009.