Here are some pictures I took of Chelidonium majus, Greater Celandine.
What makes it so special? Well, C. majus is a member of the buttercup family (Ranunculaceae) and bleeds bright yellow latex when you break it.
The plants contains many isoquinoline alkaloids, the main one being coptisine, among many others. It is used in herbalism in many ways, including use to treat warts, toothache relief and as a foot refresher.