Chelidonium majus, also known as wartwood or swallow wort, is a perennial in the papaveraceae (poppy) family. Found in damp ground in rubble, banks, near hedgerows and walls, wartwood is recognizable by its upright form (growing to about 0.5m) and little yellow flowers that bloom May-August.
While the whole plant is poisonous, its toxicity is greatly reduced through drying. It has a long history in herbal remedy - often being used as a sedative. The bright-orange sap is both stains and severely irritates the skin.