In her book Wicked Plants, Amy Stewart tells all about toxic houseplants. She notes that houseplants must survive in a year-round indoor climate of 50-70 degrees Fahrenheit so most are tropical plants originally from South America or Africa.
The Peace Lily is originally from South America and has white flowers which look like a simpler version of the calla lily. However, Stewart tell us that in 2005, more calls were made to poison control centers about poisoning with peace lilies than were made about any other plant. So it has the dubious honor of being the most anxiety provoking house plant.
Peace lilies contain calcium-oxalate crystals that can cause irritation to the skin, mouth burning, swallowing difficulties, and nausea. (Another house plant that keeps poison control centers busy is the common philodendron which also contains calcium oxalate; over 1600 calls to poison control centers about philodendrons were made in 2006 alone).
It seems ironic that a plant with the name Peace Lily would be called a wicked plant, or that such a common houseplant as philodendron is considered poisonous.
The book Wicked Plants is published by Algonqium Books of Chapel Hill, 2009.