Buttercup

Buttercup is by far the most innocent looking plant on this list. It is also one of the most ubiquitous, and among the more deadly garden plants. Buttercup commonly grows in grassy patches with poor drainage, and may frequently be found by children who use it in games that involve touching it to the skin. The goal is to experience a momentary red mark on the skin, as the brilliant yellow flowers release a toxin induces temporary rash symptoms. Buttercup is far more dangerous, however. The plant is capable of poisoning grazing animals that eat it, causing serious gastrointestinal toxicity. Ingestion by humans may result in a painful death resulting from organ and nervous system intoxication. Beauty is clearly in the eye of the beholder, not the handler of this killer flower.